36 Enzymes
Enzymes are not ingredients as such, but they are present in other ingredients, chief among them are flour and yeast. Understanding how enzymes work is very helpful in understanding fermentation.
Enzymes are as unique as fingerprints. They can be defined as minute substances produced by living organisms that bring about or speed up certain chemical changes. For example, enzymes act in the human digestive tract to break down food.
The action of enzymes is specific, and each class of enzymes has only one particular chemical conversion that it will bring about. For example, one kind of enzyme converts sugar into carbon dioxide and alcohol, and this is the only direct function it can perform.
A clue to recognizing enzymes is by the ending of their names, which usually is ase as in maltase. The sugar that maltase works on ends in ose as in maltose. There are a few exceptions; for example, papain, present in papaya and used as a tenderizer, is also an enzyme.
Sometimes the terms are confusing. For example, the two enzymes amylase and diastase work in such a similar way that they can be thought of as the same for the purposes of baking. Both these enzymes work on starch. Sometimes books refer to amylolytic activity, to refer to the work done by amylase, and sometimes they refer to diastatic activity to refer to the work done by the diastase. For convenience, in this book we use the term diastatic as much as possible.
Enzymes Present in Flour
Enzymes present in flour are diastase/amylase and protease.
Diastase/Amylase
Under the right conditions, diastase will break up some starch, liquefy it, and convert it into malt sugar. This provides food for the yeast and sugars that help to brown the loaf later on in baking. It is a very important function in lean dough where little or no sugar has been added. Diastase or amylase is destroyed at 77°C (170°F) during baking, at which point the dough stops expanding.
At the flour mill, one of the laboratory tasks is to determine if the grain has the correct balance of enzymes. Either too few or too many can affect the handling and fermentation of dough. One problem when too many enzymes are present is evident in rye flour, where the integrity of the starch is especially important.
The amount of diastase in grain varies from year to year, depending on harvest conditions. In a damp harvest season, the grain may start to sprout, which is a signal for enzymes to become active. The starch from such grain is said to be damaged, which is not a completely bad thing, as a certain amount of damaged starch is desirable to provide yeast food. The miller adjusts this level, if necessary, by adding amylase, and blending flours.
Protease
Protease is found in flour, but also in malt and yeast. Protease converts a portion of protein that cannot be dissolved in water into another form, which will dissolve in water. In this condition, the protein can be used by yeast as food. The protein makes the gluten more elastic by softening it, and produces amino acids (see Figure 8).
Protease starts to work immediately after the dough is mixed. It is instrumental in imparting good flavour and digestibility to the baked bread.
Enzymes Present in Yeast
The two principal enzymes present in yeast are maltase and invertase. In addition, there are several other minor enzymes in yeast, each of which contributes in some way to the total changes brought about by yeast activity in the dough. Some of these changes assist in imparting flavour and digestibility to the finished bread.
Maltase
Maltase changes malt sugar (also known as maltose) into simple sugar.
Invertase
Invertase converts cane sugar into simple sugar. This enzyme only has work to do if granulated cane sugar has been added to the dough. It does not break down maltose, for example.
Zymase
Zymase works on simple sugar that has been produced by the action of invertase and maltase. Zymase changes the simple sugar into alcohol and carbon dioxide gas, which causes dough to rise and expand (see Figure 9).
In summary, enzymes work in fermented dough to effect starch reduction and sugar production. This enables the yeast to thrive and produce carbon dioxide, which leavens the bread. Each enzyme has a particular job to do. The enzyme level is checked at the mill laboratory, and flour delivered to the baker is generally perfectly balanced with the correct level for reliable fermentation.