Cereal Mashing or How I plan to make the best oatmeal stout ever:

HBS Blogger Chris Corcoran

The holidays are over, the sun is staying out a little longer each day, and it’s still bitterly cold out…..must be January! I haven’t put out a post in a while but that doesn’t mean I haven’t been brewing. Currently the Eisbock is cold conditioning and I’ll be freeze distilling it in just a few weeks. First, my buddy and I are going to practice freeze distilling on his Apple Wine. I’ll have the full write up in about a month.

The other day I was asked about substituting Stone ground oats in place of the brew store’s standard flaked oats. My answer? Cereal mash! The idea is simple; much of what we eat has some sort of starch and these starches are converted into sugar in the mashing process. So how exactly do you use store bought old fashioned stone ground oats or any other starch laden food (potatoes, wheat, rice, corn, etc.) in brewing?

When you buy flaked oats in the brew store the oats have already been gelatinized, rolled, and made ready to use. We simply have to do this ourselves and it is no more complicated than making a bowl of old fashioned oatmeal.

The process is called a Cereal Mash. The process is very simple.

1: Break down your adjunct in to small pieces. Mill, ground down, cut, or shred the adjunct into a fine grist, no bigger than oatmeal, no smaller than your milled grain. Try to keep this adjunct between 10 and 20 percent of your total grain bill. The enzymes in your grain will be what breaks down the starch. Too much adjunct and you won’t convert all the starch, too little and you won’t get much noticeable contribution.

2: Add warm water to the milled adjunct. I shoot for water at about 150 degrees. Most starches will gelatinize at around 150 degrees, some starches benefit from a slightly lower temp (oats and wheat) while some like higher temps (rice and corn). I add about 2 quarts of water per pound of adjunct. Let rest at this temp for 15 to 20 minutes.

3: After the rest, bring the mash up to a boil for 20 or so minutes. Keep stirring so that the contents don’t burn! If the boil is too thick add a little extra water.

4: Lastly, add your adjunct to your mash. There are several different ways to do this step and much will depend on your set up and experience. The first option is to treat the cereal mash as a decoction mash or step mash addition. Aim to have your initial mash at protein rest levels (120 degrees to 130 degrees) and then add the boiling water/adjunct mix in to raise your temp up to saccrification rest. Another option is to cool your cereal mash down to your saccrification rest temp before adding it in. Any way you go, you’ll need to do some on the fly adjustments. I’d recommend having some extra hot and cold water around to help adjust your overall mash temp.

I’m brewing up my Oatmeal stout this weekend and will be using 1.5 lbs. stone ground oats in place of the standard 1 lb. flaked oats. I hope to achieve a pleasantly strong oatmeal flavor. I’ll let you know how it goes!