Opening——Whether you are a baker or a baking enthusiast, in order to bake well, in addition to making things according to the recipe, we must also learn more about the ingredients in our hands. Only by knowing them better can you Control the overall situation and make soulful dishes.
What is yeast?
There are countless yeasts floating in the air we breathe. Yeasts also exist on the surface of fruit peels, soil and plants. There are more than 500 known types of yeasts.
Yeast is the first fungus discovered and used by humans. As early as thousands of years ago, humans learned to use yeast to make wine and make bread.
Yeast generally refers to a variety of single-cell fungi that can ferment sugars. It can survive in aerobic and anaerobic environments, and it likes acidic, humid and sugary environments. Most of the yeast we use daily is Saccharomyces cerevisiae (bread yeast/brewer’s yeast)
Type of yeast
Fresh yeast is pale yellow lumpy yeast. The yeast contains about 70% water. It is easy to dissolve in water and not easy to agglomerate when used. It needs to be refrigerated or frozen for storage. The dosage is about 3 times that of ordinary dry yeast. Fresh yeast, also known as squeezed yeast, is dehydrated by squeezing Saccharomyces cerevisiae. It is not used in large quantities because it needs to be refrigerated and has a validity period of only 2-3 months.
Dry yeast is dehydrated fresh yeast, with a water content of about 8%, and it is in the form of fine particles. It needs to be dissolved in water before use. When I was a child in the north, my mother used this yeast to make steamed buns. Every time I use it Melt the yeast in a bowl of warm water first, then add the water to the flour. Compared with fresh yeast, it has a longer shelf life and is more durable for storage and transportation.
High active dry yeast
Highly active yeast is based on dry yeast, using genetic engineering technology to cultivate a strain of Saccharomyces cerevisiae with high resistance to drying. It is made through a special nutritional ratio. It has lower water content and smaller particles than dry yeast, and it is not easy to use when used It needs to be dissolved in water first, and can be added directly to the dough.
Note: Salt has a bactericidal function and can inhibit the growth of yeast. When making bread, bakers will deliberately separate the salt and yeast. This is to prevent the salt and yeast from mixing together after adding water, reducing the activity of yeast. The higher the salt content in the flour, the more affected the proofing will be.
In addition, yeast is difficult to dissolve in fat. Brioche of French bread is a bread without water. It uses pure eggs and butter to make dough, so when making this bread, a small part of milk is usually used to dissolve the yeast. Melt into a puree and add to the dough and stir together.
Tea yeast is a popular topic in recent years, because it is used in the field of weight loss.
Tea yeast contains tea polyphenols, which have super antioxidant capacity, 10 times more than vitamin E, and can effectively reduce blood lipids and make people look radiant. Tea yeast was first discovered during the low-temperature fermentation of oolong tea. The yeast precipitated at the bottom. At this time, the yeast absorbed the essence of the tea, and the precipitated yeast was collected, cleaned, disinfected, and dried. This became tea yeast.
Living conditions of yeast
Bakers have an inseparable relationship with yeast. From the earliest discovery of yeast to the present, there has been a long history of more than 4,000 years. For thousands of years, bakers and yeast have been in a partnership relationship. Before the industrialization of yeast, bakers needed to feed their yeast liquid with new nutrients every day to keep it active. Yeast through a steady stream of nutrients , to produce carbon dioxide to help the dough expand and proof.
Yeast is a heterotrophic organism that can survive both aerobic and anaerobic. Like other living organisms, it needs nutrients to survive. It decomposes substances from polysaccharides into absorbable monosaccharides through its own intracellular and extracellular enzymes .
As mentioned earlier, yeast likes an acidic, humid and sugary environment, so it can survive under specific conditions, that is, a suitable temperature, suitable humidity, suitable acidity, and a sugary environment.
- It can survive in an acidic environment with a pH value of 3.0-7.5
- It must have water to survive, which is why yeast powder contains water. Due to the development of science and technology, the production of highly active yeast is due to the cultivation of yeast that is more resistant to drying, so that the yeast can be more dry. Capable of storage under extreme conditions.
- Yeast will stop growing below 0°C or above 47°C, and the most suitable growth temperature is 20-30°C.
The Lubang species (natural yeast species) of traditional European-style bread uses this method to cultivate and produce yeast. Using the reproductive characteristics of yeast, it creates an environment suitable for growth and reproduction, and reproduces a large number of new yeast. Yeast Bacteria use sugar in flour as nourishment (that is, decompose amylase in flour), continuously metabolize sugar in flour and gradually absorb it, and then keep Lubang species active by adding new nutrients (flour) for continuous cultivation. We call this The method of continuous cultivation is called continuous planting. Such continuous planting training method can not only ensure that there is a steady stream of Lupine species that can be used, but also dilute the harmful substances produced by metabolism.
Uses of yeast:
Aerobic fermentation: As mentioned above, yeast can survive under aerobic and anaerobic conditions. Our bread proofing belongs to aerobic fermentation using yeast. The steps of aerobic fermentation are as follows:
Yeast converts sugars
(glucose, fructose, sucrose)
Decompose water + carbon dioxide + energy (yeast is the most active and can reproduce rapidly)
When the bread is baking/cooking, if the temperature rises above 47°C, the yeast will gradually die, the carbon dioxide in the dough will expand, the alcohol will volatilize, and the dough will become very soft. Due to a series of chemical reactions of the yeast in the dough, the bread has a unique flavor. The combination of the aroma of wheat, the aroma of dairy products contained in the dough and the aroma of fermentation is very charming.
Anaerobic fermentation: In the absence of oxygen, yeast break down sugars in starches to produce alcohol, a process known as winemaking. Different wine crafts are also different.
Yeast converts sugars (glucose, fructose, sucrose)
Break down alcohols (ethanol/alcohol)
carbon dioxide + energy
Most of the famous wines in China are sorghum wine, which is a kind of distilled wine. The principle of making wine is similar to that of making bread, but the purpose is different. The practice of baijiu is to make distiller’s koji first, and then make distiller’s koji through the yeast that spreads in the air, then cook the grain and mix it into the distiller’s koji, and seal and ferment at the suitable growth temperature of the yeast. At this time, under the action of the yeast and the starch in the grain, Alcohol is produced. Grains contain protein, which is hydrolyzed into amino acids during the fermentation process. Amino acids are transformed into higher alcohols through the action of yeast. Higher alcohols are the source of aroma of grain wines. Key reason for no.
There are still many foods in our life that are fermented by yeast, such as cheese, yogurt, soybean paste, stinky tofu, soybean juice, etc. Fermentation has produced subtle chemical changes in these foods, and this evolutionary upgrade has also made foods Rich and varied.