4

BREWHOUSE OPERATIONS

The precise method of brewing Gose was of great secrecy in the eighteenth and nineteenth centuries. The beer’s popularity (and the premium price that it commanded) made it an attractive proposition for any brewery. Naturally, those already in the business of making it weren’t too keen on their rivals getting in on the act. The tricky part was getting the addition of lactic acid bacteria right. Sometimes during the boil, the precise moment was of great importance, a powder was added to the wort (according to a source of 1872).

—As reported by Ron Pattinson, “Leipzig Pub Guide: Leipziger Gose,” European Beer Guide (website).

A thousand years ago, when the first Gose-style beers were first being brewed, the world was a very different place in many ways. Brewers were often also maltsters, and sometimes even farmers. Milling the malt would probably have taken place at a community mill shared with the local baker; lucky brewers may have had their own mill driven by a donkey walking endlessly in circles.

MILLING

Today, almost all brewers get their grain already malted, some get it pre-milled, and some even use malt extract. For most brewers, all that is required of their malt is that it is properly cracked and captured in a grist case. To do this there are many good mill options, from benchtop homebrew mills, to the Roskamp two-row mill, to the Kunzel six-roll for the larger breweries. The key difference between Gose-style beers and other beers is that you are milling approximately 50 percent wheat and 50 percent barley. The kernel size of these two grains may be different enough that the roller gap of the mill will need to be adjusted. The other main difference between the two grains is that wheat is a huskless grain and can be more finely milled.

However you mill your grain, the goal is to crack open the kernel and expose the inner starch. Most of the malt husks should be relatively intact, split into halves or quarters, and not pulverized. The chalky inner starch should be exposed and broken. In a proper grind from a two- or even four-roll mill, you can expect to see a few uncracked kernels, but not many; aim for less than one percent.

Figure 4.1. Properly milled barley malt. Note that there are not very many whole grain kernels and the majority of the husks are broken open, but not pulverized.

Too coarse of a grind will lead to insufficient amino acids and low sugar yields in your wort. Too fine of a grind will lead to more phenols and husky flavors (at least for the barley portion of the grist) and longer lauter times.

If you have the ability to steam condition your malt, or if you are able to wet mill, both these hydrating processes will help to keep the starch-encapsulating layers of the wheat and the husks of the barley malt more intact. This in turn will help to keep the mash bed looser during lautering and make for an easier runoff to the kettle.

Detour 1: Sour Mashing

It is at this point that that we hit our first fork in the road. What method of souring are you planning to use? Will it be a sour mash, a kettle sour, or will you sour post-brewhouse operations? If you chose number one, come back to this section after you have read the first section on “Souring the Beer”. If you have chosen either of the latter two options, please continue reading.

MASH-IN

Mashing in a Gose needs to be done with care. Although this is a relatively low-gravity beer, it is at least 40 percent wheat and can be as much as 60 percent wheat, or even 100 percent if you are making an all-wheat Gose from the Middle Ages. This is pertinent, because the viscosity of the wort created from wheat malt is higher than that from barley malt, and because wheat is a naked grain and has no husk to help build a filter bed in the lauter tun. With a grist bill that is 40 percent wheat malt or greater, you will have 40 percent less husk material to aid runoff. Because of the lack of husks, a Gose or other wheat beer mash will not form the same kind of constructed mash bed that a 100 percent barley malt mash will. This, coupled with the higher protein content of wheat, can make for a very dense, sticky mash and you can expect to have some lautering difficulties. To alleviate some of these issues, a brewer may choose to conduct a protein rest around 122°F (50°C). This rest will allow for some for the high molecular weight proteins to be broken down and thus decrease wort viscosity. This can easily be done using a step-infusion mash regime. Brewers who are planning on using more than 50 percent wheat malt in their grain bill, especially when used in conjunction with under-modified malts, may opt to use a non-traditional decoction mash regime. Decoction mashing is usually accomplished by doughing-in at around 122°F (50°C) for a protein rest, waiting for 20–30 minutes, then removing one third of the mash, sending it to another vessel, and bringing it to a boil. The boiled portion is then returned to the main mash and blended to attain a temperature of 148–156°F (64.5–69°C). This process will give you maximum protein degradation, and will break down starch as well. Decoction mashing is complicated, time consuming, difficult, and involves a lot of mixing that can cause further problems with lautering. You will have to decide if your brewing equipment is suited to the task, and if the benefits of the extra steps are justifiable. If not done properly, decoction mashing can lead to a scorched mash, darker beer color, denatured enzymes, and husky or burnt flavors.

Another option for reducing lautering difficulties is to use rice hulls (or spelt hulls) in your mash. Rice hulls are flavorless and will not impact the color of your beer. They will help you establish a suitable mash bed matrix that will allow for acceptable wort flow, runoff times, and mash tun efficiencies. I suggest using between 0.2 and 1 oz. (6–28 g) of hull material per pound of malt in the mash, depending on your grain bill and lauter system. Mix the rice hulls in with the rest of your grain so that they are evenly dispersed throughout the mash. For those brewers in Europe who have a hard time finding rice hulls, spelt hulls are more accessible and work well too. It is suggested that you soak the spelt hulls for 4–12 hours before using them.

In my opinion, it is better to use 50 percent or less wheat malt in your grain bill with highly modified barley malt, employ a single temperature mash, and throw in some rice hulls. With today’s well-modified malts, using a complex mash regime is avoidable and probably unnecessary. All that is required for a Gose mash is an infusion rest at 148–152°F (64.5–66.7°C)

Keep in mind that the ABV on these beers is between 3 and 5.5 percent. Original gravities should be low as well—between 8 and 13°P (1.032–1.052). This equates to about 1.5–2.2 lb. per gallon (~0.18–0.26 kg/L) of wort post boil, depending on your desired gravity and equipment capabilities. Finishing gravities in a Gose should be low at 1.5–3°P (1.006–1.012). A saccharification rest at 148–152°F (64.5–66.7°C) is recommended to achieve this.

When doughing-in, or mixing your grain with hot liquor, the key word is gentle. Do not over stir your mash, as excessive mixing will beat out the entrained air attached to your grain particles. This air helps buoy up your mash bed, and that will be a good thing during lautering. If you remove the air by overmixing, it will lead to a compacted mash bed, and too long (and in some cases very long) lautering times.

It’s important to remember throughout the process to measure the pH in your brewhouse. A proper pH is especially important in the mash tun. Alpha- and beta-amylase enzymes work best under specific pH ranges. If your pH is too high or too low, your enzyme activity will be hampered or even possibly eliminated.

Water and mineral additions are covered in the “Water” section in chapter 3.

Before proceeding with recirculation, an iodine test should be done to confirm full starch conversion has taken place.

VORLAUF

Vorlauf (recirculation) should be done gently and with care so as to avoid a stuck mash. It is important to recirculate long enough to establish a good filter bed, but not so long as to compact the mash bed too much. Start off slowly, and gradually increase the recirculation rate until the wort is flowing at about your desired runoff speed. Continue recirculating until the wort is running relatively clear and free of most medium-sized grain particles. If the filter bed is not well established and the wort is not properly clarified before running to the kettle, small particles of grain and starch will be washed over to the kettle where boiling can cause haze and harsh, astringent flavors in the final beer.

LAUTERING AND SPARGING

Lautering should also be done with care. Even with the addition of rice hulls, lautering too fast can set the mash bed and lead to a long and difficult runoff. After you are satisfied with the clarity of your wort during recirculation, start lautering to the kettle at the same flow rate. When the first kernels of grain are exposed on top of the mash bed, start your sparge. The sparge water temperature should be 166–170°F (74.5–76.5°C). Do not exceed 170°F (76.5°C) or you will begin to leach tannins and husky flavors. Temperatures above 170°F (76.5°C) will also begin to wash unconverted starch over into the kettle. Keep one to two inches (2.5–5 cm) of sparge water above the grain bed. As your sparge continues and the sugars are rinsed from the grain, you can slowly increase the runoff speed. Lauter times should be around 60–90 minutes and lautering pH should be kept between 5.2 and 5.6 for an unsoured mash.

The lower starting gravity of Gose-style beers means there is not a lot of malt in your lauter tun compared to what you might be used to. You will have to be careful not to oversparge. I recommend stopping runoff when the wort runnings get to 2°P. Collecting wort after the gravity has dropped below 2°P (1.008 SG) will lead to harsh tannins, polyphenols, and husky flavors in the beer.

Detour 2: Kettle Souring

This option will be discussed in the “Souring the Beer” section below. If you plan on souring your beer in the kettle, please rejoin the rest of us after reading that section.

Figure 4.2. A selection of kettle-soured beers including Berliner weisse and Gose. Photo courtesy of Phil Cassella, Craft Beer Cellar.

THE BOIL

We boil the wort for several reasons: to sanitize it, to halt enzymatic activity, to extract hop bitterness and make it water soluble, to coagulate and precipitate proteins, and to volatilize and drive off unwanted compounds such as dimethyl sulfide (DMS). Boiling will concentrate wort flavors as water evaporates, reduce wort volume, and especially with direct-fired kettles, can caramelize sugars and add to color formation. Some white beers, Gose among them, were often not boiled for very long; some sources say as little as 10 minutes. Other later sources maintain Gose-style beers were boiled for two hours.1 How long you decide to boil will depend on what you want the boil to achieve. If you are planning on an extended boil time, you should not boil the hops for more than 60 minutes, as this can extract unwanted compounds that will negatively affect the flavor of the finished beer. Boil times of two hours or greater can actually cause some of the proteins coagulated in the first 90 minutes of the boil to disassociate, causing problems downstream.

A short boil will not thoroughly precipitate your proteins, or provide sufficient hop utilization, and may leave you with some unwanted sulfur compounds. But if you want to recreate the white Gose-style beers from the Middle Ages, a short boil may be part of your process. And because hop bitterness extraction and haze formation are of less concern with Gose than with some other beer styles, you may elect to shorten the boil time some. For brewing twenty-first century Gose-style beer, I would recommend boiling the wort as you would with your other beers. A 90-minute boil is standard for most beers, with hops added for the last 60 minutes. Wheat beers have more protein and less hops (which assist with protein coagulation), so if you are looking for a clearer Gose, you may want to consider a boil time of at least 90 minutes. Additionally, the vigor of the boil can affect all of the aforementioned activities, but especially the coagulation of proteins; the more vigorous the boil, the better the protein coagulation. With normal brewing equipment, anything less than a 45-minute boil negatively affects protein coagulation and hot break formation. Some advanced brewing systems claim the ability to accomplish both in about that time; but with more traditional kettles, a lengthier boil is recommended. Irish moss or Whirlfloc™ can and should be used if you are hoping to remove some additional proteins. But again, if you don’t coagulate proteins in an adequate boil (i.e., 45–90 minutes) then clarifying agents are less effective.

Shortening the boil time somewhat from 90 minutes may be a consideration for brewers with direct-fired kettles who want to keep color formation to a minimum. For brewers using malt extract, boil times can be shortened to as little as 30 minutes without worrying about the above issues.

Kettle Hops

Hops are usually added at three stages in the brewhouse: boiling hops for bittering; flavor hops during the last 2–30 minutes; and aroma hops after the boil, while the wort is still hot. Since Gose beers are not hop forward, brewers may elect to eliminate one, two, or even all three of these additions, although I would advise the use of enough bittering hops to adequately balance malt sweetness. The decision to eliminate a hop addition will be based on the other spices you use in the beer and/or the qualities you wish to get from the hops.

Bittering hops should be boiled for a minimum of 30 and a maximum of 60 minutes. As noted previously, boiling hops for more than 60 minutes can extract harsh and unpleasant flavors (Cantwell and Allen 1998).

The choice of a finishing hop is more subjective. Try to find aromas that are pleasing to you and that blend well with any spices that you have chosen. Hop growers and merchants will tell you that the best way to determine a hop variety’s aroma contribution is to take a hop cone or pellet and rub it vigorously between your palms, then cup your hands and smell. This method works well for both finishing hops added to the hot side and dry hops added post-fermentation, though use of the latter is not typical in traditional Gose-style beer.

If you have not already soured your beer in the mash or the kettle and you are planning on souring post-brewhouse, it is important to know that most strains of Lactobacillus are not very hop tolerant. You should know how hop tolerant your Lactobacillus strain is, and adjust the hop additions accordingly so as not to inhibit Lactobacillus growth later in the fermentor.

WHIRLPOOL AND HEAT EXCHANGE

After the boil is complete, it is important to remove the trub or hot break from your wort prior to pitching yeast. Allowing the trub to be transferred over to your fermentor can negatively impact the flavor of both wort and beer, as well as yeast vitality. Transferring too much hot break to the fermentor may also increase the production of fusel alcohols. Centrifuging your wort is an easy and effective way to remove the hot break and can be done in most kettles (except those with an internal calandria) or in a separate whirlpool vessel. In smaller brewing systems (300 gal. [9.7 bbl., or 11.4 hL] or less) getting an acceptable rotation can be achieved manually with a paddle. In larger systems you will need to use a pump, which draws wort off from the center of the vessel and pumps it back in tangentially to the side wall. This spinning of the wort will cause the heavier particulates and coagulated proteins to gather in a cone-shaped mass at the middle of the vessel’s base. The optimal rate of wort rotation is 12 to 15 revolutions per minute. Once you have achieved that rate of spin, stop stirring or recirculating the wort. The wort should be allowed to stop spinning naturally (usually that takes about 20 minutes). The clear, hot wort is drawn off from the side and sent to the heat exchanger, leaving the solids behind in the middle of the vessel. Today some breweries elect to put the wort through a mechanical centrifuge separator. Mechanical centrifugation can be faster and more effective at removing trub solids than using a whirlpool.

After separating the clear wort from the solids, cooling of the wort should happen as quickly as possible. For modern Gose, that means a heat exchange to bring the wort from around 212°F (100°C) to fermentation temperature of 66–72°F (19–22°C), depending on the yeast choice and the desired flavor profile.

It is necessary to add oxygen to the wort right after cooling. Without adequate oxygenation, the yeast will not fully attenuate the beer. This oxygen can be added using sterile filtered air, or medical-grade or aviator-grade oxygen. The recommended amount of oxygen in cooled wort is 8–10 ppm. Air is about 21 percent oxygen, so if you use sterile air, the maximum amount of oxygen that you will be able to get into solution at fermentation temperature is about 8 ppm. If you use pure oxygen, you will be able to get slightly higher amounts dissolved into the wort, but you will never need more than about 10–12 ppm. Don’t attempt to dissolve more than 12 ppm—it’s just a waste of oxygen. Henry’s law states that the solubility of a gas in a liquid is dependent on a constant temperature, the partial pressure of the gas over the liquid, the nature of the liquid, and the nature of the gas. The key parameters are temperature and pressure. At fermentation temperature, the liquid (wort) will only hold so much gas (oxygen); any extra gas will just bubble through the solution. Henry’s law will again be useful when discussing carbonation of the beer.

This is also a good point to confirm the original gravity of your wort. Starting gravities should be 9–13°P (1.036–1.053).

If you are planning on using a coolship (koelschip in Flemish/Dutch, or Kühlschiff in German) and spontaneously fermenting or naturally innoculating your Gose, here is where you take your detour. Send your clear, hot wort into a shallow, open metal (usually copper) pan. The large surface area of the pan facilitates fairly rapid cooling and acceptable oxygen pickup. The wort will cool over the next several hours. The rate of cooling will depend on many variables, including ambient temperature, coolship size, the type and thickness of the metal used to construct it, and other variables of construction. Allow the wort to sit undisturbed in the coolship for two to seven days, or until you see signs of fermentation. Once actively fermenting, you can transfer the beer into another vessel.2 Alternatively, in colder months, one can allow the beer to sit in the coolship for 12 to 24 hours and then transfer the beer into foeders or barrels, which can then be moved to a warmer location and allowed to ferment.

SOURING THE BEER

There are many methods for souring beer, some of them easier and more effective than others. Originally, Gose was a spontaneously fermented beer, as were most beers 600 or more years ago. A description in 1740 stated, “Die Gose stellt sich selber ohne Zutuung Hefe oder Ges,” or, “Gose ferments itself without the addition of yeast.”3 And this reference was a relatively recent one in the 5,000-year history of brewing. That Gose was originally a spontaneously fermented beer makes sense, since Gose is an ancient beverage originally brewed prior to a complete understanding of yeast’s part in fermentation. And although at some point in the late early Middle Ages brewers understood that “yeast,” the sludge at the bottom of the fermentation vessel, was necessary for the next batch of beer, it was not until 1680 that Van Leeuwenhoek first observed yeast under a microscope. Van Leeuwenhoek incorrectly attributed yeast to being part of the cereals used to brew beer (Nanninga 2010). It was not until the French chemist Louis Pasteur’s work of 1857 that the true nature of yeast and its part in fermentation was understood. In fact, it was Pasteur who also did the groundbreaking work on lactic acid production. He demonstrated that when different microorganisms contaminate wine lactic acid is produced, thus making the wine sour (Ligon 2002). He wrote in 1857, “I intend to establish that, just as there is an alcoholic ferment, the yeast of beer, which is found everywhere that sugar is decomposed into alcohol and carbonic acid, so also there is a particular ferment, a lactic yeast [bacteria] always present when sugar becomes lactic acid” (quoted in Manchester 2007). Yes, we brewers have a great many things to thank Louis Pasteur for.

We know that by 1910 Gose-style beers were being soured in the brewhouse as described briefly by Max Delbrück in his Illustriertes Brauerei Lexikon of that same year. Since the majority of brewers today are using some variation of brewhouse souring to produce their Gose, we will focus on those options and only later will we discuss souring through spontaneous souring and fermentation or mixed fermentations.

Souring Mash

This process is used traditionally in German breweries that want to reduce their mash pH but also want to adhere to the tenets of the Reinheitsgebot. The mash is allowed to rest 100–120°F (38–49°C) until the pH drops to the desired level, which traditionally would be 5.2–5.5, but for our purposes is as low as 3.5 pH. There are several problems associated with this method of souring for anything more than just a minor mash pH adjustment. After you have soured the mash to your desired pH, you need to be able to heat it fairly quickly to get up to the proper saccharification temperature of 148–155°F (64–68°C), either in the mash tun or kettle. Moving your mash around can be difficult if you do not have the proper equipment to do so. Done improperly, it can lead to a stuck mash or excessive lautering times. Another problem with this method of souring is that there are many types of bacteria on the grain that will also be active at that temperature. Of the many, a notable one is Enterobacter. When exposed to oxygen, Enterobacter can cause some fairly unpleasant aromas such as butyric acid. They are aerobes, and thus their effects can be reduced by attempting to exclude oxygen from the mash tun by “blanketing” the top of the mash with an inert gas, such as carbon dioxide, nitrogen, or argon. But it is not possible to exclude all the oxygen, as there is a lot of air entrained in the mash mixture itself. This oxygen clings to the grain particles and in a normal mash is beneficial, in that it helps buoy up or “float” the mash bed. If you excessively mix your mash, it is possible to reduce the air that is clinging to the grain particles and thus reduce oxygen in the mash. But the downside to overmixing is, as we have discussed, that you are then left with a much denser mash bed that is much more difficult to lauter.

Fortunately, Enterobacter do not like to function at a pH below 4.5, so another way to exclude their unpleasant aromas from the beer is to lower the mash pH as rapidly as possible. Some brewers will add some acidulated malt to the mash to expedite acidification. The lower pH will minimize Enterobacter’s impact. A brewer could also acidify the mash pH with an acid addition to the mash itself, or to the mash-in liquor. But one has to be careful, because a mash pH below 5.2 creates problems of its own, for example, denaturing mash enzymes, which can result in an incomplete saccharification of starch later in the mashing process.

Another option is to mash in at saccharification temperatures of 148–155°F (64–68°C), rest 30–90 minutes, then cool the mash down to 100–120°F (38–49°C), for an acid rest. The problem here is, how do you cool down the mash? What about the inevitable mixing of the mash as you cool it down—is it excessive? You could add cold water, but this can thin the mash too much. Using a heat exchanger can be problematic as well, as most heat exchangers are not designed for semi-solid material like mash. And I would never run unboiled, bacteria-laden wort through my main heat exchange—that would be asking for a systemic infection later on. The answer would be to have a separate heat exchanger not used for post-boil wort. And again you would have issues of excessive mixing.

So what’s a brewer to do? Not to worry, there are other, more practical ways to acidify in the brewhouse.

Kettle Souring

Kettle souring is done, as you might guess, in the brew kettle. There are several methods we will discuss a little bit later, but they all begin with the same mashing procedure as one would use with a regular beer. Once the wort is separated from the grain, it is cooled to the proper temperature, and run into the kettle. There, the brewer pitches a source of Lactobacillus into the wort, which is held at a temperature 100–120°F (38–49°C). The brewer allows the Lactobacillus to do its work until the pH drops to the desired level. At that point the wort can be boiled like a normal brew. The bacteria are killed by the heat of the boil, and the wort can be transferred for fermentation—with proper care there should be little worry of contaminating other beers.

Figure 4.4. Mango-Spruce Gose collaboration beer. Label courtesy of Freigeist Bierkultur.

The advantages of kettle souring, as opposed to post-kettle souring, are several. First, since the soured wort gets boiled before being transferred to fermentation, no live Lactobacillus is sent into the cellar. Second, it enables you to fix the level of acidity desired with a good degree of accuracy. Third, you can add a little more hop bitterness to your beer, because the usually hop-intolerant Lactobacillus has already done the souring prior to your hop additions. It is important to remember that as little as 5 IBUs can retard Lactobacillus growth, and that Gose beers are not supposed to be too hoppy.

Variations on the kettle souring methods are the source of the Lactobacillus and how you process the wort in the brewhouse. I will outline these various methods and talk about some specific breweries and how they go about souring their wort in the brewhouse. Some are more complicated than others, but each has points of interest, and pros and cons.

The Clean and Careful Method

There are quite a few breweries that use this method to produce some very good beers. Mash your grains in using your usual temperature and process. After your normal mash rest period, lauter and sparge to the kettle just like you would with a non-sour beer. Once the wort is in the kettle, you have two options. One is to bring the temperature up to 160–180°F (71–82°C) to pasteurize the wort. Be sure to keep recirculating so as to be sure it is thoroughly homogenized. Your other option is to bring the wort to a boil for 5 to 10 minutes to pasteurize it. This pasteurization step does add a bit of time to the process, but brewers do it for two reasons. First is to assure that all the “bad” bacteria that was on the grain has been killed off. The second is that heating, especially boiling, helps drive out some of the oxygen in the wort. After you heat the wort, let it rest for a few minutes. This assures pasteurization and allows you some time to get everything else set up. This pasteurizing of the wort is why I call this the “clean and careful method”—you start off with sanitary wort. This method produces a cleaner flavor profile. If you decide to forego this step, you may get a little bit more funk in your final beer, but it might not be the funk you want.

At this point you will have to lower the temperature to one that is conducive to Lactobacillus growth. This is done by running the hot wort through a heat exchanger. You may choose to execute Option 1 here (see “Other Operational Options” sidebar). Monitor the temperature of the wort as it decreases. When the temperature reaches about 130°F (54°C), take a pH reading. You may want to exercise Option 2 (below) at this point. It is very important to remember to adjust your wort sample temperature before measuring its pH. As discussed earlier, pH drops as temperature rises, so a sample at 180°F (82°C) will read a lower pH (higher acidity) than the same sample at 120°F (49°C). The wort will be at the proper temperature in the kettle usually between 100°F and 120°F (38–49°C), but consult with your Lactobacillus supplier, as it varies depending on strain. You have reached the optimal temperature for Lactobacillus growth.

Now that you have made it to this point, you have some other options. These are the different ways to start souring the wort.

Method 1: Sour with uncrushed grain (pale or Pilsner malt is best) so as not to add color or flavor to the wort. Most brewers use 0.5–2 lb. (225–910 g) of grain per barrel (1.17 hL) of beer. Put the malt in a mesh bag or purpose-built stainless steel screen basket. Lower it into the wort and allow the grain to steep. Take periodic pH readings until you reach your desired pH (usually 3.2–3.6). This method usually takes 35–55 hours to sour. For faster souring times, one would need to use substantially more grain, probably at a rate of 5–10 lb. per barrel (2.27–4.54 kg/1.17 hL). See “Sauergut” sidebar for more details.

Method 2: Sour with plain, live-culture yogurt, containing L. acidophilus and possibly other Lactobacillus strains. A surprising number of brewers use yogurt to sour their wort. It certainly gets the job done and I have tasted many great beers soured with yogurt. But, I have two concerns with this method. The first regards the bacteria used in making yogurt. When souring milk to produce yogurt, dairies often uses different strains of other bacteria and with strains of Lactobacillus to do their work. For example, many yogurts include the bacteria Streptococcus thermophiles along with L. bulgaricus (Hui 2004). Some dairies use other strains of Lactobacillus. Dairies may change the strains of bacteria they use without notice. There is also some use of genetically modified (GMO) strains of bacteria in yogurt production. I like to know what strains I am adding to my wort and have more control over that choice. Different strains of bacteria will behave differently and that in turn will produce different flavors. These variations may be minor, but they may not be. I am also not sure I want Streptococcus thermophiles in my beer at all. The other concern is the lactose that I would be adding to my beer. To get a good pitching rate for a rapid souring, one has to pitch a lot of yogurt and this may lead to flavor issues. Also, your beer is no longer lactose free (if one worries about such things). But again, maybe these worries are really non-issues—the proof is in the pudding (or beer)—but they are worth considering.

Figure 4.5. Modern Times flowchart. The pH will rise during lautering if your water is above the mash pH of 5.5 (by Palmer and Kaminski 2013). Image courtesy of Modern Times Beer.

Important: Please note that the addition of yogurt in the brewing of beer is not listed on the Tax and Trade Bureau (TTB) list of, “Exempt Ingredients and Processes Determined to be Traditional Under TTB Ruling 2015–1,” and as such would require formula submission and approval by TTB prior to use in the brewing process. Consider that yogurt/dairy products/lactose are allergens to many; accordingly, a brewer should consider adding an allergen warning to the beer label. Current regulations under the Federal Alcohol Administration Act do not require the disclosure of major food allergens on alcohol beverage labels. Major food allergens used in the production of a malt beverage product may, on a voluntary basis, be declared on any label affixed to the container. However, if any one major food allergen is voluntarily declared, all major food allergens used in production of the malt beverage product, including major food allergens used as fining or processing agents, must be declared, except when covered by a petition for exemption approved by the appropriate TTB officer.

Method 3: Sour with live probiotics. There are live, non-dairy probiotics available that contain L. plantarum and other strains. Some brewers use these to add lactic acid bacteria (LAB) to their wort for souring. Advantages to using them are that they are easily available, pharmaceutical grade, and do not have other matter as a media, as does yogurt.

Method 4: Pure-strain LAB pitch. For this option you have choices too. There are five or six main strains of Lactobacillus to choose from: L. brevis, L. delbrueckii, L. acidophilus, L. plantarum, L. bulgaricus, and L. casei. These pure culture strains should be available from your local yeast supplier. Your choice of Lactobacillus strain will depend on what you want from the strain. Actually, there are over a 150 strains of LAB to choose from, depending on how far down that rabbit hole you want to go, and the variety of LAB you pitch can have some pretty interesting effects on the beer you brew. For more on Lactobacillus, see the “Bacterial Souring Agents” section in chapter 3.

Figure 4.6. Salt of the Earth Gose beer brewed with coriander and truffle salt by The Bruery in Placentia, Orange County, California.

Pitching rates for all these methods can vary greatly. We have found that for a fast pH drop (6–8 hours) you will need to achieve a pitching rate of approximately 1 × 108 cells per mL (100,000,000 cells/mL) of lactic bacteria. A pitching rate of about 1 × 106 cells/mL takes about 18–22 hours. Brewers pitching less bacteria than stated above will experience longer times to achieve the desired pH. Once the pH drops below about 4.5, it is safe from contamination by harmful bacteria or molds. Wort left to sour for more than 48 hours can be risky. If the pH is still above 4.5 after 48 hours, I would recommend dumping the wort and starting over again.

For all the above methods you will need to take pH readings to confirm that your bacteria are working, and be sure to take more frequent pH readings as you approach your desired level of acidity so that you do not over-sour your beer.

Anderson Valley Brewing Company Method

At Anderson Valley Brewing Company (AVBC) we have developed what I think is the simplest way to achieve a good and consistent souring of the wort. It produces a clean, sharp, well-defined sourness in a short period of time. The AVBC method differs in a several ways from the Clean and Careful Method.

We mash the grains as per a normal brew. After a 60-minute rest, we recirculate the wort until it clears—this usually takes about 20 to 30 minutes. We then proceed with runoff into the kettle, leaving the spent grain behind. We believe getting the wort off the grain is important, as the grain contains a lot of bacteria: the Lactobacillus that we want, as well as some other bacteria that can produce those unpleasant flavors and aromas. As the kettle fills, we introduce an inert gas, usually argon,4 into the kettle. This helps exclude oxygen from the top layer of the wort. We do this by putting a 3/8th-inch hose (~1 cm) through the kettle door and flowing argon in at a rate of about 1–2 psi (6.9–13.8 kPa). When runoff is nearing completion, we take a temperature reading. It is usually about 145°F (63°C). We then make a temperature adjustment by adding chilled house water to bring the wort down to a temperature of about 120°F (49°C).

It should be noted here that we have made a high-gravity brew, which allows us to easily cool the kettle wort with chilled water. At this point, with the wort at optimum temperature for Lactobacillus growth, we pitch a substantial amount of bacteria. This pitch has previously been grown up from a lab sample acquired from our friendly yeast and bacteria supplier, White Labs. Our propagated LAB pitch is about 2 bbl. (2.35 hL) of bacteria at 1 × 108 cells/mL. This two-barrel pitch is for about 115 bbl. (135 hL) of hot, unboiled wort—somewhat less than two percent of the total. The 115 bbl. of hot wort ends up being about 100 bbl. (117 hL) of cooled wort for the fermentor after the boil, accounting for approximately 11 percent boil evaporation and four percent shrinkage from cooling.

We continue the argon “sparge” for the duration of the souring process. We monitor the pH drop over the next 6 to 12 hours, six hours being very fast for us, and 12 hours being on the long side.

Figure 4.7. A Lactobacillus propagation on a hemocytometer under the microscope. As you can see from the photo, it can be very difficult to count bacteria at the proper pitching rate. Photo by Federico Guazzone.

If we are producing a double batch of approximately 200 bbl. (235 hL), when the pH reaches around 3.9 we know that the growth phase of the Lactobacillus is nearly finished. We then pull off 15 bbl. (17.6 hL) from kettle #1 and transfer it to kettle #2, which has been waiting with about 85 bbl. (100 hL) of fresh, unsoured Gose wort at 122°F (50°C). The amount of bacteria is somewhat lower in the 15-bbl. pitch than it was in the 2-bbl. pitch, hence the larger amount. We continue to monitor kettle #1 until it reaches a pH of 3.4.

Once the pH reaches 3.4, we bring the wort to a boil and proceed as with any other beer. We continue to monitor kettle #2 until it too reaches 3.4, or sometimes a bit lower depending on the pH of the first batch, and then we proceed to boil.

When the wort has boiled for 60 minutes, it is completely sterilized and we can proceed to the whirlpool. Once the whirlpool is full and spinning at 12 rpm or faster, we allow the wort rotation to come to a stop. This usually takes about 20 minutes. When the whirlpool is finished, we then proceed to cool the wort to 68°F (20°C).

We ferment the beer with our house yeast, which is an English ale variety. Our house yeast has no problem fermenting at that pH. Some yeast strains will not do as well with a pH that low. Be mindful of the yeast you use to brew your Gose, and be sure it can tolerate the acidity of Gose wort and still produce good flavors.

Figure 4.8. The Kimmie, the Yink, and the Holy Gose Ale by Anderson Valley Brewing Company in California.

The main advantages of the AVBC method is that it is easy, produces good acidity, is relatively fast, gets the wort off of the grain to contain undesirable bacteria, and has a low risk of infecting our other beers.

The main disadvantage of the ABVC method is that once our yeast has finished fermenting a Gose, it cannot be repitched in any other house beers. Our house yeast produces nice flavors at pH levels as low as 3.1, but yeast harvested and repitched from our Gose never makes acceptable tasting beer again. The house yeast from a Gose ferment is essentially burned-out by the low pH. In the beginning, this was not a problem for us, but as we produce more and more Gose-style beers it has become an issue we have had to address. We now have to propagate more yeast than we used to. Another less worrisome issue is that we spend a fair amount of time and effort propping up Lactobacillus bacteria so that we can have a large, healthy pitch. I have been told by some brewers that the yeast they use to brew their Gose-style beers can be repitched without any difficulties. I would assume that the question of whether or not a yeast is affected by the low pH of a Gose is strain-specific, and also related to how low of a pH wort it had to ferment.

Alternative Method

Some brewers do a normal mash and runoff to the kettle, cool the wort through a heat exchanger or by adding cold water until it reaches 122°F (50°C) and then just let the wort rest without further assistance. They figure that there is enough souring bacteria on the grain that has carried over to the wort, which is true to some degree. But the amount of Lactobacillus bacteria coming over in the wort from your mash is not really sufficient for rapid souring—and I recommend a fairly rapid souring. Souring by this slower method can take up to two or even three days to sour to an appropriate pH of 3.6 or lower. For most breweries, three days is too long a time to wait to sour a beer, and this long period of time can also allow other bacteria that were on the grain to produce off-flavors. But brewers who use this method say they do not want to add yogurt or pitch extraneous bacteria culture. They want just what’s on the grain.

High-Acidity Brewing

This method requires a separate area for making a high-acidity brew of Lactobacillus-soured wort. The high-acidity wort is then injected into a regular, unsoured brew in the kettle. Then the whole kettle is boiled to sterilize the wort so that the soured wort addition doesn’t further acidify the rest of the batch. The brewer relies on getting the initial sour wort to an extremely high level of acidity, then blending at a set ratio of 25 percent soured wort to 75 percent sweet, unsoured wort to hit the target final acidity in the fermentor. Souring bacteria for the high-acidity wort can come from any of the sources mentioned above, although a straight pitch of Lactobacillus, especially strains with a high acidity tolerance, would work best. This method is very similar to the method Sierra Nevada uses to make their award-winning Otra Vez Gose.

Figure 4.9. Otra Vez, a Gose-style ale brewed with cactus and grapefruit by Sierra Nevada Brewing Co., Chico, California.

Conclusions to Using Bacteria as a Souring Agent

After much research, discussion with many brewers, reading many articles, and tasting many brewhouse-soured beers, I think that the biggest issue of using bacteria as a souring agent is the potential for off-flavors and aromas produced by aerobic bacteria. These flavors and aromas result from the development of isovaleric acid (dirty gym socks), butyric acid (vomit), and in some cases an excess of acetic acid (vinegar). These flavors and aromas are not produced by Lactobacillus, even in the presence of oxygen. The best options for avoiding these undesirable flavors are to keep non-lactic acid bacteria from metabolizing sugars by: 1) excluding oxygen; 2) dropping the pH below 5.0 as fast as possible;5 and 3) pitching a sufficient amount of Lactobacillus. It is also critical to get the wort off the grain as soon as possible, because the grain has a lot of those other bacteria on it, and, as we’ve discussed, a normal grain bed holds in little pockets of air, and oxygen in that air allows undesirable bacteria to do their thing.

Some Non-Bacterial Souring Options

For brewers who do not want, for whatever reason, to go through the process of a bacterial fermentation, there are other options.

Lactic Acid Addition

One can simply add lactic acid to the wort or beer. The advantage of this method of souring is that it is simple. It can even be done post-fermentation, thus leaving your yeast happy and healthy, and there is no danger of infecting any of your other beers with that pesky Lactobacillus. Unfortunately, there can be several problems associated with this method of souring your beer. The flavor is not the same as a bacterial fermentation; many people, myself included, assert that sour beers made this way are less complex. They do not have the depth of flavor that I hope to taste in a Gose. Also, concentrated lactic acid can be very syrupy and it can be very hard to mix into wort or beer, especially in cold, finished beer. For that reason, I recommend that you avoid mixing lactic acid concentrate into cold beer. Finally, it is not considered a very artisanal method of souring, and, in my experience, consumers frown on these sorts of additions to their craft beers. So this method may leave you with a bit of a marketing hot potato.

Acidulated Malts

Acidulated malts can be added to the grain bill to bring the pH down. The advantage to this souring method is that it is very easy, and since no live bacteria are involved there is no greater risk of infecting other beers than you would have with a regular mash. The disadvantage to this method is that it does not bring the pH down as much as some brewers would like; that is, unless you use a prodigious amount of acidulated malt, and this has flavor impacts that most people would find undesirable. Finally, this type of acidifying in the brewhouse leaves the brewer with the potential pitfall of subjecting the house yeast to an acidified wort to ferment. To drop the pH of the mash from 5.2 to 4.2, add approximately 8–15 percent acidulated malt to your total grist bill.

A combination of two or more of the above methods can be used to create a process unique to a brewery and thus add an acidity level that fits the brewery and the beer. For example, one could use a small portion of acidulated malt, do a brief kettle souring, and then add a little bit of lactic acid in the fermented beer to touch up the acidity. In the end it is all about finding the method or methods that work best to create the beer a brewer wants to brew.

Lactobacillus and Mixed Fermentations

For the very brave brewers out there—or for those producing sour beers exclusively—there is the opportunity to sour your beer in a more traditional way. This would be what is called a mixed fermentation. Mixed fermentation can refer to multiple yeast strains or multiple bacteria strains, but typically it refers to a fermentation with brewer’s yeast and bacteria together. There are several options for mixed fermentation. A brewer could start with souring their wort in the brewhouse and then transferring the live, actively souring wort to the cellar, allowing the bacteria to continue to work during the main fermentation with pitched yeast. Or you could make a non-sour wort and then allow for a mixed culture fermentation in the cellar, featuring both yeast and either LAB or other microorganisms. The latter would be the more traditional way, and closer to how a Gose might have been made during the Middle Ages.

If you have transferred brewhouse-soured beer over into your cellar, all you would need to do would be to cool the wort to fermentation temperature and pitch your desired yeast strain. If you choose the more challenging, traditional method of a completely mixed fermentation, you could pitch a known bacteria and a known pure-culture yeast strain into your cooled wort; this would help to ensure unwanted bacteria and avoid off-flavors. Or you could let the microorganisms fall where they may and have a completely spontaneous fermentation. In either of the latter cases, it is best to have an IBU level less than 10 and preferably less than 6.

Should you decide to try out one of these methods, you should certainly keep in mind that fermenting with and growing up bacteria in a “clean” beer brewery has some serious dangers. Isolation of the sour beer and rigorous sanitation procedures need to be followed throughout the whole process so as not to spread microorganisms and contaminate your clean beers and yeast strain.

Some Potential Effects of a Mixed Fermentation

The presence of lactic acid can be a yeast stressor, so much so that the presence of Lactobacillus can stall or slow some yeast fermentations. This is likely the result of a combination of low pH and the ability of lactic acid (both L-lactic acid and D-lactic acid) to change the way yeast ferments. In a normal fermentation, the yeast will ferment glucose first before any other sugars. In the presence of high levels of acid, usually below a pH of 4.0, yeast may consume multiple types of sugars regardless of whether glucose is present or not. The presence of high levels of lactic acid has been shown to be responsible for stuck wine fermentations as far back as Louis Pasteur’s time. This effect, known as “terminal acid shock,” can affect some species of Saccharomyces cerevisiae and Brettanomyces bruxellensis.8

This presents a challenge to brewers making brewhouse-soured beers, or if they are planning on bottle conditioning those sour beers. Although yeast after sour fermentation may be around 80 percent viable, the surviving cells are small and are not budding. This indicates that they are not healthy and have ceased growing and entered the dormant phase.

Another consideration when doing a mixed fermentation is that some yeast strains can have similar effects on LAB. A study done by Hübbe showed that when L. brevis and L. parabrevis were co-fermented with Brettanomyces, the cell count of L. brevis was reduced by about 50 percent compared to when it was grown by itself, and that the growth rate of L. parabrevis was reduced even further, to as low as 15–20 percent of normal (Hübbe 2016). When co-fermented with both Brettanomyces and S. cerevisiae, the Lactobacillus growth was further diminished to between 2 and 13 percent of normal cell growth without competition. This shows that when used in a mixed fermentation, one can expect the activity of some species of LAB to be affected negatively and dramatically, and that the ability of Lactobacillus to compete with Brettanomyces appears to be species dependent. Interestingly, Brettanomyces activity was not affected by the presence of Lactobacillus, as some Saccharomyces strains are, but Brettanomyces was affected by the presence of S. cerevisiae in a mixed fermentation in low oxygen or anaerobic conditions.

One option to consider when using mixed fermentation is extended aging time. During a mixed fermentation not all the microorganisms hit their stride at the same time. For the most part, each yeast or bacteria will have its turn making use of the available energy sources. This will be very different depending on what mix is in your culture, but suffice it to say that these fermentations can take significantly longer than “clean beer” or brewhouse-soured beer fermentations. Extended aging times can be as short as two months for a piquant saison or as long as two to three years for complex barrel-aged beers. One reason for this is that some microorganisms can create off-flavors, such as sulfur compounds, that may take weeks or even months to be metabolized by other organisms. During aging, regardless of the nature of the vessels the beer resides in, it should be kept below 80°F (26.5°C) and above 55°F (13°C). Several brewers believe that the sweet spot is about 65°F (18°C).

It is safe to say mixed fermentations are more complicated than producing conventional “clean” beer or brewhouse-soured beers. If you are planning to go down the mixed fermentation path, I would suggest exploring the Milk the Funk Wiki9 and reading American Sour Beers by Michael Tonsmeire.

The first anxiety-causing aspect of brewing your first sour beer is not time, variability, or even the risk of bad beer—it is the fear that the ‘wild’ microbes will ruin other batches of clean beer. This is a legitimate concern.

—Michael Tonsmeire, American Sour Beers (Boulder: Brewers Publications, 2014), 16

CLEANING AND SANITATION

If you are using bacteria to create sourness in your Gose, then you will need to take some extra sanitation precautions. Of course, you will need to take all the normal precautions you would with any other beer so as not to infect it with unwanted bacteria or wild yeast—that is just good brewing practice. But when using wort- and beer-souring bacteria, you need extra special precautions. If you make the decision to intentionally bring souring bacteria into your brewery, that decision should be accompanied by a solid understanding of what consequences could come from it. Lactobacillus and Pediococcus are usually the brewer’s sworn enemies. They must be kept completely separate from the main part of your non-sour brewing operations and all your other non-sour beers.

It is important to understand and remember that bacteria and wild yeast are able to metabolize dextrins and other carbohydrates that normal brewer’s yeast cannot, and that it takes far fewer bacteria or wild yeast to have an impact on your beer’s flavor. Bacteria and some wild yeast are also smaller than normal yeast and are thus able to “hide” and remain lodged in soil or crevices in areas that some sanitizers might not be able to get to. For all these reasons, great care must be taken to eliminate these microorganisms from your equipment before introducing your wort to it if you hope to make acceptable beer repeatedly.

When comparing brewhouse souring with mixed or spontaneous fermentation, brewhouse souring is the safer option. Brewhouse souring keeps all the LAB on the hot side of your operation. If at all possible, your brewhouse operations should be kept physically separated from your cellar operations. This is good brewing practice for any brewery, because milling and mashing can give rise to a lot of malt dust in the air. Malt dust contains LAB that will sour your beer. I know that in some smaller breweries the separation of the brewhouse and the cellar operations is not always possible. Those brewers should give serious consideration to partitioning the two operations. If you cannot, you will need to take extra steps to keep your non-sour beers safe from souring bacteria. Special care should be taken with any equipment that is used to propagate or transfer LAB. Be sure to permanently mark all the equipment that you use for sour beers. This will help ensure that you keep the equipment separate from your non-sour beers equipment. At Anderson Valley, we are fortunate that our brewhouse is in a separate building. Anything used in souring wort or beer remains outside of our cellar building and packaging hall. We use a whole separate set of hoses, pumps, clamps, gaskets and tanks for culturing and transferring our Lactobacillus and non-sterilized sour beers. This is especially important for soft goods like hoses and clamps. We never mix our sour-designated equipment with our clean beer equipment. The only piece of equipment that gets used for both sour and non-sour beers is the boiling kettle. Once the wort has been boiled for 60 minutes, we consider it clean and sanitary and only then can it pass over into the cellar. Some breweries even go so far as to have their brewers change boots and gloves between their sour and non-sour operations.

If you decide you would like to go the more traditional route of souring your Gose post-brewhouse, I would recommend that you take extraordinary care. I would recommend you not only separate sour equipment from non-sour, but that you pitch and ferment in a separate, designated sour building. Many breweries have taken this approach: Firestone Walker’s sour and non-sour facilities have different zip codes; The Bruery’s two breweries are now separated by several miles; Anderson Valley uses two different buildings separated by over an acre. Trying to run a clean beer and sour beer operation in the same building can only lead to trouble. There is ample evidence of this, but one of the best-documented recent cases is that of The Bruery. After their issues arose, The Bruery separated their sour from non-sour beer programs and this, along with vigilant quality assurance and quality control (QA/QC) measures, has resolved the issue. Their honest transparency about it is to be applauded, as are the great lengths to which they went to rectify the problems. You can read about it on The Bruery’s website.10

Cleaning

You will need to thoroughly clean and sanitize your equipment before and after every brew. Remember that you cannot properly sanitize equipment that is not first properly cleaned. If the equipment is not clean, you are leaving a place for unwanted bacterial and wild yeast to hide and grow. If your equipment is not clean, the soil on it may neutralize the sanitizer you are using. Clean your equipment and then sanitize it. Equipment should be cleaned with an appropriate agent to remove organic soils (trisodium phosphate, sodium hydroxide, Bru-R-Ez, Five Star PBWTM, or similar products). Equipment should also be periodically cleaned with an acid-based cleaner to help remove any beerstone buildup. This is especially true of equipment used for post-fermentation beer. Beerstone is not broken down by traditional alkaline cleaners—you need an acid-based cleaner. Always follow the manufacturer’s instruction when using cleaners. Adding more chemicals to your cleaning solution does not clean better, and in some cases can clean worse. Always wear the appropriate personal protective equipment (PPE) including gloves, safety glasses, footwear, chemical-resistant aprons, and face shields. Some people think that my concerns about cleaning are excessive. Maybe they are. But unless you want to make random, unrepeatable beers (though they certainly can have their place) you need to start with a clean slate every time—even if you are spontaneously fermenting your beer. To get a clean slate, you need to properly clean and sanitize your equipment.

Sanitation

Heat

There are several ways to sanitize your equipment. The best sanitizer is heat, preferably steam. Bacteria are very small and can hide in tiny cracks, or crevices in your equipment, especially in cracked hoses and gaskets. Heat gets to places other sanitizers cannot, and can penetrate those tiny crevices, cracks or scratches that other types of sanitizer might not be able to. With adequate heat, almost all known life-forms can be eliminated. But heat is dangerous, and it is hard on all your equipment, especially soft goods like hoses, gaskets, and plastic. Even stainless steel suffers when it is repeatedly heated and cooled over time. Great care should be taken if using heat with any sort of pressure. Heat plus pressure can be explosive, and pressurized hot liquid can remove skin instantly. Most brewers who use heat keep the temperature below 185°F (85°C).

Acid

Other brewers prefer to use an acid-based sanitizer. These sanitizers are safer, but are not as effective as heat. There are many options for acid-based sanitizers. Discuss with your local suppliers what options are open to you and which are best for you. There are also acid-based sanitizers with added iodine that can be more effective than solely acid-based sanitizers, but they have two main drawbacks. First, they lose their efficacy fairly quickly (18–48 hours) once prepared, and second, they can taint beer and cause off flavors, even when used at the recommended concentration. I have found it useful to occasionally change up sanitizers, as wild yeast and bacteria can occasionally build up resistance over time to a specific sanitizer. For all your cleaners and sanitizers, always follow the manufacturer-recommended instructions and safety procedures.

1 Jürgen Reuß, “Die Goslarer Gose,” Bier aus eigener Küche (website), September 28, 2004, http://​www.bierauseigenerkueche.de/​Goslarer%20Gose.html

2 http://​www.milkthefunk.com/​wiki/​Coolship and http://​www.milkthefunk.com/​wiki/​Spontaneous_​Fermentation#Cooling

3 Wikipedia contributors. “Gose” Wikipedia, The Free Encyclopedia. https://​en.wikipedia.org/​w/​index.php?title=Gose&oldid=845794675. (accessed June 15, 2018).

4 When using any gas in an attempt to exclude oxygen from an environment, it is imperative that you do not subject yourself or others to that environment. Argon and carbon dioxide will all displace oxygen and in doing so can cause asphyxiation. So when using these gases to evacuate oxygen from the kettle, it should be done in an area that is adequately ventilated with outside air.

5 Most of the unwanted bacteria will not, or in some cases cannot, carry out life functions (and produce unwanted metabolites) at a pH lower than five.

6 You want to exclude oxygen here in the case of contamination from other unwanted bacteria. Oxygen doesn’t significantly affect most species of Lactobacillus. Most varieties will grow and produce lactic acid regardless of the presence or lack of oxygen. They will not produce significant amounts of butyric or isovaleric acids in the presence of oxygen either, although some species may produce small amounts of acetic acid in aerobic conditions.

7 L.C. Peyer et al., “Growth Study, Metabolite Development, and Organoleptic Profile of a Malt-Based Substrate Fermented by Lactic Acid Bacteria,” J. Am. Soc. Brew. Chem. 73, no.4 (2015): 303, http://​dx.doi.org/​10.1094/​ASBCJ-2015-0811-01.

8 Milk the Funk Wiki, s.v. “Lactobacillus,” last modified May 26, 2018, 17:35, http://​www.milkthefunk.com/​wiki/​Lactobacillus.

9 Milk the Funk Wiki, s.v. “Mixed Fermentation,” last modified May 16, 2018, 16:31, http://​www.milkthefunk.com/​wiki/​Mixed_​Fermentation.

10 Cleaning the slate—beer issues from 2013,” The Bruery (website), December 23, 2013, http://​www.thebruery.com/​cleaning-the-slate-beer-issues-from-2013/.

11 Stainless steel can be scratched or damaged. It is important that all your brewing staff know which scouring pads, or “scrubbies,” are safe to use on stainless. Only white scrubbies are soft enough to use and will not scratch stainless steel. Green scrubbies are a bit harder; they will scratch stainless, and so should never be used for cleaning interior stainless surfaces. Red scrubbies are meant to be abrasive and cause fairly deep scratches on stainless steel, which may result in rusting.

12 “Guidelines for Alloy Selection for Waters and Waste Water Service,” Nickel Institute (website), last accessed June 9, 2018, https://​www.nickelinstitute.org/​NickelUseInSociety/​MaterialsSelectionAndUse/​Water/​AlloySelection.aspx.

13 The average life of a 316 stainless steel fermentor is about 30–50 years depending on the number of cycles it sees and the temperature and type of chemicals used in the hot CIP. The average life of a 304 stainless steel kettle is about 20–30 years depending on similar variables. These estimates are for equipment not making sour salty beers.