Most people know that Yeast is one of the 4 key ingredients in a beer (along with water, hops & malted barley), but do you know exactly what that yeast is doing? Unless you’re an avid brewer yourself, and you’ve done your homework (or were lucky enough to get to write a report on the topic for your college chemistry class a few years ago), you probably don’t know too much about the actual chemistry involved in making those four, seemingly unrelated ingredients into that wonderful fermented concoction we all love so dearly. Well, here is the play-by-play on the natural science of brewing. While reading, you might crack open your favorite brew, to further appreciate the marvelous result of the process of science (and hell, it just makes it more fun).
1. Malting: “Malting” is the controlled germination of barley (say what?). After steeping the barley in water, the grain is spread on a malting floor and allowed to grow until it is modified. Natural enzymes transform the endosperm from complex to simple starches. The grain is dried at high temperatures and milled.
2. Mashing: Bringing the “mash” of grains to between 148 and 158 degrees activates a pair of related enzymes that liquefy and reduce the now-soluble starches into maltose and other simple sugars.
3. Lautering: Once all reducible starches have been converted, the mash is heated again to 170 degrees. The liquid is usually drained out through a bed of the original grain; the husks are then rinsed (“lautered”) thoroughly with more hot water. The collective runoff from the mash is called “wort,” and it constitutes what will become the finished beer.
4. The boil: Achieving clear beer with a firm, foamy head is largely a function of removing most – but not quite all – proteins from the original mash. Proteins, when boiled, will coagulate and settle out of the liquid (forming a gummy mass called “trub”); this action is called the “hot break.” Boiling is also necessary to extract important flavoring agents, called alpha acids, from hops. For the most part, the longer the wort is boiled, the more efficiently a given amount of hops can bitter a quantity of beer. Boiling even longer can produce caramelization of sugars in the wort.
5. The cold break: As soon as the boil is complete, the wort is quickly cooled; this removes even more undesirable proteins and tannins out of the wort. This time the process is called the “cold break,” and the residue is called “cold trub.”
6. Pitching the yeast: Perhaps the most important key to making good beer is to keep wild yeast and bacteria from gaining a foothold in your brew before the preferred yeast does. This is done through good sanitation and proper “pitching” of a sufficient quantity of carefully cultivated beer yeast. When the wort is cooled, a thick broth of cultivated yeast is added.
- A. The lag phase: The yeast immediately begins to absorb oxygen. Enzymes facilitate yeast’s intake of glucose, more complex sugars and other nutrients. This happens in a few hours.
- B. The respiration and fermentation phases: With sufficient food reserves stored away, the yeast begins to reproduce by “budding.” It absorbs all the remaining oxygen in the wort and uses it and other nutrients to produce new “daughter” cells. Once all oxygen is absorbed, reproduction halts and fermentation proper begins. In a simplified explanation, yeast turns one molecule of glucose into two molecules each of ethyl alcohol and carbon dioxide.
- C. Clarifying and carbonation: Once all available fermentable sugars are consumed, fermentation grinds to a halt and the yeast begins to go dormant. The beer is clarified by storing in a cool, still, sterile environment. It is now nearly free of clouding agents and is clear. It is also flat. During the whole fermentation process, the huge amount of carbon dioxide produced has been allowed to escape through a gas vent, while the alcohol has been preserved in an otherwise closed environment. To achieve carbonation, brewers inject carbon dioxide to the desired level.
So, next time you sit down with a glass of your favorie beer, think about all the hard work the yeast enzymes did to produce your brew and toast one to them; you couldn’t have done it without them!
[special thanks to an article by Jim Price of The Telescope for supplying the information]