How to Determine The Quality of Wheat (Flour)

The simplest of breads are made with just water and flour (such as a chapati). Add a little yeast and maybe some salt or fat and you can make a wide range of breads from a wide range of cultures and countries. Since bread can be so simple, a lot of it comes down to its major ingredient: flour. If that flour doesn’t behave as it’s to, your bread can fail quite miserably.

It is something most of us might not even think of, since it’s so normal to just buy a bag of flour in the store. However, did you know that most wheat varieties aren’t even suitable for baking! Some don’t contain the right amount of protein (gluten), others don’t grow well, yet again others don’t taste good.

It’s why wheat breeders extensively test their (new) wheat varieties before deciding which ones to use. So how do they and farmers, decide which varieties are most suitable for use in our breads and other flour-based products?

Composition of wheat (flour)

Most researchers will start by analyzing what’s in the wheat kernel itself. Knowing how much moisture, protein and ash is in wheat and the resulting flour will help determine what that flour may be used for.

Just how wheat will behave depends to a large extent on its composition. Just what exactly that wheat kernel is made up of determines how it will behave. All the different molecules have different roles in flavor and wheat behavior.

Moisture content

Most foods contain water, even if they look dry, and wheat is no different. It is very important that wheat is not too wet to prevent the growth of undesirable microorganisms. Farmers and millers aim for a moisture content of about 14% in the wheat. At values of >14,5% molds and other undesirable microorganisms stand a good chance of growing in wheat kernels.

A farmer controls moisture by harvesting when the wheat is dry and under favorable weather conditions. Some farmers may dry their grains after harvest before storage, depending on the moisture content of the kernels, to ensure they stay well.

Apart from food safety considerations, the moisture content also impacts the milling of wheat kernels. If kernels are too dry it can become challenging to mill them, since they will be harder. As such, a miller prefers a very consistent moisture content.

Lastly, an important reason for measuring moisture is that a lot of other analytical methods are done on the dry material. In other words, moisture may be removed first, before analyzing the content of a certain component. It is then very important to know the moisture content, so the overall content of the component in the complete kernel can be calculated.

Moisture content can be measured by drying the wheat and measuring how much weight the kernel has lost. Alternatively, laboratories might use an NIR (near infrared spectroscopy).

Protein content

Next up, the protein content. The proteins in wheat flour are mostly gluten proteins. They have an enormous impact on how wheat will behave when transformed into bread (or noodles or cakes for that matter).

Whereas you don’t want a lot of gluten for making cakes or cookies, you do want a good amount of gluten for making most breads. The protein content of wheat flour can vary drastically though, from as low as 6 to as high as 20%. Depending on your type of bread, you’re looking for a protein content of about 9-15%.

Protein content can be measured using various ways, for example by using the Kjeldahl method, combustion, and again NIR. Remember, this analysis only gives you the quantity of protein. It doesn’t tell you anything about the quality of the protein!

Ash content

The last common compositional analysis is ash content. Wheat is made up of mostly starch, water, protein, fibers and some fat. These are all so-called organic components. However, wheat also contains a smaller fraction of inorganic components such as minerals (e.g. iron and zinc). These are all captured together in the ash content of the flour and make up approximately 1% of wheat.

Most of the ‘ash’ is contained in the bran of a wheat kernel (see illustration above). During milling, the bran layers are often separated from the endosperm to create white flour. As such, this measure is used to help quantify just how much of the kernel was used for making the flour. Very white (high extraction rate) flours contain none of the bran so will have very low ash content. Wholewheat flours on the other hand, that are made of the whole wheat kernel, contain a lot more ash. We’ve compared more flours in a separate post.

To measure the ash content, the flour sample is completely incinerated. All that’s left are the inorganic components, allowing the analyst to determine just how much there is left.

Behavior of wheat flour

Knowing the composition of your wheat gives millers and bakers a first idea of how that wheat will behave. However, just how that flour behaves isn’t clear yet. It’s why several tests have been developed over the years to do just that. Simple tests, demonstrating a specific behavior of the flour, without having to bake a wide variety of products!

Testing enzyme activity

A wheat kernel is the seed of a plant. Normally, under the right conditions (and if we wouldn’t eat the wheat), it sprouts to form a new wheat plant! This can happen as well when you don’t store wheat kernels properly, for example in a humid environment. When kernels start to sprout, all sorts of chemical reactions are initiated, including the activation of α-amylase enzymes.

Alpha-amylase enzymes break down starches in the wheat. For some applications, such as beer brewing this is very desirable. In other instances, having too many active enzymes is highly undesirable. For most breads, you’d want some active enzymes. The enzymes improve the shelf life and structure of bread (e.g. they can delay staling). Also, by breaking down some of the strach in smaller sugars, they ensure there’s enough ‘food’ for the yeast to grow on during proofing.

As such it is important for users of wheat flour to know just how much their wheat has started to sprout. It is expensive to measure the exact activity of enzymes, but luckily there are some simple tests that give a good indication of the activity of the enzyme.

Falling number

If you mix water and flour you’ll get a paste/gel like system. This thick consistency is for a big part influenced by the starch in the flour. A lot of intact starch will make the paste thicker. If enzymes have broken down a lot of the starch, the paste will be a lot thinner. Miller and bakers use this concept to test for enzyme activity by determining the ‘falling number’.

For this test water and flour are mixed and held at a constant temperature for a set amount of time. During this time the enzyme gets to work and starts to break down starches. At the end of the set time a probe is dropped into the flour + water mixture. The test measures just how long it takes for that probe to reach the bottom. This time, measured in seconds, is what bakers and millers call the falling number of a flour. It is an indirect measurement for the amount of active enzymes.

A falling number value lower than 150s means the probe fell through really quickly. As such, it means there is a lot of enzyme activity. At this low a value wheat is unsuitable for most applications. If the value is higher than 400s no meaningful amylase activity is present. Anywhere in between means there is activity to a varying degree. As mentioned above, it depends on your application which falling number is acceptable. For regular store-bought flour the falling number has set specification limits, ensuring consistency.

Other methods for enzyme activity

The falling number is one of the older methods available to determine enzyme activity, but is widely used. There are several other methods available, that all work more or less the same way, with slight tweaks. Examples of such methods are an amylograph, rapid visco analyzer or using amylazyme all measure the same thing, but in a slightly different way.

Protein Quality & Dough Consistency

Gluten play a very important role when making bread. Without the gluten your dough wouldn’t be as stretchy and able to puff up nicely in the oven. Gluten proteins are made up of a mixture of proteins and their ratios and quantities will impact how well gluten works.

You can easily measure the overall quantity of proteins, however, you can’t measure exactly whether these proteins are of the right quality. As such, tests have been developed that can give a verdict over the quality of the proteins, by how the flour behaves in the tests!

Farinograph & Mixograph

One such way is to use a mixograph or alveograph, both of which are very similar. In both methods, you start by making a dough of the flour and water and mix it for a period of time. While mixing you’re determining just how that dough behaves by measuring the resistance to mixing and how that changes over time.

Flours with very strong gluten, a high protein quality, will require a long force for a long period of time. If you’d make these into a bread, they can withstand long periods of very intensive mixing. Flours with less strong gluten drop in the force required sooner. These proteins cannot be kneaded for as long or as strongly.

To make a good bread out of flour it needs to be able to develop a strong gluten network. Just how strong depends on the bread you’re making.

These methods measure more though than just protein quality. They are also used to determine how much water can be absorbed by the flour and how quickly this happens. This is also of importance for making any type of dough.

Alveograph & Extensograph

These next two pieces of equipment test for a slightly different aspect of the quality of the protein (don’t ask me why all these names are so similar by the way!). Instead of measuring the strength of the protein by kneading it, these methods focus on the stretchability of the gluten.

Again, both methods start by making and mixing a dough according to a set protocol. The alveograph then blows a bubble of a piece of dough. Just how big the bubble can become is a measure for the quality of the gluten. The extensograph on the other hand stretches the dough, as if you’re stretching it between your hands, until it breaks. Both methods indirectly look at the extensibility, elasticity and strength of a flour.

Flour quality

When a miller receives a new batch of grains from a farmer, they’ll execute several of the tests above, but probably not all of them. Actually, different countries and regions will have a preferences for slightly different tests. It will depend on what the farmer and miller have agreed upon in their specifications.

Based on these initial tests the miller will know what type of flour this wheat is best suited for. That might impact their decision on how to mill it, whether they make it into a whole grain or white flour for instance, and of course how to package and sell it. Especially larger manufacturers have the luxury of having large supplies of grain. Therefore, they can blend different wheat supplies to ensure the quality that you buy in a store is always consistent.

Smaller farmers and millers often do not have that luxury. As a result, their flours may still pass the tests, but behave quite different than those standardized flour types! When working with bakeries, they’ll do test batches and the tests above, to ensure their bakers can bake a good bread (or whichever product they want to make). For us individual consumers, we just have to give the flour a try and experiment a little!

References

Classo Innovation, De grondstoffen van brood, link

Ferris Jabr, Bread is Broken, Oct. 29, 2015, link

Meera Kweon, Falling number in wheat – How is it calculated and what does it mean to producers?, 2010, link

Horvati, D., et. al., The Relation between Dough Rheology and Bread Crumb Properties in Winter Wheat, Agriculturae Conspectus Scientificus | Vol. 73 (2008) No. 1 (9-12), link ; worth a read if you’d like to see several of the measures we discussed above in action in a research setting!

Macrina Bakery, The Bread Lab: A Washington State Treasure, June-13, 2016, link

Macrina Bakery, From Seed to Loaf: Growing Your Own Wheat, May-27, 2020, link; Macrina Bakery has grown their own wheat for baking some of their bread!

Rebecca Miller Regan, Flour testing in the quality control laboratory, Miller Magazine, link

Khan, Khalil. Wheat: Chemistry and Technology. United States, Elsevier Science, 2016, link

Washington State University, Frequently asked questions: Low falling number and wheat, link

Wheat Marketing Center, Wheat and Flour Testing Methods, 2004, link

Falling numbers of grains collected by Washington State University over 2013-2019 harvests, link