After discussing the main components of flour and how they will influence the baking processes, we will talk about the quality of flours, the most important parameters, and how to measure them. To do this, we will divide this topic into several entries because it’s quite important. Additionally, in the future, there will be specific posts about some of the most well-known equipment for quality control of flours.

And in this first entry, I believe we won’t address what most people would expect (aspects related to proteins, their baking quality, the suitability of flours for different preparations, etc.). On the contrary, we will talk about very important parameters that are sometimes overlooked, and problems that can render flours unsuitable for almost any product.

But don’t worry; we will also discuss proteins later.

The first thing to know is that there are no flours that are good for everything; instead, there are flours suitable for some uses and flours suitable for others. For example, a good flour for making Maria biscuits is very unsuitable for making sandwich bread, and vice versa. However, many people often hear about high-quality flours or wheat, and I’ve even used this term in some posts. When high-quality wheat or flour is mentioned, it usually refers to flours with a high protein content and a protein that forms strong but extensible gluten networks. These wheats or flours are more expensive and harder to obtain, which is why they are often referred to as higher quality, but they are not suitable for some uses. However, there are some aspects that make flours of poor quality for any use. These are the aspects we will address in this entry.

Moisture

The moisture content of flours is a key factor, and it’s regulated by legislation. In general, flours have moisture levels around 14-14.5%, with the legal limit being 15% (in Spain). In the milling process, it is necessary to add moisture to the wheat (conditioning) to soften it and separate the bran more effectively. Therefore, it’s logical for flour to have higher moisture content than wheat, and it should be relatively regular. However, it’s important to note that millers may want to sell water as if it were flour (at flour prices), so there is a legal limit to prevent abuse. Flours with higher moisture levels begin to have a risk of caking and, more importantly, the development of microorganisms, something that should be avoided at all costs.

Although it is not common for flours to have lower moisture levels, if they do, it can also pose a problem since formulas are adapted to a specific flour moisture content. For example, in a formula where flour accounts for 100 parts and water 50, assuming the flour moisture is 15%, you would have 65 parts of water and 85 parts of dry flour. If, on the other hand, the flour has 10% moisture, you would have 60 parts of water and 90 parts of flour. In the first case, water accounts for 76% of the flour, but in the second case, it’s only 67%, and therefore the formula should be adjusted.

Therefore, flour must have a moisture content below 15%, and it should be regular. As I mentioned, it’s typical for flour to have moisture content around 14-14.5%, but some flours from other cereals or grains, such as some gluten-free flours, may exhibit greater variability.

The official method for measuring the moisture content of flours is oven drying, but this method takes too much time, and time is money. Thus, in many industries, flour moisture is often controlled using thermobalances, which, although not an official method, typically provide accurate results. In flour mills, flour moisture is usually analysed using near-infrared (NIR) technology. These devices are very fast, but they require thorough calibration work. Due to the higher cost of the equipment and calibration, and because the calibration needs to be specific for each product type, these devices are commonly used in factories that deal with very specific products (the same product in large quantities), such as dairy companies, flour mills, wineries, etc. These devices have the advantage of analysing multiple parameters in seconds. In the flour industry, they are often used for calculating moisture and protein content, among other components.

Particle Size

The particle size of flours is another crucial factor that is often overlooked. Wheat is a soft cereal and generally produces fine flours. Regulations state that white flour must have a particle size where 90% passes through a 180-micron sieve, but typically, wheat flours have an average particle size of around 100 microns. However, there can be significant differences in particle size for other cereals, and not all 100-micron particle size flours are equal. For products where gluten network formation is essential, the typical wheat flour particle size does not pose problems. There are only a few cases, such as in the production of certain cakes, where a slightly finer particle size may yield better results. This can be achieved by using softer wheat varieties, selecting specific milling passes, or even micronizing the flour. In some types of cookies, particle size can also be influential, so it would be desirable for it to be at least consistent among different batches.

In the case of gluten-free flours, differences in particle size are often much more pronounced, and their influence on the quality of the final product is also greater. In general, gluten-free grains are harder than wheat and tend to produce coarser flours. However, this particle size can be reduced through milling processes, resulting in different flours based on their particle size. Cakes and batters often benefit from finer flours, and in the case of gluten-free bread, coarser flours often yield larger bread volumes for the same hydration of the dough (finer flours require more hydration) but may generate a sandy texture. For cookies, coarse flours yield cookies that expand more in the oven and have a less firm texture, but a small amount of fine flour is necessary to provide cohesion to the dough. However, when attempting to reduce the particle size of these flours, a greater amount of damaged starch can also be generated, altering the flour’s characteristics. As you can see, it’s a complex issue, but the key takeaway is that particle size is important, especially in gluten-free flours.

In the case of whole-grain flours, the particle size of the bran is also crucial, but we will discuss this issue in another entry.

By the way, particle size is often analysed using sieve sets, but there are more sophisticated (and much more expensive) devices, such as the MasterSizer, which provide more precise data.

Ash Content

The ash content of white flour is an indicator of possible bran contamination. During the flour-making process, efforts are made to separate the endosperm from the bran as effectively as possible to prevent bran “contaminate” the endosperm. Since bran has a higher ash content than the endosperm, a high ash content typically indicates that some bran has entered the flour. In fact, many countries have official flour classifications that take ash content into account. In general, flours should have ash content lower than 0.55-0.65%, with slightly higher levels in bread flours.

Another possible reason for increased ash content in flours is the inclusion of additives, as some additives can increase the ash content of flours. However, in the case of pure, unadulterated flours, high ash content typically indicates a high degree of extraction (obtaining more flour per kilogram of wheat) and contamination with bran. Therefore, a flour should have low ash content since bran contamination is detrimental to flour quality.

To measure ash content, samples are typically subjected to high-temperature combustion (between 500 and 600°C) in muffle furnaces. However, reliable data can also be obtained using NIR technology.

Germination

When a grain germinates, many enzymes are activated to break down the components of the endosperm to provide nourishment to the new plant in its early stages. This phenomenon, which can be harnessed for brewing and alcoholic beverages (malting), is typically detrimental to the baking quality of flours, and unless it is a controlled process, it will be detrimental to any use of flours. During this process, in addition to amylases, proteases are generated, which break down the proteins responsible for forming the gluten network, thereby preventing the formation of that protein network or weakening it. Other enzymes are also generated that act on fibres, lipids, and other grain components, altering the characteristics of the flours. The enzymatic level of flours depends on the extent of the germination process.

In general, flours from germinated grains have less thickening power, produce weaker doughs, result in darker bread (due to increased sugar production), and less consistent crumbs (due to starch hydrolysis). We will discuss enzymes and their role in baking in more detail in another entry. The main problem is that this germination, when it occurs in the field, is not controlled, and there is a lot of heterogeneity between batches.

The issue of germinated grains is more common in northern European countries and other areas where, once the grain matures, there are conditions of high humidity, and it is necessary to delay grain harvesting for various reasons. This is because grain needs moisture to start germinating in the spike.

To detect this problem, the falling number analysis is often used. This equipment subjects a mixture of flour and water to controlled heating to gelatinize the starch with minimal damage to enzymatic activity. After this process, a very thick, almost gel-like paste is formed. Subsequently, the equipment allows the mixture to be degraded by the amylases present, measuring the time it takes for a rod to descend a certain distance through the formed gel. The shorter the time, the greater the enzymatic (amylase) activity of the flour, as the gel is hydrolysed more rapidly, indicating the presence of germinated wheat. In general, levels of 250-350 are suitable for baking. Lower levels indicate problems with high enzymatic activity, and higher levels indicate the need to supplement formulas with amylases, which are typically included in various improvers.

Protein Degradation

Another problem that flours can have, significantly reducing their quality, is protein degradation. This problem occurs when wheat has been attacked by bugs, known as cereal bugs. The term “cereal bugs” is used as if it were a single insect, but it can refer to different insects, as Aelia and Eurygaster. In Spain Aelia is more commonly referred to as “garrapatillo” or “paulilla,” while Eurygaster is often called “sampedrito.” However, as I mentioned, the term “cereal bug” is sometimes used interchangeably. These insects feed on the wheat grain when it is in the milky stage (before hardening during the maturation process). To do this, they have a trumpet-shaped mouthpart that they insert into the grain. To feed on the grain’s components, they inject a complex of enzymes that hydrolyse these components, making them more easily digestible. The problem is that these enzymes remain in the grain, and when these grains are used to make flour, even a small amount, less than 5%, can damage all the flour produced.

Both Aelia and Eurygaster. Source: wikipedia

The most well-known effects of cereal bug infestation are related to protein degradation because among the enzymes injected into the grain are proteases. However, other enzymes that act on fibres, lipids, and other components of the grain are also present. This degradation is progressive and increases over time, so it will be greater in fermentation processes where there is more time for the enzymes to act, than in the production of products like cakes, where the dough is processed more quickly. However, this problem affects the quality of the flour for almost any use and is especially important in products where gluten (protein network) plays a significant role, such as bread.

Interestingly, if the insect attack has been severe, the grains appear shrivelled and small, and they are discarded in the cleaning process. But if the attack was not severe, meaning the enzymes were injected but the insect did not fully feed on the grain or did so to a limited extent, these grains may show a puncture or a mark but are not discarded during grain cleaning.

An additional problem with cereal bug infestation is its difficult detection. In principle, as mentioned earlier, grains with cereal bug infestation usually have punctures or black spots, but it is impractical to inspect each grain individually when a batch arrives. Common analyses conducted on wheat when it enters a flour mill do not detect this problem because they are generally rapid analyses, and detecting this problem requires letting the enzymes act. Although attempts have been made to develop rapid methods, the detection method for protein degradation in Spain is the alveographic analysis. This involves performing an initial analysis and a second analysis after 2 hours, comparing the results of both. If the alveographic curve has reduced in length (extensibility of the flour) and area (flour strength) over time, it is considered to have cereal bug infestation, and these flours should be discarded.

Wheat grains with cereal bug infestation

In the baking processes, something similar would occur, as this attack would not be evident during the kneading, especially if it is done quickly, but it would lead to the collapse of the dough during fermentation, when the enzymes have the time and the right temperature to act on the dough components.

Infestation by cereal bugs is more typical of Mediterranean countries and not found in other parts of the world. This problem depends on climatic conditions and whether field treatments have been carried out to combat this pest. In New Zealand, a similar problem has been reported, but it is caused by another insect (nysius).

Nysius. Source: wikipedia

Traditionally, monocalcium phosphate has been used as an additive to combat the effects of cereal bug infestation. This additive is a chelating agent and acts by sequestering metal ions. The proteases present in the grain appear to be metalloproteases, a specific type that requires the presence of metal ions to function. By sequestering the metal ions, the action of the proteases is minimized, but this is only effective if protein degradation is not too advanced. There are more potent chelating agents, such as EDTA, that may be more effective, but their use is not permitted in flour production. In any case, batches of wheat with protein degradation should be discarded to produce flours intended for human consumption.