One of the advantages of all-grain brewing is the ability to use ingredients that can't be used in extract brewing. Specifically, all-grain brewing allows brewers to use starchy grains or adjuncts that would cause haze (and instability) in an extract beer. Because grain-derived enzymes in the
mash (alpha and beta amylase) degrade starch into simple sugars, starchy adjuncts can be added to an all-grain mash.
In order to degrade starch in a mash, however, the starch needs to be accessible to the starch-degrading amylase enzymes. In most plants, including barley, starch is stored in granules. In these granules, starch has an organized structure. When a starchy food is soaked in cold or luke-warm water, the starch absorbs some of the water, but the granules remain essentially intact. Within a range of temperatures, however, the starch loses its structure and becomes a "net" of starch with lots of water molecules interspersed. This is called the gelation range. Above the gelation range, the starch dissolves into the water. Because the starch-degrading amylase enzymes are water soluble, they can then get to the starch and begin degrading it.
(A note: starch gelation is often referred to as starch gelatinization. Technically, gelatinization is the process that occurs to gelatin (a protein) in hot liquids. Gelation is the proper term for the process in carbohydrate gels.)
The gelation range varies among starches for different types of plants. Most, however, begin the range of 120–140 °F (50–60 °C). [Differences exist among plants starches because different plants have a different ratio of amylose (straight-chained starch) to amylopectin (branched starch).] An upshot of this is that many grains or other starchy adjuncts can simply be stirred into the mash. The temperatures in the saccharrification range are sufficient to gelate the starch and render it accessible to amylase enzymes. Unmalted barley and unmalted wheat, for example, are two grains that can be mashed. Some starches, however, have gelation temperatures starting above mash temperatures. Likewise, some starchy adjuncts have traditionally been boiled to obtain a better extract or to speed up hydration.
Corn grits and rice are two common adjuncts in American Pilseners (and American Bocks). These ingredients are boiled, along with a small amount of barley malt, in what is called a cereal mash. Also, in traditional Belgian lambic brewing, raw wheat is sometimes boiled — again, with a bit of malted barley — before stirring it into the mash. (A step mash is used in other occasions.) This is not called a cereal mash, but the process is the same. For brevity, I'll simply call the process "a cereal mash" rather than "a cereal mash or the process that's exactly the same as a cereal mash but not labeled as such because a standard beer grain or non-cereal adjunct is involved."
Learning to perform a cereal mash not only allows you to brew American Pilseners (including classic American Pilseners), American Bocks and lambics, it also allows you to experiment with many types of grain or other starchy foods that are not malted. Beers brewed with potatoes, sweet potatoes and tapioca, for example, can be made if you know how to do a "cereal mash."
What you'll need
The only equipment you'll need for a homebrew cereal mash is a pot and a spoon. I brew outside, using two "turkey fryer" set-ups — one for my hot liquor tank and another for the brewpot. When I do a cereal mash, I simply use my old 5-gallon (19 L) brewpot on my kitchen stove.
In an American Pilsner, 30-40% of the grain bill is rice or corn. The rest is 6-row pale malt. This gives a good upper limit to the amount of adjunct you would want to use. (Use the dry weight of the ingredient when calculating this.) For 2-row malt, which has fewer enzymes, an upper bound of 30% would be prudent. If you have worries about converting all the starch in your recipe, perform an iodine test and do not mash out until it tests negative. (You can also add commercial preparations of amylase enzymes.)
When you plan to utilize a grain or starchy adjunct using a cereal mash, you will need to plan whether you want to do a step mash or a single infusion mash.
A traditional cereal mash, of the type used in making American Pilseners, is part of a step mash program. In this mash program, the barley is mashed in at a temperature below the starch conversion range. The cereal mash — which is about 30–40% the size of the main mash — is boiled, then pumped into the main mash. The heat from the cereal mash raises the temperature of the main mash. See the recipe for an example of a stepped cereal mash. As a homebrewer, however, you can also opt for a single infusion mash along with your cereal mash. To do this, boil your cereal mash but do not mash in the rest of your grains initially. When the cereal mash is ready, combine it with the crushed grains and hot water to mash in at your preferred temperature.
A single infusion mash is conceptually simple, but it can be difficult to hit your mash-in temperature. I've done this a few times with my sweet potato ales and have found an easy way to hit the right temperature. For a "single cereal mash," heat your brewing liquor to about 11 °F (6 °C) over your target mash temperature as you usually would. But, keep some room temperature water on hand. Stir the cereal mash into your dry grains, then quickly start adding water to your mash. (Stir vigorously since you're stirring water into the grain.) When your mash is a very thick, oatmeal-like consistency, take the temperature. You should be close. Bring the mash up to your normal consistency by adding small amounts of room temperature water, hot brewing liquor or mixtures of the two, as needed. Work steadily, but don't sweat if it takes you a few minutes to go from thick mash to the proper consistency.
How to cereal mash
To do a cereal mash, combine your "cereal" — whether, it's corn or rice, an unmalted grain or other starchy food — with about 10% six-row barley malt or 15% two-row barley malt. The malt should be crushed and — if your cereal is another grain — crush that too. Slice, dice or otherwise reduce the size of other starchy foods to small enough pieces so that they will hydrate quickly. You can go higher on the barley percentage if you want, up to around 30% if you wish.
Add water and begin heating the cereal mash. Shoot for a thin gruel-like consistency. Some foods will take on water as they cook, so don't be afraid to add water as you go if the cereal mash gets too gooey.
Bring the cereal mash to the high end of the starch conversion range, around 158 °F (70 °C) and hold for 5 minutes. The barley malt in the mix will convert any stray starches at this point, but the bulk of the starches will be converted in the main mash. (Even with starchy foods with a low gelation range, there is not enough enzymatic power in the cereal mash to fully convert it.)
After the five-minute rest, bring the cereal mash to a boil. You will need to stir nearly constantly as it heats and boils to prevent scorching. Boil the mash for 30 minutes. When the cereal mash is done, stir it into your main mash. At this point, the starches in the cereal mash will be exposed to the amylase enzymes in the main mash and degraded. At this point, you simply finish brewing as you normally would.
Grains and astringency
At this point, some all-grain brewers may be wondering about astringency. If you boil an unmalted grain, won't you extract tannins from the grain and get a horribly astringent beer? After all, when sparging, you are told not to exceed 170 °F (77 °C).
In fact, the pH of the boiled mash will be fairly low and not conducive to tannin extraction. This is why decoction mashes don't yield terribly astringent beers (although a small amount of astringency can develop in a decoction mash). In a grain bed rinsed with sparge water, the pH is much higher and the temperature must be kept lower. If you use large amounts of a husky grain, astringency is a possibility. However, it is not assured.
Why should I try it?
Learning to do a cereal mash adds another tool in your bag of brewing tricks and allows you to experiment with new ingredients not found at your local homebrew store.
The Cream Police
(5 gallons/19 L, all-grain)
OG = 1.045 FG = 1.009
IBU = 17 SRM = 4 ABV = 4.7%
For the "corniest" cream ale you can make, a cereal mash with corn grits is just the thing. This recipe will show you that cereal mashing is a useful homebrewing technique and not just a Cheap Trick.
8.0 lbs. (3.6 kg) 6-row pale malt
1.8 lbs. (0.82 kg) yellow corn grits
4.66 AAU Brewers Gold hops (60 minutes) (0.58 oz./17 g of 8% alpha acids)
1 tsp. Irish moss
1/4 tsp yeast nutrients
Wyeast 1056 (Amercian Ale) or White Labs WLP001 (California Ale) yeast (1.5 qt./1.5 L starter)
1 cup corn sugar (for priming)
Step by Step
In your kettle, heat 2.5 gallons (9.5 L) of water to 144 °F (62 °C). Mash in crushed 6-row malt and hold at 133 °F (56 °C). Reserve a handful of 6-row malt. In a stock pot, mix the grits and the handful of malt with water and heat to 158 °F (70 °C). Hold for 5 minutes, then bring cereal mash to a boil, stirring constantly. Boil cereal mash for 30 minutes, then add to main mash. Apply heat to bring full mash temperature to 150 °F (66 °C) and hold for 45 minutes. Scoop mash into your lauter tun and add boiling water to raise temperature to 158 °F (70 °C). Recirculate wort for about 20 minutes, then begin running off wort. Sparge with 190 °F (88 °C) water, but do not allow grain bed to exceed 170 °F (77 °C). Collect about 5 gallons (19 L) of wort, add 1.5 gallons (5.8 L) of water and boil for 90 minutes. Add hops with 60 minutes left in the boil and Irish moss and yeast nutrients with 15 minutes left. Cool quickly and transfer to fermenter. Aerate well and pitch yeast. Ferment at 67 °F (19 °C) for one week. Transfer to secondary and, if possible, cool beer to 40 °F (4.4 °C) and hold for two weeks. Keg or bottle with corn sugar.
Chris Colby writes the Techniques column in each issue of BYO.