A bit of brewing chemistry

Well, I'd be remiss as a food geek not to make a post about food science, so in response to an open invite to the Tangled Bank, I'll talk a little about beer, corn syrup, and how it all relates to ethanol usage. It's pretty basic stuff for professional scientists, but it's something that most homebrewers learn at some point.

This post is about amylases -- enzymes that break down starch into sugar. They are a fairly important class of enzymes, as they happen to be the main enzyme that allows us to convert starches and other polysaccharides into simple sugars such as glucose that allow our bodies to run. The classic demonstration, used in elementary school science classes for decades, is to chew on a saltine cracker, Horace Fletcher-style, until the chewed cracker begins to become sweet; this is the result of amylases in your saliva (sometimes referred to in medspeak as "ptyalins") beginning the digestion process on the cracker, taking care of some of the heavy lifting that the digestive track would usually have to deal with.

Now as it happens, I'm a beer geek. I used to homebrew and probably will again, and the problem of breaking down starches into sugars is pretty much the most fundamental part of beer-making apart from the fermentation process itself. Unlike wine, beer is made from grains (usually barley, sometimes wheat), which consist primarily of starch instead of simple or disaccharide sugars such as maltose, fructose, or sucrose. The challenge of making beer is to break down those starches into smaller sugar units -- this is where the amylases come in, in a process called saccharification. There are several ways to do this, but the original is malting -- allowing the individual grain seeds to germinate just enough to make the harder starch soften to a more floury consistency, then drying the sprouted grain so that the process halts so that the resulting malt can be stored. When the grain is malted and dried at an appropriately low temperature, the amylases in the grain are preserved in active form and can be reactivated.

How, you may ask? Well, these enzymes are usually heat-activated, and since the dried malt is, well, dry, they also require a wet environment to work. In the very, very earliest days of civilization, the first brewers discovered that soaking malted grain in warm water (what we now call mashing) causes the starchy grain to grow sweet; in barley, at least, what is causing this is two different types of amylases. They both attack the same glucose-glucose linkages in a starch chain, but they work differently -- alpha-amylases attack at random, as often as not breaking of chains of three or more glucoses (trisaccharides and dextrins), while beta-amylases instead go for the end of the chain, nibbling off single glucose molecules. The two classes of enzymes work at different temperatures, with the practical effect of allowing the brewer to tweak the temperature to favor increased glucose production (thus a higher alcohol content) or increased dextrin production (thus creating a richer mouthfeel in the finished beer). Many of the differences between, say, a German pilsner and a British-style pale ale happen here, in the mashing stage. Temperature also has an additional role, in that heat "gelatinizes" the starch -- causes it to soak up water more than it would at room temperature, allowing the amylases more freedom to move and react. (Remember that; we'll come back to it.) Once the saccharification process is complete, the resulting sugary liquid, known to brewers as wort, is boiled with hops (this sterilizes the wort, which is extremely friendly to bacterial development) and cooled rapidly; after this, yeast is added, which transforms the sugar into ethanol, making beer.

When making corn syrup, the problem of saccharification is the same, but the methods are rather different, since corn is not usually malted like barley or wheat and doesn't have the same type of amylase activity. When the process was first discovered by a Russian chemist named Kirchof in 1811, the feedstock wasn't corn or barley but potato starch, and the saccharification agent was sulfuric acid; these days, however, enzymes derived from Aspergillus oryzae mold (the same mold that sake brewers use to make koji) are rather more common than acids in this application. In a manner similar to beer, it's possible to control the amylase action to change the proportion of long chains to single-sugar units, creating a range of possible consistencies and properties in the finished corn syrup; while most home chefs will be familiar with only Karo syrup and its relatives, the food industry has access to numerous variations of corn syrup with rather different applications (most relating to mouthfeel and keeping qualities). High-fructose corn syrup results from an even further enzymatic process that converts the free glucose units into fructose, which happens to be a sweeter isomer of glucose. As much of a bad rap as corn syrup has, it's cheap, not hard to make, and very, very useful, particularly in the confectionery business; it isn't going anywhere.

I mentioned earlier that heating the mixture would come back into the picture. Indeed, it's very hard to do a good job with enzymes on uncooked grains, and sake rice is always cooked before the koji and yeast are added (that's a separate and rather interesting process in and of itself, where saccharification and fermentation occur simultaneously). This is where we get to the current ethanol fiasco -- it's no secret that the push towards ethanol as an alternate fuel in the United States has been a disaster, but why this is an issue is seldom explained in the mass media. It's worth noting that Brazil has run its cars on majority-ethanol fuel mixtures for years, but there's two fundamental differences:

• Brazil has fewer cars than we do, and
  
• Brazilian ethanol comes from sugarcane, which is almost all sucrose (i.e. an easily fermentable disaccharide that doesn't need to be broken down); sugarcane ethanol breaks even in terms of energy expended.
  

The jury is still out on using cellulose (i.e. plant waste) for ethanol manufacture, but using cornstarch as feedstock adds an extra cooking step that the sugarcane process doesn't need. It's entirely possible at some point that someone may develop a super-koji that is capable of doing its work on uncooked starch in cold water, but so far no one's doing that. Sorghum is a good temperate-climate alternative for sugarcane in this process, but there isn't anywhere near enough of it under cultivation.

I have to admit to being one of the many people who thought corn ethanol seemed like a good idea at the time. We know now it isn't, and an awful lot of us jumped to conclusions without looking into the implications, but we have so much effort committed to it that it's hard to see how we're going to fix the problem. My recommendation would be to go have a beer and write a carefully worded, well-researched letter to your congresscritter.

If you'd like to read a little further on the subject, check out these references:

• Brewery.org, long the Internet's best reference on the science and practice of beer brewing.
  
• McGee, Harold, On Food and Cooking, 2ed. New York: Scribner, 2004, ISBN 0684800012. The second edition of one of the most significant inspirations for kitchen geekery, and the spiritual predecessor for the works of Alton Brown, Shirley Corriher, Cook's Illustrated magazine, and many others.
  
• Miller, Dave, Dave Miller's Homebrewing Guide. Pownal, VT: Storey Publishing, 1995, ISBN 0882669052. A general reference for home beer making which presents much of the biochemistry involved in brewing for a lay audience.