APPENDIX B

The Infusion Mash

Infusion mashing follows different principles for extracting malt than decoction or step mashing. Infusion mashes have only one temperature rest; they do not include a protein rest. Only well-modified malts can be infusion mashed. Mashing and sparging generally take place in a dual-purpose tun over a two- to three-hour period.

The classic infusion mash is not stirred. It entrains and retains a great deal of air; consequently, it “floats.”

The greatest challenge in an infusion mash is to achieve and maintain a reasonably even saccharification temperature. Unless the mash can be raked during sparging, an infusion mash can’t be stirred to disperse temperature evenly, because stirring deaerates the mash, and the lauter mash will set. Entrained air keeps an infusion mash from settling until late in the sparging cycle.

Temperature variation within the mash, then, is almost inevitable, and within limits is considered acceptable. So long as variations do not exceed ±2 degrees F (1 degree C) of the target saccharification temperature, attenuation consistency will be acceptable.

A mash program should not be chosen to suit the style of beer being brewed, with the single exception that a decoction mash is specific to developing the maltiness that is characteristic of some lager beer styles (Munichs, fests, alts). All ales and most lagers can be made from infusion, decoction, or step mashes.

The choice of a mash program is determined by the character of the malt being used. The infusion mash is designed for use with well-modified malt that can be extracted by a single rest in the 149 to 158 degree F (65 to 70 degrees C) range. English pale and mild malts are not the only malts that are suitable for infusion mashing. Most modern malts, including those of continental origin, can be infusion mashed. The criteria for whether or not a malt can be infusion mashed are: a fine/coarse extract difference of less than 1.8 percent, a soluble nitrogen ratio (S/T) of at least 38 percent, and malt that is at least 95 percent mealy. Where no lot analysis is available, acrospire growth examination should give at least 90 percent grown to two-thirds the length of the kernel, and the majority at three-quarters-to-full-kernel length. Beers that will be served very cold may show a protein haze if malt of more than 1.6 percent nitrogen (10 percent protein) with a soluble nitrogen ratio less than 40 percent is mashed without a protein rest.

Traditional Infusion Mash

If the malt is well converted and perfectly crushed, if the saccharification temperature is reasonably uniform, if the mash floats well, if sparging is evenly dispersed, if the lauter mash is raked and the sweet-wort runoff is restricted so that it takes ninety minutes or so to collect, an infusion mash will give nearly the same extract as a step or decoction mash would. In practice, however, infusion mashes give 3 to 10 percent lower extract, depending upon the particular brew house’s efficiency.

The saccharification temperature for an infusion mash almost always falls between 149 degrees F (65 degrees C) and 158 degrees F (70 degrees C). And 149 degrees F is the temperature at which malt starch gelatinizes, so the saccharification temperature should be at least 149 degrees F for malt starch to be made easily accessible to diastatic enzymes. Beta-amylase is still very active at 149 degrees F, while alpha-amylase is somewhat subdued, so the maltose-to-dextrins ratio of the wort will be very high, and the wort from a 149 degree F mash will be composed primarily of fermentable sugars. A final gravity (apparent) of 20 to 25 percent of the OG usually results. At 158 degrees F, beta-amylase is almost entirely deactivated, while alpha-amylase is performing at its peak. The greater percentage of maltotriose, maltotetraose, and dextrins in a wort from a 158 degree F mash will give a beer with a high end-gravity (33 to 35 percent of the OG). Mashes within the range bracketed by these temperatures give intermediate results; at 153 to 155 degrees F (67 to 68 degrees C), the FG might be expected to be 28 to 32 percent of the OG.

The duration of the saccharification rest also affects fermentability and flavor. A 120-minute mash is going to eke out every bit of diastatic power that the malt has to offer, while a 45-minute mash at the same temperature is going to leave more large polysaccharides. Consequently, a two-hour mash at 149 degrees F is going to give a beer with a lower final gravity than a 45-minute mash at the same temperature.

Finally, mash thickness will affect fermentability. The thicker the mash, the more effective the enzymes will be, and the longer their power will last. Alpha-amylase is especially sensitive to mash thickness. When brewing for a dextrinous wort, it is important that the mash be kept thick, so that alpha-amylase will not be degraded before all the malt starch is reduced to at least dextrins. The greater the degree of attenuation desired, the thinner the mash should be. It is common to gradually thin an infusion mash with boiling liquor when it is for a well-attenuated beer.

The quality and uniformity of crushing is more important for an infusion mash than for a multitemperature program. The crush needs to be relatively coarse, so the mash will float, but not so coarse that all the kernels aren’t at least fully cracked, or the starch won’t all hydrolyze. On the other hand, predominantly shredded husks and a high percentage of flour almost ensure a stuck mash.

Historically, the extract of infusion mashes was run off completely after conversion, and the mash was reflooded with hotter liquor and run off a second time in lieu of sparging (double mash). In modern practice, sparging is carried out as for step and decoction mashing, except that the liquid level above the settling grain is not usually lowered as rapidly. Sparging may begin almost immediately after the runoff is begun, and the liquid level may be lowered only gradually.

Since there is little remedy for temperature, thickness, or pH shortcomings in a mash that can only be stirred moderately, the mashing-in for an infusion mash needs to be competently handled. The malt is usually mashed-in with liquor at a strike temperature that is 10 to 20 degrees F (6 to 11 degrees C) hotter than the target mash temperature, depending on the temperature of the malt itself, the ambient temperature, the temperature and insulating properties of the mash-tun, and the mash thickness desired. With a poorly insulated tun, the mash needs to be made up thick, so that subsequent temperature-maintaining liquor infusions won’t dilute it so much that the liquid weight forces the grains to sink. In general, where the crushed malt, whether dry or hydrated, drops into liquor/mash in the tun, the mash floats better than if the liquor is added to dry malt in the tun.

The alkalinity of the liquor is critical to the mash pH. When mashing pale malts, the liquor pH needs to be adjusted to below 6.8 for soft waters and as low as 5.8 for hard waters to realize a pH of 5.2 to 5.3 in the mash. As the percentage of dark malts increases in a mash, it becomes less sensitive to the pH of the liquor.

Where very dark or crystallized malts are called for in a recipe, many brewers wait until the end of the mash to add these malts so that exposure to the hot liquid does not unnecessarily extract tannins from the husks. Since these malts do not contain raw starch, they do not need to be saccharified.

Infusion Mash Procedure

Crush the malts. Infuse with 1 ¼ to 1 ½ quarts of liquor at 160 to 180 degrees F (71 to 82 degrees C) per pound of malt for a saccharification rest at 149 to 158 degrees F (65 to 70 degrees C) and mix gently. Check and record the pH and temperature of the mash. Maintain the rest temperature for forty-five to sixty minutes, or for up to a maximum of two hours for greater attenuation. Make boiling-liquor infusions as necessary to maintain the mash temperature. Crush and hydrate roasted and crystal malts as the end of the mash nears. Confirm the degree of saccharification by iodine testing; for a dextrinous wort, the mash can be concluded once the iodine reaction falls off to a mahogany color.

Begin to run off the sweet wort slowly. Begin sparging with liquor at 170 to 175 degrees F (77 to 80 degrees C) when the grist begins to sink. As the mash level drops, let the liquid level drop proportionally; not more than two inches of liquid should stand above the grains during sparging.

Terminate the runoff when the pH of the sweet wort rises above 5.8 or the density drops to 3 °Plato (SG 1012).