Q&A with THE BEER DOCTOR – Home Brewing Edition

by Dr. Carol Westbrook on August 14, 2011

Q Do you know anything about this process? I read; cereal containing certain sugars will undergo something called, spontaneous fermentation that is caused by wild yeasts floating in the air, if stored in certain kinds of containers for a long period of time , it will produce a beer-like drink. Next question: Are they referring to cereal like we eat today or is it a ingredient used to make beer ? 

A. You’re missing one thing — water. The addition of yeast and water to sugar will produce alcohol and carbon dioxide (carbonation) if oxygen is kept out, but in the presence of oxygen it will turn into vinegar. This is known as fermentation. As you surmised, the term “cereal” does not mean corn flakes, but rather refers to cereal grains, such as barley, wheat, corn, or even millet. Although cereal grain does not contain much sugar, if you wet it and let it sprout, the starch will be broken down into sugars by the enzymes in the sprout. This is called “malting” the grain. Add yeast and voila, you have beer! That is, providing you keep it tightly covered, though you’ll have to lift the cork occasionally to release the gas pressure. There is plenty of wild yeast in the air, so it’s likely that this will happen spontaneously if your grain stockpile gets wet and is stored in a covered jar. No doubt that is how beer was discovered initially. You can try this at home, though you might find it easier to use apple cider than fresh grain. (You can buy grains online at a brew supply store, if you are interested). And speaking of those wild yeasts, they are quite unpredictable in flavor and characteristics, so most brewers today use pure yeast strains. But some beers are still produced with wild yeast and have a distinctive taste, such as the Belgian Saison or farmhouse-style ale.

Q. Wow, thank you. I was so confused , I thought they were speaking of cereal like we eat for breakfast. This is very interesting stuff. OK, on more question wild yeast in the air. Before I read the article I had never heard of wild yeast in the air, If I did it was one of those things I learned in college that i never gave any thoughts. I am a Chef so am familiar with activating yeast but would love to learn more about beer making and the wild yeast

A. Yeast is an amazing creature! There are thousands of strains of yeast and they are all different! Yeasts produce bread, beer, ripened blue cheese, beer, wine, penicillin; some cause disease; others are used in science experiments. All yeasts can ferment sugar to alcohol, but wild yeast is an unpredictable mixture. Beer made with wild yeast can taste sour and pungent, like sourdough bread. Unless you are trying for this taste, it’s best to buy purified strains, whether you’re making beer, cheese, or bread.

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