The two main components of the ferments in this book are milk (dairy or plant) and microbial cultures. To the purist, the term milk applies only to the secretions of the mammary gland, but many food companies and consumers also call whitish liquids extracted from plants — such as coconuts and soybeans — milk. In this book, if the source of the milk isn’t a mammary gland, I’ll define the provenance, such as almond milk, and in no situation will I use the term dairy to describe a product derived from a field of soybeans or a coconut grove.
All milk seems to be the same at first glance — white, liquid, and available at every corner market and gas station in the United States — but practice and research tell us that not all milks are created equal. Milk ferments are only as good as the milk used to make them.
Dairy Milk
The best milk for fermentation comes straight from the animal and is never chilled, homogenized, packaged, or transported. One of my favorite truisms is “milk was never designed to see the light of day.” In other words, nature designed milk to go straight from the mother’s teat into the mouth and then the stomach of her infant, where it is immediately acidified and curdled. Each step we add in our attempt to preserve milk as a drinking liquid decreases its quality and character. The closest you can come to mimicking nature is to take the milk from the animal and immediately ferment it into yogurt, kefir, or cheese — much like the young mammal’s own stomach would do.
The most common sources for dairy milk are cows and goats. Sheep’s milk is rarely available for purchase but of course can be produced at home, and water buffalo milk is even harder to find — as are water buffaloes! Even if you don’t get a chance to make your own dairy ferments from sheep or water buffalo milk, it’s definitely worth sampling commercial varieties when you find them. Each type of milk has its own peculiarities when it comes to selecting and working with it.
Cow’s milk is the most common type of dairy milk in the Western Hemisphere; cows definitely hold the title of dairy queen when it comes to the volume of milk produced and used. You’ll have many choices when it comes to choosing cow’s milk (more on that in Keeping It Fresh), but one of the most unique differences is the characteristic of “creaming” — when the fat globules cluster together and rise to the top. When using whole, nonhomogenized milk for dairy ferments, you’ll end up with a luscious, heavy layer of cream on top. Milk from pasture-reaised cows is also typically more yellow because the beta-carotene cows eat when grazing on healthy pastures lends its red-orange pigment to the milk. (Our bodies convert beta-carotene into vitamin A.) Goats, sheep, and water buffalo convert beta-carotene into vitamin A before it becomes a part of the milk, making their milk much snowier in hue.
Goat’s milk fat is very delicate and prone to damage that quickly alters the flavor of the milk and can make it taste “goaty.” Fresh goat’s milk that has been handled properly, however, will be clean-tasting and free from musky or barnyard notes. The milk from many types of goat breeds will produce a rather thin yogurt due to its type of protein and fat content. The milk from Nigerian Dwarf, Nubian, and LaMancha goats typically has more of the right kind of protein, and Nigerian Dwarf and Nubian milk has a higher butterfat content as well, making the milk of either breed a wonderful choice for naturally thick yogurt and kefir. Goat’s milk lacks a particular protein (cryoglobulin), present in cow’s milk, that causes the fat globules to clump together and rise to the top, giving it a smooth mouthfeel.
Sheep’s milk, too, should be clean and pure tasting, but sometimes it is contaminated by lanolin, a waxy substance naturally found in sheep’s wool. Lanolin can be present on the animal’s udder and accidentally collected during milking, giving the milk and any products made from it an unappealing flavor and tacky mouthfeel. Yogurt and kefir made from high-quality sheep’s milk is usually very thick and rich, thanks to its high levels of fat and protein, as well as the type of protein it contains. As with goat’s milk, the cream will not separate readily from sheep’s milk.
Water buffalo’s milk makes amazingly rich yogurt. Years ago, I had some made by the former Woodstock Water Buffalo in Vermont. I remember it being the most exquisite yogurt I’d ever had. The richness of water buffalo’s milk is unsurpassed. I’ve heard that yak’s milk is similar, but the cream will separate, unlike water buffalo’s milk.
Keeping It Fresh
Always remember that aforementioned truism: milk was never meant to see the light of day. Yet the reality of dairy production means that refrigeration and storage are essential. So what do dairy fermenters need to know about their milk and milk source in order to feel comfortable making products for their family and friends?
Store-Bought Milk
Most home dairy fermenters will likely work with store-bought milk. Fortunately, most processed grocery-store milk can be turned into some darned good fermented products. When buying milk at the store, you’ll have some information to consider: expiration date (choose the freshest); whether it is ultra-pasteurized, pasteurized, or raw (if you happen to live in a state where it is legal to buy raw milk in a store or from a farmer); fat content (fat-free, 1 percent, 2 percent, or whole); homogenized or cream-top; if it is certified organic; any fortification with vitamins or other nutrients; and whatever marketing terms the company is using to describe its production, such as whether the cows were grass-fed.
We’ll cover various heat treatments in chapter 4, but in general, all store-bought milk has been pasteurized. Ultra-pasteurized milk has been heated to a higher temperature, which results in the longest shelf life. Unfortunately this heat treatment also changes the milk proteins and their suitability for making some milk products. While you wouldn’t use ultra-pasteurized milk for cheesemaking, you can use it to make yogurt and kefir, and in fact, it will save you a step in the process! (More on that in chapter 8.) Raw milk, where available, has had no heat treatment but often has been produced under some sort of regulatory oversight.
Commercially produced cow’s milk is almost always standardized to a set fat content — whole milk to between 3.2 and 3.5 percent butterfat, and skim to between 0.1 and 0.2 percent. Most cow’s milk is also put through a mechanical process called homogenization, which disrupts the fat globules so that they will no longer separate and float to the surface. Only nonhomogenized, cream-top milk is certainly whole milk — that is, it has the natural fat content produced by the animal. (Goat’s, sheep’s, and water buffalo’s milk usually has all of its natural fat content due to its natural state of incorporation.) Unless a recipe specifies a particular fat content, you can use whatever type of milk that you prefer. The higher the fat content, though, the creamier the texture. I’m a believer in full-fat milk, as the vitamins contained in the milk fat globules help our bodies absorb the nutrition in the milk. Thankfully, the medical and science community is again embracing the healthy aspects of full-fat dairy!
Most commercial milk is also fortified with vitamin D, which is added as a way to make up for the vitamin D that is lost when natural fat is removed as part of the standardization process; it also makes up for a typical lack in the average diet. Some milk is also fortified with vitamin A or omega-3 fatty acids — usually in the form of fish oil. Neither vitamin D nor omega-3 fortification will harm milk fermentation. Milk labeled as grass-fed or organic is the most likely to be naturally higher in beta-carotene and have the resulting golden color, compared to the milk from cows fed in total confinement.
Redwood Hill Farm & Creamery
Sebastopol, California
I’ve been lucky enough to know Jennifer Bice, founder and former CEO of Redwood Hill Farm & Creamery, for over a decade. Goats bring a lot of people together, and thanks to magnanimous, kind people like Jennifer, the goat world is a better place. Perhaps even more importantly, the rest of the world is a better place thanks to Redwood Hill Farm & Creamery’s pioneering goat milk products.
In 1970, Redwood Hill Farm, founded by Jennifer’s parents in the 1960s, debuted the nation’s first goat’s milk kefir. They chose kefir because its drinkable consistency works well with goat milk and it was a perfect fit for the health-conscious San Francisco Bay Area customers. However, at the time most Americans had barely heard of yogurt, never mind kefir. The product was eventually discontinued, albeit with a small, loyal following. Jennifer remembers loving it as a kid. “It was thick and like a milkshake,” she says.
In 1978, Jennifer and her husband, Steven Schack, a fellow goat aficionado, assumed leadership of the struggling farm and dairy. Jennifer was still in college at the time, but the couple wanted to find a way to produce income and keep their goats, so they focused on expanding the milk business. The revival of the farm was a success. In 1982, they launched the first commercially produced goat’s milk yogurt in the United States. By this time, more people were aware of the health benefits of yogurt. In addition, Redwood Hill Farm had an existing solid customer base and distribution network for its milk, which helped jump-start a viable goat’s milk yogurt market.
In order to craft a thick product that customers would find appealing and would hold up to transport through the market distribution chain, the couple turned to Jennifer’s brother, Kevin Bice. Kevin was pursuing a dairy science degree at Cal Poly and had experimented with many different ingredients for thickening yogurt. He formulated the use of tapioca starch, from cassava root, to create the perfect thickness in the yogurt, without any flavor change or added allergens. (Tapioca starch is my thickener of choice as well; see how to use tapioca starch in your recipes in the table.)
For 18 years, Redwood Hill Farm used the services of a co-packer to fill and incubate their yogurt in the cup for them. In 2004, the company built their current spacious, state-of-the-art facility in Sebastapol for producing the yogurt from start to finish. In a smart move, they built it too large. Within a few years, an organic cow dairy they knew and respected lost its milk sales contract. Jennifer knew there was a need for a lactose-free product, so she began buying the cow’s milk and quickly put the extra space in their plant to use. In 2010, Green Valley Creamery lactose-free cow’s milk yogurt was launched. The brand now also produces lactose-free kefir, sour cream, cream cheese, cottage cheese, and butter. Jennifer says, “We have many lactose-tolerant customers, as the products are so tasty that if one family member needs lactose-free, the rest can enjoy them, too.” See the box for how to make lactose-free milk at home.
The company has seen much change over their five decades, including the sad loss of Steven, who passed away in 1999. In 2015, Redwood Hill Farm & Creamery, with nationwide distribution of both brands, passed the reins to the Swiss company Emmi, whose commitment to sustainability and superior management ideals Jennifer liked. She stepped down as CEO after the company’s fiftieth anniversary. However, she retains the original Redwood Hill Farm, also known as Capracopia, which is the happy home to not only about 300 dairy goats but also olives, hops, fruit trees, beehives, chickens, and vegetable gardens. Jennifer says that she has come full circle. Not only does she still live at the farm her parents founded, but so does her brother Scott (who is the farm manager) and his wife, Cristi, along with their two children and their own goats.
To learn more about Redwood Hill Farm & Creamery and Green Valley Creamery, including events and tour opportunities as well as goat’s milk and lactose-free products, visit their websites (see Resources).
Home-Produced Milk
I have so much to say about this topic that I wrote an entire book on it, The Small-Scale Dairy, but I’ll sum up a few things here. The home milk producer must learn a great deal about animal health and proper milk collection in order to produce safe, delicious milk. A lot of work goes into the process, but the resulting milk has the potential to be superior to anything you can buy in the store.
Through her milk, an animal can pass diseases (called zoonotic diseases) to humans. In addition, an animal that isn’t diseased but isn’t vigorous or being fed optimally can harbor extremely dangerous bacteria in her udder — sometimes without any symptoms.
Milk must be collected from healthy animals in an extremely clean fashion, filtered, and then chilled rapidly to prevent the growth of the microbes collected during milking. Factors such as where the animals are milked and how clean the animals are greatly influence the levels of bacteria, yeasts, and molds collected during milking.
If you want to work with raw milk and ferment without doing any heat treatment, then you must understand the importance of good hygiene! If, however, you plan on heat-treating the milk, then that step should eliminate any dangers, but remember that the cleaner the milk, the better the flavor.
Farmer-Sourced Milk
You may live in a state where it is possible to purchase milk directly from farmers. Although the sale of Grade A pasteurized milk (the kind you find in every grocery store) is highly regulated by the U.S. Food and Drug Administration (FDA), individual states can have their own regulations allowing for and regulating the sale of unpasteurized milk directly from the farm to the consumer. Typically the regulations set limitations upon the farmers, such as the number of animals they can milk or the volume of milk they can sell. Some states allow what are called herdshares, where the consumer is considered to own all or “part” of a cow, goat, or sheep and pays the farmer to take care of it in exchange for a portion of the milk. The depth and legitimacy of herdshare arrangements vary widely.
If you obtain milk by any of these means, you owe it to yourself and your family to look into the health and safety practices of the farmers. Believe me, any farmers worth buying milk from will embrace your eagerness to learn and will be glad to answer any questions you have. If they aren’t transparent with you about their process, then I highly encourage you to seek a different source — even if that is pasteurized milk from the grocery store.
Dairy Milk Deconstructed
Milk is made up of water, fat, proteins, minerals, and a few other minor components. Nature has designed milk to carry these components in the ideal proportions to nourish the appropriate infant. In fact, the composition of a mother’s milk changes throughout her lactation to meet the changing needs of the growing baby! If you keep that in mind, you’ll start to understand why milk from a single source and a small herd can be so variable. When milk is processed on the industrial scale, however, these factors are all but eliminated, due to the milk being collected from any number of farms and a multitude of animals at different stages of lactation, and the subsequent standardization of the amount of fat in the milk. In some respects, this makes working with commercially produced milk easier, as it will be more consistent, even if disappointing to some degree. Let’s take a look at the components of milk that are critical for successful fermentation and how those might vary across species, breeds, seasonality, and more.
Water
Milk is mostly water. However, even small variations in the amount of water compared to the solid components — fat, protein, lactose, and minerals — will create different thicknesses of ferments. Sheep and water buffalo are known for their more concentrated (less watery) milk. Within species, different breeds show great variation in the water content of their milk. For example, a big Holstein cow has more diluted milk than a small Jersey cow. Likewise, in goats, the largest dairy breed in the United States, the Saanen, has more water and fewer solids in its milk than the smallest breed, the Nigerian Dwarf. Knowing this information can help you tweak recipes to get the best results possible.
Lactose
This is a complex subject and, quite literally, a complex sugar. Lactose is the conjoined molecule of the sugars glucose and galactose. You’ve no doubt heard of glucose, but galactose spends less time in the spotlight, and indeed, it plays a slightly lesser role in milk fermentation. Many adults cannot process lactose — as we learned earlier, their bodies lack the ability to produce lactase, the enzyme that splits lactose into its two simple sugars so that the body can use it. However, the lactic acid bacteria (LAB) that ferment milk also produce the lactase enzyme by which they first split the lactose molecule into glucose and galactose, and then through an extensive pathway of breakdown, produce lactic acid (and in some cases also ethanol alcohol and carbon dioxide gas). The longer the milk ferments, the more lactose the bacteria break down, although there is usually some residual lactose as well as glucose and galactose at the end of the process. For this reason, even people who are moderately lactose intolerant can often digest fermented milk products.
In general, the lactose content of milk decreases toward the end of the animal’s lactation, when her baby doesn’t need milk as its primary energy source anymore. If you are making yogurt and kefir with milk from your own animals, you might notice that as the animal nears the end of its lactation, the yogurt or kefir takes a bit longer to thicken and get to the desired tartness. This is most often because the LAB have less lactose to consume and so don’t produce the same amount of lactic acid as quickly. They may eventually do so, but it just takes longer. (There are other, less likely factors that can also slow fermentation.)
Koumiss is a traditional milk ferment made with mare’s milk, which has a much higher lactose content (over 6 percent) than cow’s, goat’s, or sheep’s milk. The additional sugar in mare’s milk allows for a greater degree of fermentation, transforming the milk into a beerlike fermented beverage. We’ll make a mock koumiss in chapter 6.
Protein
The protein in milk can be divided into two primary categories: caseins (sometimes called cheese proteins, as they are the building blocks of the structure of cheese) and whey proteins (normally lost in the liquid whey during cheesemaking). The total protein content typically ranges from 3 to 4.5 percent, and it is usually a bit lower than the fat percentage of the same milk. On average, cow’s milk proteins exist in a ratio of 80 percent caseins to 20 percent whey proteins, while goats have a 70:30 ratio.
There are several types of proteins within the casein group, some of which are the best for making cheese. Cheesemakers add rennet, which causes milk proteins to knit together, or coagulate, forming a gel-like curd, and some casein types are basically better at forming this gel. Yogurt and kefir, however, don’t rely upon rennet for their formation. Instead, the acid produced by the fermentation bacteria thickens the milk by causing the milk proteins to stick together rather than repel each other. (An exception is the Icelandic yogurt called skyr, which uses a touch of rennet; see the recipe.) For this reason, the types of casein proteins in the milk aren’t as important to the yogurt and kefir maker as they are to the cheesemaker. However, the total amount of caseins does matter. If you take a look at the chart, you’ll see that the total protein content varies quite a bit between species. The more protein a milk has, the thicker the ferment, and, of course, the resulting product is also a better protein source for us.
Fat
Milk fat, also called butterfat, varies tremendously by species, breed, stage of lactation, and the animal’s diet (interestingly, not from eating fats but from eating the right kind of fiber). Milk fat contributes not only nutritious calories but also pleasing mouthfeel. Fat-soluble vitamins, such as A and D, are contained within the fat globule. The milk fat itself doesn’t coagulate but is suspended within the clumped milk proteins. The higher the fat content, in fact, the less firm the curd.
Minerals
Minerals such as calcium don’t play the major role in creating yogurt and yogurt-like ferments that they do in the more complex fermenting processes entailed in cheesemaking, where they help rennet coagulate the proteins. But their presence is one of the reasons for the high level of nutrition provided by real dairy ferments. In general, the higher the protein content, particularly the caseins, the higher the mineral content of the milk.
Average Milk Components by Dairy Species
Animal
Lactose
Fat
Total Protein
Cow
4.8%
3.7%
3.4%
Goat
4.1%
4.5%
2.9%
Sheep
4.8%
7.4%
4.5%
Water buffalo
4.5%
6.0%
4.5%
Sources: P. F. Fox, T. P. Guinee, T. M. Cogan, and P. L. H. McSweeney, Fundamentals of Cheese Science (Aspen Publications, Inc., 2000), and R. K. Robinson and R. L. Wilbey, Cheesemaking Practice (Kluwer Academic/Plenum Publishers, 1998)
Plant Milks
Plant milks offer alternatives to those with dairy allergies, lactose intolerance, or unanswered concerns about animal welfare. However, plant milks can be challenging to ferment and will create flavor profiles that are quite different than those of their dairy counterparts. If you are trying to create a truly vegan product, you’ll have to make sure that the microbial cultures you use are labeled “nondairy” or “dairy-free.” I’ve listed some options in chapter 7.
Plant milks don’t contain lactose, which is the primary food for yogurt and kefir fermentation bacteria. They also lack milk proteins (caseins), which naturally thicken dairy fermentations. For these reasons, plant milk ferments often include added sugar and thickeners. Remember, the bacteria require sugar in order to ferment, and they will make do with a source that provides glucose (such as table sugar and honey). And added thickener isn’t necessarily bad for you. In fact, many thickeners contribute slight nutritional value or another health benefit. See instructions on making your own plant milks.
Soy milk is made by soaking dried soybeans and then grinding and straining the mixture to extract the liquid. When made from sprouted soybeans, fresh soy milk can be delicious and quite healthy, as sprouting unlocks some of the otherwise indigestible aspects of fresh soy. Unfortunately, most commercial soy milks are not made from sprouted soybeans. The sugars naturally present in soy milk provide some food for the lactic acid bacteria — usually enough that they can ferment it to close to the same acid level as dairy yogurt. Fresh, homemade soy milk is the best choice, but some fresh, chilled grocery-store versions can work, as long you avoid the shelf-stable variety, which has a lot of additives.
Almond milk is created along the same lines as soy milk. Almonds are soaked and then ground, and the resulting slurry is filtered to remove the liquid. Sugar and thickeners must be added to almond milk in order to convert it to kefir or yogurt. Fresh, homemade almond milk is the best choice, but some fresh, chilled grocery-store versions can work. As with soy milk, avoid the shelf-stable variety.
Coconut milk is made from the white flesh of the fruit, which is ground, mixed with hot water, pulverized, and then filtered. Depending on how much water is added, you end up with various versions of coconut milk, from light to cream. Thickeners are needed in varying amounts, depending on the density of the coconut milk, in order to create the familiar thickness of yogurt. Other than fresh, I choose canned coconut milk and cream meant for cooking. It’s the least adulterated and the thickest. Coconut milk makes the most flavorful vegan ferment, in my opinion, but I love the flavor of coconut!
There are other plant milks on the market today, including hemp, macadamia, cashew, and rice milks. Most are sold as beverages and include many other ingredients, including thickeners and flavorings. All can be used to make plant milk ferments, but as with other plant milks, you will likely need to add sugar and thickeners.
Microbial Cultures
Microbes — bacteria, yeasts, and molds — are responsible for fermentation. In the case of milk fermentation, it’s usually bacteria and sometimes also yeasts. Collectively, these microbes are called culture. As we learned in chapter 1, the microbes that are naturally present in the environment enter the milk at any number of points as and after the milk leaves the animal’s udder. (Note: You are unlikely to get a good ferment from wild microbes in plant milks, due to the processing steps of creating the plant milk.) As milk fermenters, we usually have no way of knowing whether these “wild” microbes will help us ferment the milk in a pleasant way or contribute to spoilage — or in the worst case, make someone sick. For that reason, in almost all cases we must add a reliable source of microbes to the milk (although there are still some wild milk ferments happening around the world, and they have some interesting sources for microbes, including even banana leaves). The cultures that we add come powdered (freeze-dried) or fresh (a bit of ferment from a previous batch). Some cultures are heirlooms, having been passed down for generations. We also have what are called kefir grains — clumps of microbial communities used especially for making kefir.
Powdered Cultures
Powdered cultures are produced by a fairly limited number of manufacturers, most of which are located in Europe. These cultures are grown and standardized to ensure that they will produce the right amount of acid, then they are tested for pathogens, freeze-dried, packaged, and given a lot number and expiration date. This makes them the ideal choice for larger producers who must meet stringent food safety requirements. They are also quite convenient for home producers, as you can keep them in your freezer and use them as you need. In the resources section as well as near the recipes, you’ll find listed just a few of the many suppliers of these powdered cultures.
Powdered cultures are sold in packets (sometimes called sachets) or plastic vials. The culture is freeze-dried, so it will last a long time if stored properly. Keep the packets in the freezer, and do your best to protect them from humidity, as moisture will activate the microbes and then they will perish if not used right away. The best way to keep moisture out is to either use the contents of a packet all at once or reseal and return to the freezer. To protect cultures that come in a vial, open the vial in a dry area (in other words, not right over a steaming pot of milk), and then re-cap and return to the freezer. Also, don’t dip your measuring spoon into packets or vials; instead, dispense the powder out of the container into your measuring spoon. This helps prevent moisture and other contaminants from getting in.
Fresh Cultures
You can start all batches of yogurt and cultured kefir with a bit of store-bought product or your previous batch. There’s a catch, though — for the best results, the fresh culture source must truly be fresh! As a milk ferment sits, even for a few days, its microbial population diminishes and its microbial variety changes. You might still get decent results using a bit of a less-than-fresh ferment as your culture, but the ferment you make probably won’t taste like the batch you took the contribution from. In addition, when you continually reculture from a previous batch, you will likely see a slow but steady decline in the success of that culture (unless it is an heirloom variety). But you won’t know unless you try! As long as your ferment thickens and sours in the right amount of time according to the recipe, your concerns won’t be about food safety — just aesthetics.
You can also freeze fresh culture. For example, if you make a nice batch of yogurt and want to use some to start your next batch but you don’t want to do it soon, freeze it right away. Store it in the coldest spot in your freezer (any partial thawing and then refreezing will damage the hibernating microbes). See instructions on how to freeze cultures.
Heirloom Cultures
Heirloom cultures are the sourdoughs of the milk fermentation universe. They are passed down through generations and around to family and friends. In Scandinavia, the dollop of ferment with which a new batch of ferment is started is often called a seed or root. (In the industry, this method is sometimes called slop back, which doesn’t sound nearly as appealing!) Heirloom ferments can’t be precisely duplicated by freeze-dried cultures, dehydrated cultures, or lab-grown versions. Their exact composition varies depending on many conditions. For all of these reasons, they are known in the industry as undefined cultures.
Unlike modern yogurt cultures, heirloom varieties can regenerate for generation after generation. If you can get your hands on a seed of fresh viili, piimä, filmjölk, matsoni, or one of the other heirloom ferments from the Old World, cherish, nurture, and, above all, share it!
Kefir Grains
Kefir grains are gelatinous clusters created and populated by communities of bacteria, yeasts, and sometimes molds. They are living sources of fermentation microbes. There are two main varieties: milk kefir grains (referred to in this book as simply kefir grains) and water kefir grains. Either can be purchased fresh, dried, or frozen. Milk kefir grains contain microbes that ferment milk sugar, while water kefir grains ferment sucrose (table sugar).
Like sourdough starter, kefir grains must be fed very regularly or their diversity will shift and/ or they will die off. Maintaining fresh or reactivated (from dried or frozen) grains is a bit of a commitment — about the level of caring for a goldfish, but with greater rewards. Read more about caring for grains.
A single large kefir grain cluster
Microbial Diversity
A wide range of wonderful microbes grows well in milk. Some of them are good at converting milk sugar into acid and other by-products, others are good at providing nutrients and support for other milk microbes, and others are best at providing aesthetic nuances and/or probiotics. In milk ferments, they work in collaboration throughout the fermentation. The chart lists a range of fermentation bacteria and their main contributions to the process. I don’t list yeasts here, but when present they all have a similar function: the production of carbon dioxide and flavor.
You’ll note in the chart that each bacterial species has a range of temperatures in which it will grow best. When the temperature is below that range, the bacteria won’t die, but they will stop reproducing and fermenting. Above that range, they will stagnate or die. This is why tiny differences in fermentation temperatures can create big differences in the end product.
Commercial culture manufacturers work hard to create blends of different microbes, including proprietary strains whose designation you likely will never see on the label. Commercial yogurt and kefir makers also work with companies to customize their culture blends to offer something unique to the consumer. At the beginning of the yogurt and kefir recipe chapters, I list some blends I’ve tried and their sources.
If you are working with an heirloom starter, you are working with a changing population of microbes. Indeed, when an heirloom is passed down, each generation of microbes is likely to change ever so slightly. A healthy heirloom that is well tended should continue to function well, even with population changes over time.
Common Milk Fermentation Bacteria
Bacteria
Growth Temperature Range
Primary Function
Primary Milk Ferment Applications
Bifidobacterium bifidum, B. breve, B. infantis, B. longum, B. spp.
Mesophile; 72°F–118°F (22°C–48°C); ideal at 97°F (36°C)
Probiotics, acid, and flavor
All
Lactobacillus acidophilus
Thermophile; 81°F–118°F (27°C–48°C); ideal at 97°F (36°C)
Probiotics and some acid
All
Lactobacillus casei
Mesophile; 59°F–105°F (15°C–41°C); ideal at 99°F (37°C)
Acid and probiotics
Kefir and kin
Lactobacillus delbrueckii ssp. bulgaricus
Thermophile; 73°F–125°F (23°C–52°C); ideal at 113°F (45°C)
Acid and flavor
Yogurt and kin
Lactobacillus delbrueckii ssp. lactis
Thermophile; 65°F–122°F (18°C–50°C); ideal at 104°F (40°C)
Acid and flavor
Matsoni and kefir
Lactobacillus helveticus
Thermophile; 72°F–129°F (22°C–54°C); ideal at 108°F (42°C)
Acid and flavor
Kefir, koumiss, and other old-world ferments such as matsoni
Lactobacillus kefiri
Mesophile; 46°F–109°F (8°C–43°C); ideal at 89°F (32°)
Acid
Kefir
Lactococcus lactis ssp. cremoris
Mesophile; 46°F–104°F (8°C–40°C); ideal at 72°F (22°C)
Acid and texture (some strains produce exopolysaccharides)
Buttermilk, cultured butter, sour cream, kefir, viili, and others
Lactococcus lactis ssp. lactis
Mesophile; 46°F–104°F (8°C–40°C); ideal at 86°F (30°C)
Acid
Buttermilk, cultured butter, sour cream, and kefir
