The use of yeast in bread production began 6,000 years ago. Yeast, a word that originally meant the froth of the leavening solution, was not known until 160 years ago, when the microbiologist Pasteur began to understand the microorganism and how it was used to leaven bread. If the fermentation of bread is as fantastic as magic, then yeast is the magician behind it.
So to get to grips with the art of bread fermentation, you should start by understanding this magical micro-organism, which we will unravel step by step below.
First Acquaintance with Yeast
Yeast is by its very nature a single-celled fungus, and you should know that it is alive.
Since it is alive, this means that it reproduces just like we humans do.
Its main food is glucose, and by breaking down glucose it can produce alcohol and carbon dioxide. In other words, alcohol and carbon dioxide are actually excrement from the yeast. But you don’t have to feel disgusted, because this excrement is much healthier than all the junk food that humans produce.
Yeast can be divided into natural and artificial yeast according to the way it is obtained.
Natural yeasts, also known as brewer’s yeast, are widely found in nature in the air, grains and fruit. We can usually extract some of the original yeast from the soaking liquor of grains and fruits and then provide them with nutrients and a suitable environment for growth, and they will multiply by sprouting.
When the density of the yeast per unit volume provides us with sufficient fermentation capacity, it is ready to be taken out to make bread. The natural yeast breads that are all the rage on the market are made using yeast from grains and fruits, which are fully cultured to form a liquid species. The distinctive flavour of this bread is the result of the full fermentation of natural yeast and its partners (other microorganisms such as acetic acid bacteria and lactic acid bacteria).
Artificial yeast is also known as brewer’s yeast and as the name implies this yeast is artificially grown for bread and wine making. Artificial yeast can be classified according to its form as fresh yeast, dry yeast, high active dry yeast (also known as fast yeast powder, instant yeast, etc.)
Fresh yeast is pressed from common live yeast and contains a high level of water. 1 gram of fresh yeast contains 10-20 billion yeast cells.
It is characterised by its ability to tolerate high osmotic pressure and cold, meaning that it can be used in doughs with high sugar levels and is suitable for use in frozen doughs. The shelf life of fresh yeast is short and the storage conditions are demanding, as it has to be kept sealed and refrigerated, so there are many inconveniences in using this yeast for bread making in the general household.
Dried yeast is fresh yeast that has been dried and compressed, and it can be used in as little as one half the amount of fresh yeast. Because the dry environment makes the yeast go dormant, it can be kept sealed for over a year.
Before use it should be activated in warm water at around 40°C before adding to the dough.
Highly active dry yeast is the best variety of yeast colony that has been selected by hand for its high activity and fermentability. It does not need to be activated in advance with warm water and can be added directly to the flour to form a dough, using a third of the amount of fresh yeast.
Highly active yeast is not as resistant to osmotic pressure and low temperatures as fresh yeast, and its use in high sugar doughs can affect the speed of fermentation. However, it is fortunate that high sugar tolerant varieties have been bred out of the highly active yeast, as if the creatures had evolved from generation to generation, and the yeast that have survived are those that are superior in every respect. Highly active dry yeasts, both high and low sugar tolerant, are now our first choice for bread making.
When the baking percentage of caster sugar in the dough exceeds 8%, we should use a high sugar tolerant yeast.
Regardless of the type of yeast, it should be kept sealed and refrigerated in order to keep them as active as possible.
The essence of bread fermentation is that yeast consumes glucose and produces alcohol and carbon dioxide to be released to the outside.
The yeast breaks down 1 molecule of glucose into 2 molecules of alcohol and 2 molecules of carbon dioxide, while also producing some water and heat. There are two prerequisites for bread to expand and become bigger, one is that the yeast produces enough carbon dioxide and the other is that the gluten tissue of the dough envelops the gas and prevents it from escaping.
For example, to make a balloon big and round, in addition to filling it with enough gas, you must also make sure that the skin is strong enough.
For yeast to produce enough carbon dioxide, it has to be provided with sufficient nutrients. Yeast reproduces in the presence of sufficient oxygen and ferments in the absence of oxygen, i.e. it breaks down glucose. These two activities take place simultaneously throughout the fermentation of bread. So in what form does yeast obtain glucose?
Yeast obtains glucose in two ways
1. by the amylase enzyme in the flour which breaks down the starch into maltose. The yeast itself has a maltase enzyme which breaks down the maltose into glucose, which is then available for its own use
2. the sucrose we add to the dough, the yeast possesses a conversion enzyme that breaks down the sucrose into glucose, which is then available for consumption.
If we are making a simple bread with no sugar, then the only way for the yeast to obtain glucose is the first way and the fermentation will then take longer; if we are making a nutritious bread with added sugar, then the yeast can obtain glucose in both ways and the fermentation will naturally be faster (provided that a high sugar tolerant yeast is used).
The fermentation of the dough promotes the formation of gluten, and a strong gluten is what keeps the fermentation going (carbon dioxide), so good kneading and fermentation techniques are essential for good bread.
Understanding the principles of yeast fermentation plays an important role in mastering bread fermentation techniques.
Now we come back to bread making. Bread making can be divided into direct and indirect methods according to the method of fermentation.
In the direct method, the flour and yeast are kneaded directly into a dough without any seed dough, then primary and secondary fermentation takes place and the dough is finally baked in the oven.
In contrast, the indirect method involves making a seed dough and fermenting it fully, then adding the remaining ingredients and kneading it into a dough for primary and secondary fermentation. Due to the long fermentation time, the bread is better able to release the flavour of the grains and the flavouring substances produced by the fermentation.
Factors Affecting the Rate of Fermentation
We know that the time and circumstances for fermentation are different for different types of bread. Some breads require a long fermentation at low temperatures, while others are ready in a few hours at room temperature.
What affects the speed of fermentation of yeast?
- The amount of yeast
It’s a very simple fact that the more yeast that is involved in the fermentation of the dough, the more gas will be produced by the breakdown of glucose. But more yeast is not better, just as you can’t grow crops intensively. Too much yeast will compete for what little resources are available in the dough, resulting in some of the yeast being unpalatable, which will also affect the speed of fermentation.
- Dough temperature
Temperature is a key factor in the speed of yeast fermentation. Yeast grows best at temperatures between 25 and 35℃, with the most active yeast at 35℃. So by controlling the temperature of the dough to create the most comfortable environment for the yeast to ferment, we can get them to multiply and ferment faster. Yeast ceases to be active and goes dormant at temperatures below 4℃, while above 40℃ it becomes less active and dies when temperatures reach 60℃ or more.
- Concentrated sugar content
We all know that adding sucrose to the dough provides nutrients to the yeast, which is why a nutritious bread with added sugar takes less time to ferment than a simple bread without sugar. Sucrose is broken down into glucose by converting enzymes and can then be used directly by the yeast. However, it is not true that the more sugar there is the faster the fermentation, as high levels of sugar can cause the osmotic pressure of the dough to rise and inhibit the growth and development of the yeast.
- Salt content
Salt has the effect of inhibiting the growth of microorganisms, and yeast is no exception. Adding the right amount of salt to the dough slows down the fermentation of the yeast, lengthens the fermentation time and allows the dough to release the flavour of the grains more fully. Also do not stack salt directly on top of the yeast, as this can easily lead to its death.
The above points are the main factors affecting yeast fermentation, but of course there are other added substances that can also have an effect on yeast fermentation, such as milk powder, oils and fats, etc., but these have a relatively small effect, so they are not discussed here.
The Role of the Different Fermentation Stages of Bread
The primary fermentation, also known as the main fermentation, is the main part that allows the hydrolysis of the starch and the production of fermentation products by the yeast.
By carrying out a primary fermentation, the dough is filled with alcohol and carbon dioxide gas produced by the yeast and the dough becomes sponge-like in structure, which is responsible for the fine structure of the baked bread. The temperature and speed of the primary fermentation should not be too high or too fast, otherwise the yeast will not be able to break down the sugars sufficiently to produce flavour substances, which will affect the taste of the bread.
The second fermentation, also known as the final fermentation, is the main part of the process that makes the bread expand in volume.
After the first fermentation and the venting of the dough, the large air bubbles inside the dough are eliminated, but numerous small bubbles remain. The second fermentation allows the dough to produce more of these bubbles, resulting in a significantly larger, fluffier and softer loaf. As the primary fermentation has already produced enough fermentation products, this stage can be set at a higher temperature than the primary fermentation to speed up the fermentation.
The most common method of primary fermentation is to cover with cling film at room temperature.
We can use this method when the ambient temperature is above 25℃. Knead the dough, place it in a greased or floured bowl and cover it with cling film and leave it at room temperature.
The purpose of covering with plastic wrap is twofold: to prevent the dough from drying out and to maintain the humidity in the bowl.
If the ambient temperature is low or if secondary fermentation requires a faster fermentation rate, we can use a fermenter for fermentation.
The advantages of a fermenter are obvious, as the temperature and humidity are accurately controlled and do not vary according to the external environment, making the fermentation environment very stable and the fermentation more efficient.
Well, If you don’t have a fermenting oven, you can use the fermentation function of your oven.
Every oven has a temperature difference and when we use the oven fermentation function, we must first test the actual temperature of the oven. The default oven fermentation temperature is 38℃, so if the oven is actually high, it can seriously affect the yeast fermentation and even cause it to die.
The solution to a high oven fermentation temperature is simple: place a thermometer in the oven, turn the oven on and off to the correct temperature, then put in hot water. Keep an eye on the internal temperature of the oven and if it is high, open the oven door to lower the temperature, if it is low, turn the oven on again for a short while.
If you don’t have access to an oven, you can also find a sealed box such as a storage box and put the dough into it with hot water, it will ferment just as well, but it may take a little longer and you will need to change the hot water regularly.
How Can I Tell the State of Fermentation?
The methods used to ferment dough were described earlier, now let’s look at how to judge the degree of dough fermentation in practice.
We can feel the state of fermentation of the dough through the five senses, using seeing, smelling and touching.
Look – observe the volume expansion of the dough.
Generally speaking, we need to increase the volume of the dough to 2 and 2.5 times its size in one fermentation. However, it is actually not very easy to see how many times it has grown through visual observation. We can cut off a small portion of the main dough into a small measuring cup and measure the volume of the dough, then place it in the same environment with the main dough to ferment, and after a period of time observe the volume of the dough in the measuring cup to get an idea of the degree of fermentation.
Once you have experience, you can basically judge the state of fermentation of the dough within the set time.
Volume after 10 minutes of kneading
Volume after 60 minutes of kneading
Smell – The smell of the dough is perceived through the nose.
When the dough is not fully fermented it has a yeasty smell and when it is over-fermented it has a stronger alcoholic smell, there is a clear difference between the two smells.
Touch – See how the dough feeds back by pressing it with your fingers.
This method is also known as finger pressure and is the most common method we use for primary fermentation. Dip your finger in dry flour and insert it in the middle of the dough to a depth of one-third, then lift your finger and the dough does not spring back or collapse, indicating that the fermentation is just right. The principle behind this is that when the dough is in place, the amount of gas in the dough is close to the limit of what the gluten can wrap around it, and the gluten is no longer very elastic, so it will not spring back when pressed. The gluten is still a little stretchy, so it won’t collapse immediately.
You can also use finger pressure during the second fermentation, but not by inserting your fingers directly, which would damage the already shaped dough.
We can use gentle pressure on the surface of the dough and if the dough springs back slowly or does not spring back, again the fermentation is at the right level. If the dough collapses when pressed, it has over-fermented. If the dough springs back immediately, it has not fermented properly.
The above three methods will be used together in practice
We’re not as accurate as the sensors, so we can only judge more accurately by feeling through more than one sense.
Q & A in Bread Fermentation
Coarse tissue in the finished bread?
R. Inadequate primary fermentation
A. Ferment fully until the dough is more than 2 times its size
More air bubbles on the surface of the bread?
R. Dough not deflated properly
A. After the primary fermentation, the dough should be fully exhausted and the large air bubbles should be pressed out
The dough does not expand in the second fermentation?
R. Excessive primary fermentation will cause the dough to consume too much nutrients, resulting in a lack of food for the yeast in the secondary fermentation
R. The dough does not have enough gluten and is not kneaded enough
A. Take care to control the duration of the primary fermentation.
A. Knead the dough in place according to the type of bread to be made, toast should be kneaded to 100% gluten and ordinary sweet bread to 90%.
Fourth, the sour taste of bread is very heavy?
R. Over-fermentation of dough
A. Pay attention to control the degree of primary and secondary fermentation
The whole fermentation process is very slow?
R. Yeast loses its activity
R. Ambient temperature is too low
A. Test the activity of the yeast before use by melting it in warm water at about 40°C and adding the right amount of sugar and stirring it well, then after 10 minutes observe if the yeast produces gas.
A. Use an oven or fermenter when the ambient temperature is very low for primary fermentation.
If baking used to be a matter of experience and skill, nowadays it is more a matter of science.
Bread making is a science in itself, and it is not enough to rely on mere words of experience. If you want to master the art of bread making quickly, you should first build up a good theoretical foundation.
For beginners, most problems with fermenting bread are due to a lack of kneading, and a lack of gluten means that the dough does not retain the gas produced by the fermentation, which naturally makes it prone to failure.
Therefore kneading and fermentation go hand in hand and it is important to get these two foundations right in order to produce a more successful loaf.
Timexing hopes this post will help you
Share More people Timexing needs your upvotes!