Starch Damage: What it is, and what it means to milling and baking

05 August 20229 min reading

Starch damage, like many other aspects in baking, requires balance. If bakers and millers embrace starch damage not as a negative, but simply as a quality variable that can affect the consistency of their dough, our baking methods will only improve for the better.

Arnaud Dubat
Product & Application Director
Chopin Product Line with 
KPM Analytics

There is a clear misunderstanding in the baking and milling industry around the concept of “starch damage.” Certainly, the first reaction to many could be a negative – if I am damaging the starch, does that mean I am damaging my flour?

It is true: Starch damage does affect the behavior of dough during processing as well as the quality of the finished product. However, starch damage is a natural byproduct of the milling process. Whether or not your flour has too much or too little damaged starch is truly dependent on the milling intensity.

Although protein receives all the attention when it comes to describing flour quality, it is important to remember that flour is nearly 70-80% starch. And in fact, flour contains two types of starch: native starch, and damaged starch. But before going too deeply into the subject of starch damage and its impact on baking, it is important first to know where starch damage comes from. There are three variables that affect the amount of damaged starch in flour:

•Wheat hardness 

•The preparation of wheat for milling 

•The settings of the mill


One way to visualize how wheat is classified as “hard” or “soft” is to consider the construction of a brick wall. In this wall, the starch granules are the bricks, while the protein matrix of the endosperm of the wheat functions as the cement.

So, let’s go to our “wall” and try to break it down with a given force. If the cement (protein matrix) is strong and sets the bricks (starch) well, it is the bricks on the wall that will break. The more compact our bricks are, the debris will be larger.

On the other hand, if the cement does not set the bricks well, the wall is likely to break more easily, releasing the bricks without breaking them.

Figure 1. Anatomy of a grain

This principle was used to develop the original method for measuring wheat hardness called the Particle Size Index or “PSI.” This test consists of 3 steps:

1. Grinding the grain with a calibrated tool 

2. A sieving process for a fixed time

3. A weighing process of product that has passed through the sieve.

If there are fine particles passing through the sieve, it means the grain is more “resistant” to crushing, or “harder.”

But what does wheat hardness have to do with starch damage?

At equivalent an equivalent milling process, a “hard” wheat will produce flour with more damaged starch than a “soft” wheat. This extra damage will influence the quality of flours, most notably their hydration potential, the stickiness of dough, the fermentation, volume, and several other noticeable qualities on finished products.


The preparation of wheat (or conditioning) consists of mixing the wheat with a specific amount of water and then letting it rest. This process makes it easier for the endosperm and the outer layers of the grain (bran) to be parted during milling. 

The goal is to obtain the maximum amount of flour while minimizing ash content, and thus, the amount of bran in the flour. Water softens the endosperm, making it easier for the starch to be separated from the protein matrix. This results in less damaged starch.

Starch Damage Begins at the Mill

All milling, whether industrial or performed in a laboratory, will inevitably produce a certain amount of damaged starch. It occurs when wheat passes through two rollers, which are designed to crush the particles. The narrower of the gap between the rollers, the more likely the starch will be damaged.

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 glucose chains that make up starch)

The physical modification of the starch granule has very significant repercussion 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:

For our example, lets say we have a flour sample with an absorption potential that goes from 64% to 68%.

Possibility 1: More Bread can be Produced from the Same Quantity of Flour

• 1,000 kg of 64% flour leads to 1,640 kg of dough. This translates to 6,560 loaves weighing 250 g each

• 1,000 kg of 68% flour leads to 1,680 kg of dough. This translates to 6,720 loaves weighing 250 g each

• That’s 160 extra loaves that cost only the price of 40 liters of water!

Possibility 2: Less Flour can be Used to Produce a Set Amount of Bread

• 6,500 loaves made from 64% flour requires 1,625 kg of dough (991 kg of flour)

•  6,500 loaves made from 68% flour requires 1,625 kg of dough (964 kg of flour)

• That’s a savings of 27 kg of flour

Over time, this presents a significant financial impact on companies that produce large quantities of bread per hour.

Figure 3. Approximations of ideal levels of damaged starch (UCD) to produce common baked products.²

The second effect can be more problematic. Damaged starch may absorb more water, but it does not retain it nearly as well. In fact, damaged starch is very hygroscopic and absorbs water quickly. This explains its impact on water absorption potential.

However, during the mixing phase, the granules tend to release 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. 

This means there is an optimal balance to be found between the benefits of a higher hydration potential and a manufacturers’ need to avoid stickiness in their production line.

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

•When the yeast cannot use all of the sugar produced, the sugar stays in the dough and is more likely to contribute to caramelization after baking (known as the Maillard reaction) possibly leading to excessive browning of the bread’s crust during baking.

A fourth effect occurs in the oven. The carbon dioxide gas production 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.

One final effect can be seen on the finished product. If everything goes well during the baking process, 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 optimal level of starch damage, depending on the type of product, as well as the production process, as shown in Figure 3.

Functional analyzers exist today to measure damaged starch in flours. These technologies are fully-automated, enzyme-free, and produce reliable starch damage measurements in a short testing time period (~10 minutes) with a sample size of just one gram of flour. One example of this type of technology is the CHOPIN Technologies SDmatic, which was developed based on the recognized amperometric method (Medcalf and Gilles).

These analyzers help millers guarantee that the flours they are producing are according to the exact specifications of their customers. For the secondary processing industry, it is a cost-effective tool for raw material control and to predict and/or control processing and end-product quality.

From a baker’s perspective, being knowledgeable about starch damage and how it can influence their final product will be vital to ensure batch-to-batch consistency of their goods. It is also important to hold their millers accountable inquire about whether they are making starch damage control a part of their quality assurance program.

Nevertheless, starch damage, like many other aspects in baking, requires balance. If bakers and millers embrace starch damage not as a negative, but simply as a quality variable that can affect the consistency of their dough, our baking methods will only improve for the better. 


Mühle + Mischfutter, issue 9/2022, p. 15-17.

1. AACCi Method 55-30.01

2. D. G. Medcalf and K. A. Gilles “Determination of Starch damage by Rate of Iodine Absorption.” (1965) Cereal Chem 42:546 – 557.

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