Alpha-amylase is an enzymatic bread improver that helps to increase the loaf volume, lowers the crumb firmness, and keeps bread fresh for longer. The technological function of amylase enzymes is to cleave starch molecules into small sugar subunits (dextrins) that the yeast can metabolize. The alpha- and beta-amylases, typically in combination with amyloglucosidase, are the most popular enzymes used in breadmaking. Alpha-amylases occur naturally in wheat flour, however, it is common to enhance their activity level by the addition of diastatic malt powder or fungal alpha-amylases.
Alpha-amylase is usually added to bread formulations at a concentration of 0.002–0.006 % (20 to 60 ppm) in relation to the flour weight. For easier dosage at home, it is recommended to use an all-purpose bread improver that includes alpha-amylase at the right concentration level. To achieve the best results, it is recommended to work with fungal alpha-amylases rather than cereal or bacterial amylases.
What do amylase enzymes do in bread dough?
Enzymes are proteins that catalyze (accelerate) chemical reactions. They are highly specific in both the reactions that they catalyze and in their choice of reactants. An enzyme usually catalyzes only one single chemical reaction.
Enzymes don’t get used up or broken down when they catalyze chemical reactions. They provide an active site to which the substrates of a reaction can bind to. After the chemical reaction has happened, the enzyme releases the reaction products and finds a new substrate to bind.
The substrate of amylase enzymes is starch. Amylases work like scissors that cleave dextrins off of starch polymers. Starch is nothing else than a long chain of glucose molecules. Amylases reduce the chain length of these glucose polymers. Short glucose chains are called dextrins. The most well-known dextrin is maltose. Maltose is a sugar consisting of two glucose molecules that are bound together.
If we add amyloglucosidase in combination with amylases to our dough, then we can cleave the starch chains down to single glucose units. Amyloglucosidase breaks down long-chain starch molecules and the dextrins generated by the amylases into the simple sugar glucose.
During mixing and fermentation of bread dough, the only starch susceptible to an attack by amylose enzymes is the damaged starch. Around 5-9 % of the starch in wheat flour gets damaged during the milling process. Damaged starch granules are broken down a thousand times more rapidly by enzymes than undamaged starch granules.
Why do we want to break down starch during dough fermentation?
First of all, simple sugars are food that the yeast metabolizes into carbon dioxide. High amylase activity in bread dough can speed up the fermentation because the yeast has plenty of sugar to consume. Adding to that, the bread browns better and faster in the oven the more dextrins you have in your dough. That is because dextrins like maltose are reducing sugars that react with amino acids from the wheat proteins at high oven temperatures to form dark flavor compounds. However, these are usually not the main reasons why exogenous amylases are added to bread dough.
The amylase activity also has some very interesting effects on the dough rheology, gelatinization, and retrogradation behavior of starch.
Many dextrins have a low molecular weight. As I have already discussed in my post about spelt flour, one of the main causes of dough stickiness is a large amount of low molecular weight compounds like dextrins. Alpha-amylases make the dough stickier because they cleave high-molecular starch polymers into low-molecular dextrins. This is an undesirable effect of amylases because it makes the dough harder to handle.
However, doughs prepared with alpha-amylase show more oven spring than plain wheat doughs without enzyme addition. The period of dough expansion in the oven gets prolonged. This is why alpha-amylase helps to increase the loaf volume.
To understand this phenomenon, we need to look at the network formation in bread dough during baking. When we talk about networks in bread making, we often talk about the gluten network but not so often about the starch network that gets formed when the starch gelatinizes in the hot oven.
Several factors influence the temperature at which starch gelatinizes, for example:
- the water content
- the pH value
- the fat content
- the salt and sugar concentration
And, most interesting for us:
- the amount of low molecular weight dextrins in the dough
Dextrins delay the gelatinization of starch by increasing the gelatinization temperature of wheat starch. A study by Spanish scientists showed that the gelatinization temperature of starch in a wheat dough with 66 % water and with 9 % added dextrins is 3 °C higher than the starch gelatinization temperature in a wheat dough without added dextrins.
Once the starch in bread dough gelatinizes, the dough viscosity increases, and the crumb structure remains fixed. The dough can’t expand anymore. The higher the starch gelatinization temperature, the more time the dough has to increase its volume in the oven. Thus bread doughs with added alpha-amylase show a better oven spring and thus lead to a larger bread volume.
Why do alpha-amylases delay bread staling?
Let’s get to the most important benefit of alpha-amylases: they keep the bread fresh for longer. Rearrangements in the starch fraction of bread are the most important factor that leads to bread staling. The starch retrogradation starts as soon as the bread comes out of the oven.
Starch is made up of two components: amylose and amylopectin. They are immiscible. They form two distinguishable phases in bread dough.
During cooling of freshly-baked bread, the amylose chains form helices, self-associate, and crystallize. Some of the amylose molecules also form complexes with the lipids in bread dough so that you end up with a permanent amylose network that consists of crystalline amylose and amylose-lipid complexes.
The other starch network in bread is the transient gelatinized amylopectin network that gets transformed into an extensive and permanent partially crystalline network during the storage of bread. This network continues to mature during storage. It increases in size and more and more amylopectin crystallizes.
The important factor here is not the crystallinity but the size and strength increase of the amylopectin network. The stronger this network, the firmer the bread. Also, water migrates away from the bread crumb to the crust and gets lost to the environment during storage. The bread gets dry and firm.
To delay bread staling, we need to change or inhibit the formation of the amylopectin network during storage. Amylases change the starch structure during fermentation because they cleave dextrins off the starch molecules. The starch molecules get shortened and form weaker networks. Also, the dextrins might get in between the amylopectin molecules during network formation and thus act as plasticizers.
However, the amylopectin network formation during bread storage is still only poorly understood and scientists haven’t decoded the exact starch network formation mechanism yet. We only know for certain that the amylase activity changes the starch structure and networks formed after the bread has been baked. As a result, the bread stays fresh for longer.
What are the different kinds of alpha-amylases used in bread making?
The three major alpha-amylases that are used in bread making are:
- Endogenous wheat alpha-amylase
- Bacterial alpha-amylase
- Fungal alpha-amylase
What is interesting for bakers is that these amylases possess different optimum temperature ranges, where their catalytic activity reaches a maximum, and different denaturation temperatures.
|Type of alpha-amylase||Optimum Temperature Range||Denaturation Temperature|
|Wheat||50-70 °C||80 °C|
|Bacterial||60-80 °C||90-100 °C|
|Fungal||55-60 °C||65 °C|
What we see here is that fungal alpha-amylases have the lowest optimum temperature range and lowest denaturation temperature. Fungal alpha-amylases get inactivated earlier into the baking process than endogenous wheat or bacterial alpha-amylases.
This prevents an excessive breakdown of the gelatinized starch during baking which can cause the crumb to become wet and sticky to the teeth. We call that “klitschige Krume” in German and it makes bread inedible. It’s disgusting.
You can observe this phenomenon at home: Bake bread with an overdose of traditionally produced diastatic malt powder and you will see how appallingly sticky the crumb is. With fungal alpha-amylases, there is a much lower risk for that to happen because these enzymes get inactivated earlier during baking. Fast inactivation of alpha-amylase is preferable in bread making.
Why I don’t use traditionally-produced diastatic malt powder
There is no good reason for working with diastatic malt powder instead of biotechnologically-produced enzymes nowadays. I only work with inactivated malt powder (“Aromamalz” ) for flavor and add biotechnologically-produced enzymes in the form of bread improver to the dough. That way you can be sure to consistently achieve the best results. The enzyme activity in traditionally-produced malt powder is imperfect and inconsistent.
In the old days, before fungal enzymes were widely and cheaply available, it did make sense to work with traditionally-produced diastatic malt powder. Because it was the only product on the market. But we don’t live in the stone age anymore. Nowadays, we can use inactive malt powder for flavor and add enzymes to it in the qualities and quantities that benefit our dough the most.
Actually, many diastatic malt powders on the market are produced in this way! I’m not kidding you. If you’re a food manufacturer, then you need to sell a consistent product that always behaves in the same way. The way to achieve that for baking malt producers is to heat inactivate the endogenous malt enzymes and to add exogenous enzymes in the desired quantities. Always check the label of the malt powder you buy. Products that are sold as “Goldmalz” (golden malt) in Germany are enriched with enzymes and other bread improvers. These are the malt products that I use and that I refer to as “bread improver” in my recipes.
One of my main motivations to write these posts is to provide a different viewpoint on bread making than all the other baking blogs out there. So many of these blogs are run by esoteric people that refuse to add “technical” enzymes and “unnatural chemistry” to their bread dough. This fairytale of the bad enzymes that degrade the quality and healthfulness of bread is bullshit. Avoiding fungal enzymes because you think they are toxic and take away from the flavor of the bread is delusional. The only acceptable reason to not add exogenous enzymes to bread dough is that you can’t buy them from a local store where you live or that you don’t bake often enough to always have them in your pantry.