An introduction to bread and the science of how flour, water, salt, and yeast play a role in the formation of delicious bubbly fermented bread! The video is long, and the audio has some issues, and if you would like more information, or an easier to read version of the info in the video, look below. The references are referenced in [brackets] and the links are a the bottom of the page.
The Video (adjust the bar to start at the beginning)
Feel free to check out the other bread science videos and information:
Part 2 - The Bread Making Process: Citations and References ; YouTube video
Part 3 - The Science of Sourdough Bread: Citations and References ; YouTube Video
Part 4 - The Science of Rye Flour and Rye Bread: Citations and References ; YouTube Video
Part 5 - The Science of Salt-Rising Bread: Citations and References ; YouTube Video
Part 1: Flour Water Yeast Salt
Slide 1: Title Slide
Slide 2: Introducing
Slide 3: Outline
Slide 4: Flour Outline
Slide 5: The Grain Itself
The grain itself
The wheat grain contains everything the little baby seed needs to start growing into a plant (to germinate). For example, it contains carbohydrates (mostly starch), proteins, and fat. The grain also contains the enzymes that help breakdown and metabolize these materials during growth.[9]
Vitamins and minerals are found in flour, especially whole grain, including: Selenium, Manganese, Phosphorus, Copper, and Folate (a B vitamin).[17]
Slide 6: Milling
100 g whole grain wheat flour[17]:
· Calories: 340
· Water: 11%
· Protein: 13.2 grams
· Carbs: 72 grams
· Sugar: 0.4 grams
· Fiber: 10.7 grams
· Fat: 2.5 grams
Slide 7: Milling
Milling
Millers can choose to make a whole-grain flour, which uses the whole grain (the bran, the germ and the endosperm) or make a white flour, which uses the endosperm only (the bran and germ are sieved leaving the endosperm).[16] Some “white” flours are subsequently enriched with vitamins after milling to try and fortify it, the vitamins can include iron, thiamine, niacin, calcium, Vitamin B6 etc.[17]
Whole wheat flours tend to contain the most protein, but do not form gluten as well as bread flour or all purpose flours because the shards of germ and bran break gluten strands.[27]
Slide 8: Starch
Starch
Starch makes up roughly 70% of wheat flour by weight. It helps form gluten and absorbs water during baking (gelatinizes), which also helps traps CO2 and create the bread’s structure.[3] Starch is also the source of most of the bread’s flavor.
Slide 9: Protein
4. Protein
Flour in the U.S.A. usually contains between 10-15% protein[1] whereas in Canada it is about 13-16% protein[5]
b. Gluten
The molecules that form gluten are typically found in the seed’s endosperm.[16]
Glutenin and gliadin are proteins that bind together with the help of water to form gluten (also a protein).
Slide 10-11: Gluten
The gluten that forms (from the binding of glutenin and gliadin via water) is stretched and strengthened through the kneading process, becoming strong and elastic (like a stretch rubber band), and building the structure of the bread.
During that strengthening process the gluten strands bunch up, but then with time the gluten strands hydrate and relax, loosening up.[16] When the gluten is relaxed and the flour is hydrated, the gluten is less likely to bounce back when stretched.
Kneading stretches and strengthens the dough proteins. Relaxing hydrates and helps relax the proteins, making them stretchier.[16]
Slide 12: Gluten and time
Gluten doesn’t only develop with kneading, it also develops with time. For example, a no-knead bread can take anywhere from 12-24 hours to ferment. Afterward, when you dump it out there’s stretchy gluten strands. How??? The longer hydration time allows more gluten bonds to form, and more enzymatic activity improves gluten formation.[21]
Another gluten developing factor is the yeast you add to the dough. The yeast essentially develops gluten microscopically. First, the enzymes in the flour and yeast can break down the gluten proteins into smaller pieces overtime, which can more easily form a gluten network. Secondly, The CO2 released during fermentation gently moves and rearranges the proteins in the dough, thus rearranging and building the gluten network.[18] So imagine millions of teeny tiny yeasts kneading the dough instead of you.[20]
Slide 13: Gluten and Flours
Not all flours have the same gluten. E.g. within wheat flours a bread flour has high gluten, followed by AP flour with intermediate gluten, and cake flour with low gluten.
And then if we think about different grains for example, rye and teff flour have very low gluten.
And if we go deeper into whole grain flours things get even more wild, but we won’t do that for the sake of this video.
Slide 14-15: Images - Gluten
Slide 16: Enzymes
5. Enzymes
What are enzymes? They’re everywhere, in our bodies, in food, in the soil, water, plants, they are just everywhere. Enzymes are proteins that speed up biological reactions. For example, they can split apart proteins, fats, and carbohydrates (sugars).[6,9]
Bacteria and yeast can produce enzymes to facilitate reactions that are beneficial to them, for example. They bind to a molecule (substrate), and can speed up the rate of a reaction, that reaction being the breaking up of a molecule (the substrate) or putting molecules together. These enzymes can theoretically work forever as long as conditions are ideal. Enzymes are very sensitive to pH and temperature, as well as the concentration of the substrate.
Slide 17: Enzyme Sensitivity
Temperature, pH, and availability of a substrate. Many enzymes grow within a certain temperature and pH range (show graphs). The peak of these are the optimum temperature and pH. I won’t get into pH much, but I will go into temperature.
Temperature wise, think about molecules moving around faster when it’s warm, and not moving around as much when it’s cold. So, when it’s cold, the enzyme has less of a chance of bumping into and binding with the substrate. But in warmer temperatures there is more heat energy that increases the chance that the enzyme will bounce into and interact with the substrate. So, the rate of the reaction typically increases with temperature, to a point.[19]
At too high of temperatures the bonds within the enzyme start to break down (this is called denaturing), and/or change shape of the binding site, which doesn’t allow them to bind with the substrate anymore, rendering them ineffective.[19]
Concentration of substrate: Obviously, the amount of substrate also influences enzyme activity and the rate of the reaction. This may be a no-brainer, but you can think of it as a resource balance, because enzymes will eventually use up, or convert all the resources available if they are not restricted.
Slide 19: Enzymes
It’s weird to think about, but bread doesn’t technically need added sugar. Instead the flour contains sugar, but that sugar is usually tied up (bound within) in starch.[9]. Starch is essentially a large polymer carbohydrate made up of a complex Carbon structure, and starch can be broken down into simpler sugars (carbohydrates) that can be extracted by enzymes.
Slide 20: Amylase
Amylase is an enzyme that breaks down sugars. It’s in our saliva, for example, and helps us break down and digest food.[7]
Amylase Is also in flour[9] and yeast. In bread it breaks down starch into maltose, a simpler carbohydrate.
Slide 21: Maltase
Maltase is another enzyme in yeast. Maltase can break down maltose (essentially 2 glucose molecules bound together) into glucose.
Yeast then metabolize glucose into CO2 and ethanol.[1] In fact, 1 molecule of glucose yields 2 CO2 and 2 molecules of ethanol.[4]
Slide 22: Invertase
So clearly amylase is the start of this very important chain of reactions. However, it takes TIME for the amylase in yeast to break down the starches in flour.[7] This is why bakers often add sugar to commercial yeasted bread in order to speed up the process.
Normal white sugar in the US and Canada is Sucrose, which is a disaccharide that consists of 50% glucose and 50% fructose[8]. So there you have it, a shortcut! Instead of waiting around for enzymes to activate to produce glucose, you already have it in the dough if you add sugar!
In fact, commercial yeast can contain another enzyme, invertase (S. cerevisiae have this), which can break down sucrose into its components: glucose and fructose, making fermentation even more efficient.[9]
Conversely (to commercial yeasted breads), sourdough relies on that long chain of reactions.
Slide 23: Proteases and Lipases
Overproving: If the yeast run out of sugars to eat, they start eating the protein, i.e. the gluten[6], which starts to interfere with bread structure. This is one of the reasons why overproving is bad.
Proteases: Flour and yeast contains proteases.[9] These break down protein (i.e. gluten) in the bread[6] into amino acids, which can improve the bread’s flavor[18]. This breakdown helps with elasticity to a degree, but too much protease activity can harm the bread’s structure by breaking down gluten.
However, bread usually does not contain a lot of protease enzymes.[6] Therefore, there is usually a natural balance of protease activity in bread, where proteases break down the protein a little to make the bread softer and more workable, but not so much that it destroys the gluten.[9] So avoid overproving!
Fat: broken down by lipases. Fat makes up ~2-3 of most whole grain wheat flours.[17]
Slide 24: Flavor
Flavor
Slide 25: Yeast
Single celled microorganisms (fungi)
We will discuss baker’s yeast for this discussion: baker's yeast is primarily made with Saccharomyces cerevisiae species[5]
Contain enzymes
Slide 26-27: Fermentation
Yeast perform fermentation, where they consume sugar in starch or added sugar in the dough. Yeast break glucose into ethanol and CO2 in the process of fermentation.
Fermentation is anaerobic (occurs without oxygen)[16]
It’s a way for microbes (yeast in this case) to get energy when there is very little to no oxygen, so fermentation kicks in to utilize energy (glucose) anaerobically.[18]
Slide 28: Baker’s yeast
Fresh yeast: not really a thing in the U.S.A. and Canada, more popular in Europe
Active Dry and instant yeast: Yeast cells are dormant (sleeping), and they’re dried out. They are reactivated with warmth and food (sugar usually).
Active dry yeast: Larger granules, you need to dissolve in water, with or without sugar[12] (at 38°C or ~100°F) to activate them, which also takes a little time[5]
Instant yeast: smaller granules, can mix right into the flour and will activate.[12]
There’s also Rapid-rise instant yeast: also in small granules but is usually also made with added enzymes and other additives, so it is meant to be used for doughs you want to shape and bake right after kneading.[12]
Slide 29: Yeast sensitivities
Enzymes are activated and influenced by water, temperature changes, and pH
For example, the ideal temperature for amylase activity is 104–140°F (40–60°C), and an optimal pH range of 5.5-6[11], which also happens to be near the range of temperatures that yeast is most active (~80-110°F). Above 140°F and you’ll kill yeast.
Maltase also has a temperature range, with 118-122F (48-50C) being it’s optimum, and pH range 5-7.[15]
Invertase is more active at temperatures between 104–140°F (40 and 60°C) and pH ranging from 3 to 5.[14]
Yeast itself, i.e. the fermentation process, occurs best at 90-95°F (32-35°C). Every degree above or below this can depress fermentation relative to this range.
In addition, too high of temperatures can limit fermentation (ethanol production) and make the yeast more sensitive to the harmful effects of things such as lactic acid, and to high levels of its own ethanol that’s built up.[13]
Yeast and enzymes also have pH preferences
As the sugars break down during long dough fermentation, and as the yeast release CO2, organic acids, and the ethanol generates acid (acetic or lactic acid), the dough’s pH begins to drop.[18]
So not only are the resources beginning to decrease, but the pH is lowering to ranges where the enzymes are less active. As such, dough with an extreme pH can start to deflate as the yeast run out of food and ideal growing conditions. Overproving can cause this.
Slide 30: Cold ferment
Yeast uses ANOTHER enzyme in fermentation, and that is zymase. As with any enzyme, its activity is affected by temperature. Which is why bread will rise slower in a refrigerator as opposed to a warm room.
Some believe a long, cold ferment enhances flavor, and it might, because it might allow certain enzymes to remain active for longer, developing flavor. And the science behind this is that a cold ferment reduces yeast and their associated enzymatic activity. However, the bacteria that are likely in your dough remain quite active at cold temperatures, and can produce more acid that enhances the bread’s flavor.[18]
Flavor
Slide 31: Water
Water plays a role in gluten formation, enzyme activity, dough extensibility
I mentioned how water helps glutenin and gliadin interact to form gluten, the main structural strength component of bread.
Water helps with enzyme activity because it allows enzymes to move around and catalyze reactions, in addition to being part of some reactions as a reacting molecule (I think…)[9]
Water hydrates the starches, helping with bread structure
Water helps dissolve flour and yeast so they mix thoroughly[5], which helps the enzymes activate and access more substrates.
When water vaporizes during baking, this contributes to gas production during baking, forming bubbles.
Slide 32: Salt
Salt plays a role in gluten formation
Although the gluten proteins naturally repel one another, the chloride ions (Cl-) in salt help them overcome that repulsion and stick together. Therefore, salt helps form the gluten network and strengthen the dough.[21]
Salt influences enzyme activity, including protease activity [6]
Too much salt can kill yeast, because it can create osmotic stress
Salt influences the flavor of the bread and improves crust color[5] (browning) because it slightly hinders fermentation, allowing more sugars to build up (that will participate in the Maillard reaction). Bread can be bland without salt.
Salt acts as a preservative, driving away certain microbes and molds
References:
1: Compound Chem: https://www.compoundchem.com/2016/01/13/bread/
2: Stella Culinary: https://stellaculinary.com/audio-podcasts/stella-culinary-school/scs-019-twelve-steps-bread-baking
3: Exploratorium: https://www.exploratorium.edu/cooking/bread/bread_science.html
5: The science of bread making: http://www.thescienceofbreadmaking.com/yeast.html
6: The Bread Maiden: https://thebreadmaiden.com/2016/06/22/the-science-behind-enzymes/
7: Wikipedia: https://en.wikipedia.org/wiki/Amylase
8: The health line: https://www.healthline.com/nutrition/sucrose-glucose-fructose#what-are-they?
9: Scientific American: https://blogs.scientificamerican.com/guest-blog/enzymes-the-little-molecules-that-bake-bread/
10: Modernist Cuisine: https://modernistcuisine.com/2018/09/sourdough-science/
11: Bakerpedia: https://bakerpedia.com/ingredients/amylase/
12: The Kitchn: https://www.thekitchn.com/whats-the-difference-between-active-dry-yeast-and-instant-yeast-54252
13: Lallemands: https://www.lallemandbds.com/wp-content/uploads/2013/06/LBDSMascoma_ThermostabilityDocument.pdf
14: Science Direct: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/invertase
15: Mcwethy and Hartman, 1979: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC243360/
16: GRDC: https://grdc.com.au/__data/assets/pdf_file/0027/227745/grdc-science-behind-dough-fa.pdf.pdf
17: Healthline: https://www.healthline.com/nutrition/foods/wheat#nutrition
18: Fine cooking: https://www.finecooking.com/article/yeasts-crucial-roles-in-breadbaking
20: The kitchn: https://www.thekitchn.com/the-science-behind-yeast-and-how-it-makes-bread-rise-226483
Wang et al. 2015: https://ift.onlinelibrary.wiley.com/doi/abs/10.1111/1541-4337.12143
26: The Spruce Eats: https://www.thespruceeats.com/what-is-gluten-995123
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