Yet people are getting 88%. That's really the question. How to get those high values.
Brewers control attenuation via a combination of yeast selection and wort composition. As long as the yeast strain can handle the ethanol stress, a yeast culture will chew through all of the sugars that it can reduce to hexoses (monosaccharides). The trick is to minimize the amount of dextrin and trisaccharides in the wort. Yeast cells consume sugars more complex than glucose by breaking something known as glycosidic bonds. They perform this feat by producing enzymes. Enzymes are reaction catalysts. A reaction catalyst is a compound that speeds a reaction.
Let's look at how a yeast cell consumes a molecule of the trisaccharide maltotriose. It starts by splitting it into one maltose molecule and one glucose (monosaccharide) molecule. It then splits the maltose molecule into two glucose molecule. The process of splitting more complex sugars into simpler sugars is called hydrolysis. The roots in hydrolysis are "hydro" and "lysis." Hydro is from the Greek word "hydros," which means water. Lysis is Latin for break apart. Hence, together they mean break apart using water, and that's exactly what happens. The enzymes merely speed the rate at which the reaction occurs.
The chemical formula for maltotriose is C
18H
32O
16.
C
18H
32O
16 + H
2O → C
12H
22O
11 + C
6H
12O
6The reaction shown above reads one molecule of maltotriose combined with one molecule of water yields one molecule of maltose and one molecule of glucose. The yeast cell can use the molecule of glucose directly.
The cell then goes about breaking the bond that holds the two glucose molecules in maltose together.
C
12H
22O
11 + H
2O → C
6H
12O
6 + C
6H
12O
6The reaction shown above reads one molecule of maltose combined with one molecule of water yields two molecules of glucose.
If we move up in the process, what do you think mashing is from a biochemical point of view? Well, it is the hydrolysis of starch. The hot liquor in a mash provides the water molecules. The enzymes limit dextrinase, alpha amylase, and beta amylase are the reaction catalysts in the hydrolysis of starch. Each of these enzymes breaks a different glycosidic bond. We control the effectiveness of each enzyme by controlling the mash temperature. A lower mash temperature yields a more fermentable wort because it produces a wort with a higher monosaccharide and disaccharide to trisaccharide and dextrin ratio. It does so by striking a balance between the different enzymes.
Sucrose is a disaccharide that has the same chemical formula as maltose. However it is composed of one molecule of glucose and one molecule of fructose. We have all more likely heard of something known as invert sugar. Invert sugar is an integral component in many British beers. Invert sugar is sucrose with the glycosidic bond that holds the glucose and the fructose molecules together broken, which is why it is more readily fermented than straight table sugar. Belgian candi sugar is invert sugar.