Although protein receives all the attention when it comes to describing flour quality, it's important to remember that flour is nearly 70-80% starch.

Flour contains two types of starch: intact and damaged starch.

All milling, whether industrial or performed in a laboratory, will inevitably produce a certain amount of damaged starch. When we look at the behavior of a damaged starch granule compared to that of a native granule, we see that:

  • Its water absorption capacity has been multiplied by nearly 10,
  • It is much more susceptible to hydrolysis by amylase (an enzyme with the capacity to break down the glucose chains that make up starch).

This physical modification of the starch granule has very significant repercussions for the baking industry.

The initial effect is fairly positive. It increases the water absorption potential of flours, sometimes by several percentage points.

The economic impact may also be significant, and can be looked at in two ways. Let's take the example of a flour with an absorption potential that goes from 64% to 67%[1]:

  • Possibility 1: More bread can be produced from the same quantity of flour.
  • ~1,000 kg of 64% flour à 1,640 kg of dough à 6,560 loaves, weighing 250 g each[2]
  • ~1,000 kg of 68% flour à 1,680 kg of dough à 6,720 loaves, weighing 250 g each

That's 160 extra loaves that cost only the price of the water.

  • Possibility 2: Less flour can be used to produce a set amount of bread.
  • ~6,500 loaves made from 64% flour à require 1,625 kg of dough à 991 kg of flour
  • ~6,500 loaves made from 68% flour à require 1,625 kg of dough à 964 kg of flour

That's a savings of 27 kg of flour.

It's easy to see that the financial impact for companies that produce large quantities of bread per hour, is significant.

The second effect can be more problematic. The damaged starch may absorb more water, but it doesn't retain it nearly as well. In fact, damaged starch is very hygroscopic and absorbs water quickly (which explains its impact on absorption potential). However, during the mixing phase the granules tend to release that water again. At first, the freed water will be soaked up by the protein, a significant component in the dough, to complete its hydration. But if water continues to escape from the damaged starch granules once the protein is fully hydrated, it will separate from the dough and cause stickiness. A balance has to be found between the protein level and the starch damage.

  • There is an optimum to be found between the benefits of a higher hydration potential and manufacturers' need to avoid stickiness in their production lines.

The third effect takes place during fermentation. It's easier for amylase to break down a damaged starch granule. This results in higher sugar production, which leads to several phenomena:

  • The activation of carbon dioxide gas production. This causes the dough to rise, which will increase the volume of the bread as long as the protein network is able to retain the gas. Excessive gas production can create too much pressure, making the dough porous and unstable. The phenomenon is amplified in the oven, where the heat causes the gas to expand. We are then likely to see the structure fall, resulting in low-volume loaves even though the dough rose well.
  • When the yeast can't use all the sugar produced, the sugar stays in the dough and is more likely to contribute to caramelization or a Maillard reaction, possibly leading to excessive browning of the bread's crust.

One final effect can be noted in the finished product. If everything goes well during bread production, the water absorbed by the damaged starch will be released very slowly, improving the freshness and shelf life of the bread.

It's easy to see that for the baking industry, the key phrase for damaged starch is “not too much and not too little.” There is an optimum, depending on the type of product as well as the production process (Figure 1). In any case, all we can do is consider the impact that damaged starch may have on final product quality, and recognize the importance of measuring it.

Figure 1: Optimum starch damage for various grain products. (relationship between protein levels and optimum starch damage)

[1] To simplify, these calculations only include flour and water.Yeast, salt and other ingredients are not taken into account in this example.

[2] Mass of dough prior to baking.

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