The Science of Bread (Part 4) - Rye Flour and Rye Bread - References and Details (2024)

Why is rye flour such an underrated flour for making bread? Is it because it lacks the intense gluten network of wheat? Or because people don't like the flavor? Well, maybe the science behind rye flour and rye bread will convince you to try it out in your bread making, because I really think you should!

Here are the link and embedded rye bread science video on YouTube, and below that are my video notes and references I used for the information.

Links to other bread science videos and references

Part 5 - The Science of Salt-Rising Bread: Citations and References ; YouTube Video

Part 4 - Bread Science - Rye Flour and Rye Bread

Intro Slide:

Hello everyone, today I am here with the 4th installment of the bread science video series. I will discuss rye flour, which I often use in bread baking.

While conducting research online for this video I discovered that there is quite a bit of conflicting information on rye flour, especially in terms of rye flour proteins, and also that there is generally less information (available publicly) on rye flour, as opposed to wheat flour. So I definitely feel like there is a lack of clear and consistent descriptions of rye flour, but my hope with this video is to highlight some interesting qualities about rye flour, as well as characteristics that may differentiate it from wheat flour.

Rye flour is popular in certain types of breads and in sourdough bread baking due to it’s influence on the bread’s flavor and it’s contributions to fermentation, so I do highly encourage all of you to experiment with rye if it is available where you live.

Slide 2-Outline

For a visual on the differences between rye and wheat flour during fermentation, check out my sourdough starter feeding video where you’ll see how differently they rise and the different textures of the starters.

The outline for today’s presentation includes defining what rye is, a discussion of different rye flours around the world, characterizing rye and it’s proteins, sugars, and enzyme activity and how that influences bread making, and finally a look at rye in sourdough baking.

Slide 3-What is it?

Rye is a grass (Secale cereale) that is a source of grain. Rye is a member of the Triticeae tribe, along with wheat and barley. Therefore, rye is closely related to both wheat, a member of the genus Triticum) and barley, a member of the genus Hordeum).[1] Rye grains are used to make bread, beer, some whiskeys, and some vodkas. Rye grains can be eaten whole, either as boiled rye berries or by being rolled, similar to rolled oats.[1]

Similar to wheat flour, rye grains contain a endosperm, bran, and germ. Therefore, you can purchase flours with different proportions of these components, for example whole grain rye flour, or fine rye flour.[2]

Slide 4-Rye flours

Now to discuss rye flours, which, as shown in this image, can range from highly refined white rye flour to whole rye grains. Unlike with wheat flour you won’t get similar labels with rye flour.

For example, typically there are no “cake rye flours” or “bread rye flours”. Instead you will often see a differentiation between “light” or “dark” rye flours, or finely ground to coarse ground rye.

However, depending on where you live you may, or may not see this wide variety of rye products. For example, in the U.S. and Canada you’ll often see only one or two rye flours being sold. Typically they are “light” or “dark” rye flours. A light rye flour is similar to an all-purpose flour, usually having most or all of the germ and bran removed[2] (so it’s low in protein and high in starch[3]), while a dark rye flour usually contains the bran and germ as it’s usually made from milling the whole rye grain.[4]

Slide 5-Rye flour in U.S. and Canada

Although there is a large potential range for rye flours as seen in the previous slide, you don’t really see this variety in the U.S. and Canada. Instead in the U.S. and Canada, I’ve almost exclusively seen dark, coarse rye flour in grocery stores like the brands you see here, but other countries can have a greater variety of rye flours.

Slide 6 - German rye flours

An example of a country that has an extensive variety of rye flour is Germany. In Germany, there are 8 common rye flours, most of which can be found in regular markets or supermarkets. So essentially, in Germany they do have that big range of rye flours seen in the picture from a few slides ago, ranging from light to dark and fine to coarsely ground rye.

Slide 7 – Germany classification

To go into more detail about German Rye flours, the rye flour classification is quite specific. The purpose of this slide is to showcase the different types of rye flour commonly sold in Germany, and they are often differentiated based on ash content.

What is ash, or mineral content? It is the amount of ash, or mineral leftover after burning flour. For example, if you burn 100 g of flour and 1 g of material is remaining, the flour is 1% ash. Wholegrain rye flours tend to have a higher ash content because the bran, germ, and outer endosperm contain more minerals, so the more wholegrain the flour is, the more ash you will get.

These different rye flours have different uses in baking, as shown in the right-most column.

Slide 8 - Places where it’s grown (map):

So why would Germany have such a vested interest in Rye flour classification? Well, this is because rye flour is extremely popular in Eastern and Northern Europe.

Rye can grow better in colder climates than certain grains.[1] As you can see in these maps, the areas in which rye is grown in both has to do with climate and Rye usage. Rye is very popular in eastern and Northern European breadmaking it is typically exported from Germany and Poland.[1]

Slide 9 - Why is it popular in eastern and northern European baking?

Outside of it’s cultivation areas, there are also longstanding traditions of baking mixed rye bread or 100% rye breads, which can be extremely flavorful[2] and last a long time, especially when fermented prior to baking. These countries in Europe aren’t the only countries that use rye flour, but rye is very popular here!

Slide 10 – Rye characterization

Now I am moving onto the rye characterization section of this presentation.

If you’ve ever worked with rye flour you’re probably thinking that it sounds crazy to make a bread that’s 100% rye because it’s such a sticky dough that acts more like a batter than a wheat dough which tends to be firm and elastic.

So I will discuss why rye is so dang sticky. There are three major reasons, and I will discuss each one in depth in future slides. The first is the gluten proteins, as well as the sugars and amylase enzymes present in rye.

Slide 11 – Gluten: one of many proteins in flour

Gluten, as mentioned in my previous bread science videos, is often thought to be mainly comprised of glutenin and gliadin that, when hydrated, form gluten.

Play animation. However, different cereal grains contain different kinds of proteins. Gluten can be considered a “storage protein”.

So when we consider rye, Rye grains contain a lot of secalin, which is another form of storage protein like gluten. Secalins are similar in structure, or function to glutenin and gliadin (Pasquali et al. 2019; 'Catcher of the Rye: Detection of Rye, a Gluten-Containing Grain, by LC-MS/MS'), but lack that cohesiveness and elasticity that can help build bread structure in wheat breads.[7]

Play animation. However, along with secalin, rye may also contain glutenin and gliadin.

Play animation. However, the proteins in rye are debated. Some sources I found state that rye only contains secalin, while other say it has secalin and gliadin, but no glutenin[3]. Furthermore, some sources state that there is a little glutenin in rye flour but much more gliadin. What I have also found that may clarify this issue is that both gluten and secalin may contain protein fractions called gliadin[13], so if both secalin and gluten have gliadin but they aren’t well differentiated than perhaps this explains the confusion.

Slide 12 – Rye proteins

My thoughts are that…

If you have a clear answer to this issue and know more about rye proteins, please feel free to discuss this in the comments and provide clarity!

One source I found explained that although dark rye flours can have a gluten content as high as 16%, this is primarily gliadin[3]. Essentially, if Rye flour is high in gliadin but low in glutenin. It therefore has a lower gluten content than wheat flour. Glutenin on it’s own provides strength and elasticity while gliadin contributes to viscosity, cohesiveness, and extensibility (Biesiekierski, 2017: https://onlinelibrary.wiley.com/doi/10.1111/jgh.13703). Gliadin is water-insoluble while glutenin is water soluble.[9] Therefore, when gliadin is hydrated it acts like a viscous liquid that imparts extensibility.[10] and makes the dough sticky.

The fact that there is more gliadin means it will be sticky and extensible, but not strong. Therefore rye doughs can struggle to hold the gas produced by the yeast during fermentation.[3] This can result in a small and compact loaf of bread made primarily from rye flour.[3]

Slide 13 – Sugars and starch in rye

Rye contains more sugars[2] than wheat flour. Surprised? Rye flour contains more free sugars than wheat flour, which can enhance fermentation[2]. There are important complex sugars in rye flour called pentosans, which are particularly high in Rye although they are present in other flours. For example, wheat flours and in particular whole wheat flour and wheat bran also contain a lot of pentosans.[11]

These pentosan sugars compete with rye proteins for water[2], i.e. meaning that the pentosans are hydroscopic.

When pentosans break apart during mixing and fermentation, this makes the dough stickier.[2] Therefore, it’s not just the rye proteins that makes dough sticky!

There is a difference between water soluble and insoluble pentosans.

Slide 14 – Amylase in Rye

To reference back to the first bread science video, this is an example of an enzymatic chain during wheat dough fermentation, where we have enzymes like amylase, maltase, zymase, and invertase breaking down sugars.

Rye flour contains a lot of amylase, which is that enzyme that breaks down the starch in rye into simpler sugars like maltose and glucose. Refer to my first bread science video to learn more about that.

Therefore, when hydrating rye flour and during fermentation the breakdown of too much starch in a rye dough can result in the dough becoming gummy and losing some structure.[2] So amylases are yet another reason why rye doughs can be sticky.

However, remember that enzymes operate best at a preferred temperature and pH. And amylases tend to slow down at a low, or acidic pH. Therefore, an acidic sourdough environment can slow down the amylase activity and slow down that starch breakdown.[2] Therefore, incorporating rye in sourdough bread baking can actually improve the quality of the resultant rye bread![2]

Slide 15 - Why rye breads usually need to rest before cutting:

If you cut into a bread with a high % of rye flour too early, it may be gummy and have an unpleasant texture. Therefore, recipes often recommend letting it rest 1-2 days so the crumb can set up[2] and moisture can distribute within the bread.

The recommendation: >60% rye rest 24 hours before cutting into. 100% rye should rest 48-72 hours before cutting into.[12]

Furthermore, the flavor of rye bread can improve with time, which may be another good reason to let it rest.

Slide 16 - Using rye in bread baking and why I love rye:

Rye can be used in various quantities. For example, it can be used as 5-15% of the flour and contribute to the overall flavor of the bread without affecting the structure too much.[2] Conversely, It can be used at 100% and significantly affect the flavor and structure.

Here I show two fast-fermentation mixed rye breads followed by a slow fermentation rye bread. I love all ranges of rye bread, from light rye breads to dark rye breads. On the higher end with 70-100% rye breads the dough is very sticky and is more like a thick batter that you don’t knead and instead smoosh it into the loaf pan to bake. The 70% rye bread here with lots of seeds and nuts was fermented for several days, giving it a tangy alcoholic flavor. Certainly a very robust brick-like loaf.

In my sourdough baking I love using my rye sourdough starter in my sourdough loaves because I’ve noticed that I get a more pronounced sourdough flavor from my rye starter instead of my wheat starter, even though breads made with my rye starter tend to rise more slowly.

Slide 17 – Rye in Sourdough baking

So let’s explore rye in sourdough:

One factor that does influence the structure of rye breads is the fermentation process, especially with sourdough, which can trigger acidification that can cause rye proteins (secalin) to swell and hold water, which can help the bread maintain structure.[7]

AS mentioned, pentosans and amylase influence bread structure and starch breakdown in rye bread doughs.

These pentosans can also attract yeast[5] and sourdough bacteria[8], which can help to build a strong sourdough starter community. Rye doughs are also rich in amylase, which can enhance sugar breakdown providing more sugar for these sourdough yeast and bacteria communities. Therefore, rye flour can speed up fermentation[5].

Some research also indicates that the amylase in rye flour is different from amylase in wheat flour and may be better able to survive the baking process[5] This can be slightly problematic because prolonged amylase activity can destroy more starch and negatively affect the bread’s structure. However, the fermentation and enhanced starch breakdown can be slowed down if something were to inhibit that amylase. So at low pH in sourdough fermentation, the amylase is somewhat inhibited, which can help prevent overfermentation[6].

As mentioned, rye has a different, and sometimes preferred flavor over wheat flour. Often people consider it to taste sour[5], which enhances the sour in sourdough.

Using sourdough to ferment rye bread can result in a slightly less dense product.[5]

Rye flour can be considered more nutritious than wheat flour, for example it has more soluble fiber and a complete amino acid profile, but I will not go into the health details in detail.[5]

As mentioned, the ability of rye flour to slow staling can improve the sourdough bread’s longevity, similar to wheat sourdough breads.[7]

Slide 18 - Summary:

References / Citations: