E – for Enzymes

What are enzymes?

Enzymes are mostly proteins that, as biocatalysts, can accelerate certain chemical reactions without being altered themselves. All enzymes have the suffix "ase" in common.

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Where are enzymes located?

Certain enzymes are already present in barley. However, they are usually in a dormant, i.e., inactive, state. During germination, they are awakened or activated. The majority of enzymes are therefore formed during the malting process in the germination phase within the barley grain.

What is the purpose of enzymes?

The purpose of enzymes is to break down the starch contained in barley into small, fermentable sugars so that, in the next step of whisky production – fermentation or alcoholic fermentation – these can be converted into alcohol by yeast.

What is starch?

Starch is a widespread organic biomolecule in the plant world and is present in barley at a concentration of about 60 percent. It is a giant or macromolecule – in the form of a polysaccharide – which is exclusively composed of the single building block glucose. The individual glucose units link together at a specific point in the molecule, forming long sugar chains that coil into a spiral. This spiral-shaped giant structure is called amylose. However, the glucose units can also connect with their neighbors at another point in the molecule. This creates long sugar chains with extensive branching. This branched form is called amylopectin. Starch consists of approximately 20 to 30 percent amylose and 70 to 80 percent amylopectin.

How does the biochemical breakdown of starch work?

Let's mentally cut through a barley grain. We observe small spheres, called starch granules, surrounded by a protective layer and embedded in a protein matrix. First, these starch granules must be exposed. To do this, a specific class of enzymes, the cytases, biochemically break down the starch-encasing protective layer. The protein matrix, in which the starch granules are embedded, is broken down with the help of so-called proteinases. The breakdown products of these enzymes are various amino acids, which in turn are needed as a nutrient and growth source for the yeast during later fermentation. The exposed and now accessible starch granules can be broken down into smaller fragments by a third class of enzymes, the amylases. Alpha-amylase breaks down the long glucose chains of starch into smaller fragments, called dextrins, as well as into sugars with lower molecular weight. Beta-amylase, on the other hand, always cuts off exactly two connected glucose molecules (= maltose) from the end of a sugar chain. Alpha-glucosidase, in turn, only removes a single glucose molecule from the ends of the sugar chains, while limit dextrinase cleaves the branches in the amylopectin of the starch. The shorter sugar chains formed in this process can be further broken down by the other enzymes into fermentable sugar building blocks in the same way.

At what temperature do enzymes work?

Generally, the enzymes relevant for mashing work at temperatures between 40°C and 80°C, with each enzyme or enzyme class having its own optimal temperature range within which biochemical processes occur as quickly as possible and with high yield. This means that for the enzymatic breakdown of starch, both a specific temperature and a specific time are the decisive parameters and thus play an enormously important role for an optimal mashing process. The temperature optimum for some of the starch-degrading enzymes is 62°C to 65°C, which roughly corresponds to the temperature of the first mash water. This high temperature causes the starch granules to swell and burst (= gelatinization), thus facilitating the enzymes' access to the starch and its breakdown. After an exposure time of about 30 minutes, the formed, sugary wort is drained through the sieve bottom of the lauter tun – the mash tun – while fresh water at a now higher temperature is added from above. This has the crucial background that any remaining starch granules in the barley are also gelatinized and thus made accessible to the enzymes.

What happens to enzymes at higher temperatures?

Not all enzymes survive the higher temperature. But those that are not immediately thermally inactivated take the remaining opportunity to break down further starch into smaller sugar molecules.

What are the temperature optima for mashing enzymes?

Alpha-amylase is stable in a temperature range of 65°C to 75°C. The other enzymes are somewhat less heat-stable and denature earlier over time. Thus, the temperature optimum for beta-amylase is 60-65°C, for limit dextrinase it is 55-60°C, and for alpha-glucosidase it is below 45°C.

How much starch is converted to sugar?

At the end of mashing, approximately 80 percent of the starch has been converted into fermentable sugars through enzymatic breakdown.

What role does the protein content in barley play?

The protein content in barley grain should not be too high, as a lot of protein simultaneously means less starch, which in turn means less sugar, ultimately leading to less alcohol. However, the protein content should also not be too low, as the yeast needs the amino acids broken down from the proteins with the help of proteinases as a nutrient and growth source. A protein content of about 10 percent in the barley grain has emerged as a reasonable compromise.