St. Patty’s Post: Beerzymes (Alpha & Beta Amylase)

Happy St. Patrick’s Day!

EDIT: This was obviously supposed to post on March 17th

Personally, this is one of my favorite holidays. Cured meats, good beer, and stories of missionaries driving snakes (an obvious metaphor for Irish druidism) from Ireland – what more could you possibly want?

In the spirit of the holiday, I’m going to showcase two interesting enzymes (or beerzymes as I whimsically and somewhat superfluously call them) that are necessary for the fermentation process of brewing beer – α(alpha) and β(beta) amylase [AM-uh-lace].

First – what’s an enzyme? An enzyme is specialized molecule, or protein, that biological systems use to perform certain functions. For example, in the process wherein our cells divide, the DNA housed inside our nuclei must be replicated for use in the “new” cell. This process requires the action of a DNA helicase, which is an enzyme that partially unravels the DNA double helix such that the cell’s replicative machinery can get in and do its job.

Enzymes have many functions. The function of the class of enzymes known as amylases is to break down starch and glycogen, both of which are glucose polymers (molecules consisting of repeating units of glucose molecules), by hydrolyzing [HI-dro-LIZE] or “cutting” the chemical bonds that glucose polymers use to link glucose, the α1→4 glycosidic [GLY-co-SID-ick] bond.  The human body naturally produces amylases for all sorts of purposes such as when α-amylase is secreted from the salivary glands to aid in the breakdown of starchy foods like rice and potatoes. Fun fact: amylases were the first class of enzymes to be discovered via the work of Anselme Payen in the early 1800s.

2xfr b amylase.png
Structural representation of the enzyme beta-amylase from barley.1

So what do these enzymes do for beer?

Well, the first step in the production of is creating a mash, or a sort of “tea” using mashed grains and hot water. Mashing grains releases starches into the water, becoming a mixture called the ‘wort’. Typically, many of these sugars released, at the beginning of the process, are not fermentable, meaning, they cannot be digested by yeast to produce alcohol. In order for these sugars to be fermentable, they need to be broken down into smaller constituents, the monosaccharide glucose and the disaccharide maltose. Once this is done, the yeast that is added to the wort can begin digesting the sugars, starting the process of fermentation.

More information about carbohydrates here.
File:Starch-breakdown-sites.jpg
Diagram showing the action sites of alpha and beta amylasae on a starch molecule. Courtesy of Wikibooks user Lrh.

Not all amylases are the same, alpha and beta amylases perform similar but different jobs. Alpha amylases hydrolyze [HI-dro-LIZE] or “cut” glycosidic bonds in random areas along the glucose chain, eventually degrading the starch completely into individual glucose molecules. Beta amylases, however, can only hydrolyze every other glycosidic bond, forming maltose.

At the end of the mashing period, the wort contains (from the alpha-amylase) and maltose (from the beta-amylase), two principal sugars used in fermentation. The wort will also contain a considerable amount of glucose-1-phosphate, a phosphate-linked sugar that is a product of the alpha-amylase function. Yeast cannot internalize glucose-1-phosphate, thus those glucose molecules are non-fermentable. This means that beta-amylase largely produces the greatest amount of fermentable sugars.

Being that these two enzymes produce different, useful products, brew masters can manipulate their ratios of use their characteristics to their liking. The relative levels of the enzymes can be controlled by the temperature level of the mash as the two enzymes have differing optimal temperatures.

Alpha-amylase functions at temperatures between 145° to 158° F, while beta-amylase operates between 131° and 149° F.2 Therefore, if you want to increase the amount of easily fermentable sugars, increasing the amount of alcohol in the final product as the yeast are able to consume more, you would want to mash your grains at temperatures optimal for the function of beta-amylase. If you want to maintain some of the sweetness of the sugar in your brew, you would run past the beta-amylase’s optimal temperature and mash within alpha-amylase’s optimal temperature range.

References

  1. Rejzek, M.; Stevenson, C. E.; Southard, A. M.; Stanley, D.; Denyer, K.; Smith, A. M.; Naldrett, M. J.; Lawson, D. M.; Field, R. A. (2011). “Chemical genetics and cereal starch metabolism: Structural basis of the non-covalent and covalent inhibition of barley β-amylase”. Molecular BioSystems. 7 (3): 718–730.
  2. Parkes, S. (n.d.). Understanding Enzymes: Homebrew Science. Retrieved from http://byo.com/hops/item/1543-understanding-enzymes-homebrew-science

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