The Science of Brewing
What are we doing here?
Most brewers out there can explain the basic principles of brewing. We are looking to convert barley starch into sugar, feed sugar to yeast, and separate the leftover sugar/alcohol mix. This blog is where we begin to dive a little deeper.
Barley for brewing (Hordeum vulgare) was selectively modified from wild barley (Hordeum spontaneum) to benefit enzymatic action when it was first culled for farming about 10,000 years ago. Since then, specific types and varieties have been carefully selected for traits such as growing conditions and starch content. Over time, these evolutions have reduced the starch cell wall thickness in brewing varieties. This reduction allows for better enzymatic hydrolysis (breaking of bonds by use of a water molecule and an enzyme) which in turn helps our end goal; extraction of sugar, flavor, and color.
After harvest, the barley kernels will have little enzymatic content and the remaining contents will be mostly insoluble. The maltster is responsible for fostering the development of more enzymes and they do this by way of steeping and germination. When hydrated, the seed uses its stored starch reserves in order to start growing. When malt processing begins, it stops this natural growth by way of kilning just as the seed created enough enzymes to begin cellular breakdown, but before the majority of starch is converted and used for growth. In reality, there is some overlap, and this mainly applies to base malts. The maltster must balance a compromise between enzyme production, convertible starch content, and flavor/color development. The responsibility of the brewer is to select the proper balance of malts for enzymatic activity, protein content, and total starch content. Don’t forget color, flavor, aroma, cost and availability too.
Around 1894 Emil Fischer hypothesized that enzymes fit together perfectly just like a lock and key. This is perhaps the simplest way to understand what is actually a complex set of reactions. By 1958, Daniel Koshland modified this theory, explaining the reactions as more of a “hand in glove” description. By his estimation, enzyme shapes are not entirely rigid, but rather flexible, and become fully formed during interactions with a specific substrate.
In either case, we understand there is a catalytic site where a reduction of required activation energy takes place (kickstarter to the reaction), as well as a binding site where the substrate is modified by the enzyme. Metallic ions and organic compounds can be suspended in an enzyme matrix, acting as a cofactor in the reaction of the enzyme, but this is not required in all enzymes.
When developing a recipe for a new product, it is important to think beyond starch content, color, flavor, and aroma. A top consideration should be the diastatic power of your grain, which represents the enzymatic activity level present in the malt. Without the proper diastatic power, you will not be able to access or convert starch into simple sugars that can be metabolized by the yeast. If you are using unmalted grains or or other forms of starch, supplemental enzymes or alternate processing techniques can significantly benefit your conversion and extraction.
Give me some sugar!
Hydrolysis of maltose, turning it into two molecules of alpha-glucose. The enzyme involved in this reaction is AMG (Amyloglucosidase or glucoamylase) which is present in Attenuzyme® Pro
The two major enzyme groups we are concerned with in mashing are both hydrolases, which means they make use of a water molecule to work their magic. Starch hydrolases such as alpha and beta-amylase are fairly well known as the workhorses, but less attention is often paid to the equally important cell wall hydrolases like beta-glucanase and xylanase. Together, these groups of enzymes will help solubilize the insoluble barley malt and allow for starch degradation into simple sugars.
The most pertinent enzymes for malting are located in the aleurone layer of cells that surround the endosperm (area in which the starch cells are located). During steeping and germination the kernel will increase enzyme content and activity, particularly in this aleurone layer. The increase in enzymatic activity will begin to degrade the starch cell walls, which are composed of a middle lamella encased on both sides by beta-glucan layers, which themselves are encased by pentosans. Modern quality malt is often degraded just enough to allow access to starch molecules, but not so much to destroy the physical properties of the lauter bed during processing, or to release unwanted organic acid compounds.
When using alternative starch sources or unmalted cereal grains, it is important to understand the need for enzymatic processing. If no “pre-digestion” of the cell walls has taken place, access to starch may need support. Gelatinisation of all starch molecules is a precondition for the enzymatic activity to do its work, but not all starch sources are as forgiving as malt. Corn, for instance, requires a higher gelatinisation temperature which will denature starch converting hydrolases before they can access the starch chains. This is why traditional brewing techniques would cereal cook, and then mix with malt at an appropriate temperature for amylase activity to degrade the total starch. When using undermodified or unmalted barley, another suggested method was to slowly and continually raise the temperature of the mashed grains to allow for optimal enzymatic development at each temperature range.
The term diastatic power is based on the studies of diastase, the first discovered enzyme. In 1833, when Louis Pasteur was roughly 10 years old, Jean-Francois Persoz and Anselme Payen published a study on the organic catalyst isolated from malt that was capable of converting starch into maltose.
If you aren’t up to speed on enzymes, here is one thing to remember - They are all ases (okay, not all, but a good majority since 1833). This means each enzyme is named after its substrate and ending in the phrase ase. Examples we will discuss include Maltose/Maltase, Glucose/Glucosidase, and Amylose/Amylase. So if you are thinking of alternative grains, unmalted barley, or other starch abundant sources, you better make sure to have a handful of ases if you want to play your cards right!
The next post will explain two very different mashing techniques targeting specific enzymatic conditions. In order to better explain the mashing process, a temperature styled timeline of enzymatic activity will be established showing some of the most important considerations in accessing and converting starches.