What Is The Role Of Soy Flour In Baking Bread?

Soy flour is used in bread making
Published on
05 September 2021
Gareth Busby
Gareth Busby

Soy flour isn’t a new thing in the baking industry. It’s widely used in many baked goods to not only boost nutritional value, but also to improve texture, moisture, and shelf-life. Soy flour is very high in protein, so bakers use it alongside wheat flour to improve the quality of their bread. This article explains what soy flour is and how soy flavour improves bread dough.

What is soy flour?

Soy flour is made by roasting soybeans. They are then dehulled and ground into a fine powder. This flour is used to add high-quality protein, because of its high lysine content. It also adds a slightly nutty flavour and acts as a natural dough enhancer. There are two types of soy flour that are available in the market: full-fat and defatted:

Full-fat, also known as natural soy flour, contains the natural oils that are found in whole soybeans.

Defatted soy flour has had the oils removed during its production process.

Both types are great sources of high-quality protein, however defatted soy flour is more concentrated. Since the natural oil content of fatted soy flour can have a considerable impact on moisture, shelf life, and texture of baked goods; food manufacturers usually prefer to use defatted soy flour in their products. For this article, we will concentrate on using the defatted version.

How does soy flour improve bread?

The main function of using soy flour in bread dough is to increase its protein content. Soy flour is approximately 50% protein, which is a lot more than the wheat flour used to make bread. The protein content of bread flour varies from 9-14%. The inclusion of soy flour enhances the machinability of the dough and improves the texture of the bread. It also adds a slightly nutty flavour. Other benefits are:

Provides emulsification to the dough

Soy flour contains lecithin which acts as an emulsifier. It thickens batters and doughs, to provide a stronger mixture.

Lowers costs through increased water absorption

The high quantity of soy proteins increases the amount of water that can be absorbed in a dough. This has a couple of benefits for professional bakers, most notably cost control.

You are able to exchange bread flour with half the amount of soy flour whilst keeping the rest of the ingredients the same. As soy flour is cheap, its use lowers the production costs of the bread.

Improves shelf-life

The extra water that’s absorbed also delays the staling process. It does this by slowing the retrogradation of the starch.

Provides strength whilst lowering the gluten content of the bread

Unlike the proteins flour in wheat flour, the moist soy proteins do not turn into gluten. It means that soy flour can be gluten-free so is often found in gluten-free flour mixes. Further processing is required to make soy flour gluten-free.

Its inclusion in bread dough not only increases the amount of protein but improves protein efficiency. An experiment called, enrichment of bread with soy flour, conducted by “E Yáñez, D Ballester, M Aguayo, H Wulf” shows that the protein efficiency ratio of bread improved from 1.17 to 2.13 with the inclusion of 6% soy flour.

Increases browning on the crust

Due to the increased protein, the Malliard effect is more effective. This causes the bread to brown faster in the oven. If using soy flour, you can lower the heat and lengthen the baking time to compensate.

Lowers fat absorption

Dough that includes 3-3.5% soy flour resists fat when fried. It’s a great inclusion for fried bread products such as doughnuts. 

Produces further rising through foaming

Lecithin, also found in egg yolks creates foaming when heated. This offers a small increase in the rise of the dough as it traps more CO2.

Increases swelling of the bread

Soy flour does produce swelling once baked. When levels of over 4% are used this will have a negative effect on the bread. The use of sodium stearoyl-2-lactylate (SSL) can correct the shrinking somewhat. At the levels of 10 and above, SSL was not effective in preventing the decrease in size.

Adds oxygen to the dough

The enzyme lipoxygenase, which is present in soy flour, is a popular oxidizing agent used in bead manufacturing. It enhances the gluten structure to strengthen the dough whilst providing oxygen for the yeast respiration process. This benefits quickly-made bread, but lipoxygenase can also lead to over-oxygenation of the flour and bleaching of the xanthophyll pigments.

Overuse will lead to the bread collapsing but in light use, the crumb will become whiter and some of the “bready flavour” is lost.

Improves dough handling, sheeting quality and lowers fermentation time

Because of a combination of the effects described above, the dough becomes stronger and ferments faster. This means the dough does not need to be fermented as long as it would otherwise. It holds its shape when handled or passed through machines better and provides stronger layers when creating pastries such as croissants or Danish pastries.

How much soy flour should I use per loaf?

As you can see, soy flour does a little bit of emulsification, improves the bonds via its protein content, adds colour and helps to keep bread fresh. It isn’t an enzyme that improves one issue, soy flour does multiple! But there is a limit to how much can be added. Soy flour shouldn’t replace all of the wheat flour in bread. Levels of over 8% can produce a stickiness in the dough that make handling difficult.

Recalling the tests conducted by E Yáñez, D Ballester, M Aguayo, H Wulf, they tested the effect of soy flour in dough in ranges of 2-15%. With higher inclusions, the bread deteriorated. It’s best to use less than 8% in bread dough.

Depending on what you are looking to achieve, 2-5% soy flour to the amount of wheat flour used is best.

Using soy flour as an egg replacement

Soy flour, especially soy flour that’s been lechithinated, is used as a cheap alternative to dairy products. It enhances the dough without the risk of lactose intolerance, and milk allergy and also makes the product vegan friendly. This ingredient contains calcium and vitamin A, which are essential for bone health and eye development.

Yet soy flour can only replace part of the properties of an egg. They are much more complicated than this. Therefore it should be used in conjunction with other enhancers. 

Soy flour is made for soybeans

Are soy flour and soy lecithin the same?

Even though soy flour and soy lecithin both come from soy, they have differences. First is the process of making it. As mentioned earlier, soy flour comes from finely grinding soybeans. While soy lecithin comes from the process of making other soy-based products like oil, tofu, and milk. It is the waste product left during these processes.

Soy lecithin is added to soy flour to produce soy flour that’s lechitinated. It’s often used to coat the flour to make pellets.

Soy lecithin is a collection of several phospholipids that have both health and industrial uses. It’s usually used as an emulsifying agent or lubricant when added to food. It also contains antioxidants and other properties that protect flavour.

Soy flour nutrition

Despite having almost 50% protein content, soy flour doesn’t produce gluten. So it’s great for gluten-free diets. Since it comes from plants, it’s also cholesterol-free and low in saturated fats. Besides that, it also contains a good balance of amino acids, which are important to maintain good overall health.

Listed on the table below are its nutrition details:

Nutrients per 1 cup of defatted soy flour

Protein (g)47.01
Total lipid (fat) (g)1.22
Carbohydrates (g)38.37
Energy (kcal)330
Sugars, total (g)20
Fibre, total dietary (g)17.5
Calcium, Ca (mg)241
Iron, Fe (mg)9.24
Magnesium, Mg (mg)290
Phosphorus, P (mg)674
Potassium, K (mg)2384
Vitamin A, IU 40
Sodium, Na (mg)20

What can I use as a substitute for soy flour?

The only ‘problem’ with soy flour is that the trypsin inhibitor is not removed during its process. This is common with most legumes and some people claim that it makes digestion harder. Besides that, it’s still a great addition to a gluten-free, vegan, or low-carb diet. But if soy flour is hard to get in your area or you just want a different substitute, you might want to consider these:

  • Chickpea flour: another gluten-free ingredient that can also provide a tender texture and nutty taste. It can also be used in bread, muffins, or crackers.
  • Pea flour: It can give a neutral colour with a mild flavour. It’s also good for holding down the water absorption of the dough. This will work well with bagels, burger buns, doughnuts, and other baked goods.
  • Sorghum flour: another gluten-free ingredient that will work great in making pasta, semi-leavened bread, and flatbread.
  • Lentil and lupin flours: Similar to the others, these flours also have more protein content compared to regular wheat or AP flour. These will also work well in making biscuits, cookies, and other desserts.

Is soy flour always gluten-free?

Soy flour is naturally gluten-free, however, it can be grown in a crop rotation pattern with wheat crops. This means there is potential for wheat to enter the production process. The same machinery used to cultivate wheat fields is also likely to be used to harvest the soybeans. Again, it is possible that wheat gluten could contaminate the soy, making it not totally gluten-free. 

Is soy flour bad for you?

While many people believe that it carries potential health dangers, there’s no concrete evidence that can back this up yet. The tests that you might have heard of were made on animals who ate soy continuously for 5 years. Whether consuming small amounts produces health problems in humans is unknown, but generally unexpected. In fact, it’s present in several products like margarine, and ice cream. So you may be consuming soy without realizing it.

Where can I get soy flour?

Soy flour can be found in most grocery stores and health food shops. However, it’s always best to choose the freshest product available to ensure optimum quality. It’s also important to check the expiration date for guaranteed freshness. In case you can’t find soy flour in your area, you can also buy it online. Some big brands have their own websites, while most of them can also be found on Amazon.

You may see a PDI rating on the packaging of soy flour. This is the amount of water it absorbs. For bread, a high PDI is preferred, this is around 70 PDI. For dry bread and cakes such as crackers and cookies, a low rating is preferred, around 20 PDI.

How to use soy flour in bread at home

If you wish to use soy flour at home to see if it enhances your bread, upon opening a pack or bag of soy flour, you may want to stir it. This is to give you a more accurate measurement if you are not using scales (not recommended!). The soy flour can be added to any bread recipe with the dry ingredients and kneaded. As soy flour absorbs a lot of water you will need to increase the hydration of your recipe. For 1 part of soy flour, add 1½ of extra water to the dough recipe.

You might want to toast your soy flour before using it in your recipe. This enhances the nutty flavour profile further. You can do this by putting your flour in a dry pan over medium heat and stirring occasionally.

Both defatted and full-fat soy flour should be stored in the refrigerator or freezer.

Soy flours can improve the quality of commercially prepared bread. Using it with bread such as French, Italian, wheat, and other types, can enhance the texture and volume of the finished products. 

Frequently asked questions about soy flour

Other sources:

https://www.sciencedirect.com/topics/food-science/soy-flour

https://pubmed.ncbi.nlm.nih.gov/6891578/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5502044/

https://www.bakeryandsnacks.com/Article/2018/04/12/Soya-flour-offers-bakers-the-protein-boost-to-capitalize-on-growing-tend

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