Scientifically understand yeast, Yeast is food and can be used with confidence. The national standard GB2760 has clear regulations. The traditional Chinese method of making old noodles also uses the principle of yeast fermentation
1. Scientific understanding of yeast:
Yeast is food and can be used with confidence. The national standard GB2760 has clear regulations.
The traditional Chinese method of making old noodles also uses the principle of yeast fermentation. The old noodles gather various bacteria in the air, including lactic acid bacteria and a large number of yeasts, and add them to the flour. The yeast is mainly fermented to produce carbon dioxide to make the dough become It is fluffy, but due to the existence of miscellaneous bacteria, the dough produces acid, and it has to be neutralized with alkali, otherwise, yellow steamed bread and dead steamed bread will appear. With the development of modern biotechnology, people have been able to produce high-content pure yeast through large-scale fermentation, which can be widely used in baking, pastry, condiments, biological fermentation medium, health care products and cosmetics and other industries.
Yeast is not only rich in protein and carbohydrates, but also contains a variety of B vitamins and trace elements such as calcium, iron, zinc, and magnesium. Studies have shown that the protein contained in 1 kg of dry yeast is equivalent to the protein content of 5 kg of rice, 2 kg of soybeans or 2.5 kg of pork. In addition, the protein composition of yeast is close to that of meat, and it is a complete protein. The rich lysine and tryptophan contained in yeast can make up for the lack of lysine and tryptophan in grains and achieve a balanced nutritional effect.
Yeast cells are rich in hydrolytic enzymes, which can hydrolyze starch, cellulose, and protein into low-molecular-weight sugars and amino acids, which are easily digested and absorbed by the human body, and improve the digestion and absorption rate of flour. Phytic acid in flour can form chelates with minerals such as calcium, iron, and zinc, which inhibit the absorption of these minerals by the body. Yeast contains phytase, which can effectively hydrolyze the phytic acid in the flour during the fermentation of the dough, which helps the body to absorb zinc, iron, calcium, etc. Yeast is a commodity that has long been standardized and has strict national standards. Using it to make bread, steamed buns and steamed buns can ensure the hygiene and safety of the products; yeast can make the dough fermentation proceed stably and meet the needs of industrial production; The problem of aluminum damage that may occur when excessive addition of flour to make steamed bread; yeast steamed bread is more nutritious and tastes better, which has been accepted by more and more people.
2. Classification of food highly active yeast
(1) Active dry yeast: Active dry yeast is a dry yeast product that maintains strong fermentation ability after the cultivated yeast is pressed, dried and dehydrated. The pressed yeast is extruded into thin strips or small balls, and the circulating air with low humidity is used for continuous drying through the fluidized bed, so that the final fermentation moisture reaches about 8%, and the fermentation capacity of the yeast is maintained. Since the activity and shelf life of this yeast cannot meet the industrialization needs of bread and pastry, it is gradually rare in the market.
(2) High active dry yeast: Instant active dry yeast (IDY) is also called high active dry yeast. Compared with active dry yeast, it has a water content of 4% to 6%, small particles and fast fermentation speed. It can be used directly. Most of the current products are highly active dry yeast.
Yeasts used in the baking and pastry industries are generally classified as high-sugar-tolerant yeast or low-sugar yeast. The yeast that is suitable for maintaining the fermentation power at a sugar concentration of more than 7% (calculated as flour) is called “high-sugar yeast”, otherwise it is called “low-sugar yeast”. On the label of edible high-activity dry yeast products, high-sugar-tolerant dry yeast generally has the word “high-sugar type”, and those that are not marked are generally low-sugar type dry yeast.
Raw materials such as sugar, salt and oil in bread making will generate osmotic pressure. If the osmotic pressure is too high, the protoplasm and water in the yeast will seep out of the cell membrane, resulting in the separation of the plasmodesm of the yeast cells, so that the yeast cannot maintain normal growth until death. However, the tolerance of different yeasts to osmotic pressure is very different: low-sugar dry yeast has low sugar tolerance and is suitable for making sugar-free or low-sugar staple bread, steamed bread, buns, etc.; high-sugar-tolerant dry yeast has very high sugar tolerance High, suitable for making high-sugar buns, snacks, bread, etc. Generally, the osmotic pressure of sucrose, glucose and fructose is larger than that of maltose.
This type of yeast is generally packaged in vacuum aluminum foil, and is suitable for storage in a cool and dry place. The shelf life in vacuum state is 2 years. When the bag is not used up at one time, it can be sealed with a clip and stored in the refrigerator.
(3) Semi-dry yeast. Semi-dry yeast is a medium and low temperature drying process, so that the yeast maintains about 20% moisture and has better fluidity and dispersion. Since semi-dry yeast has not undergone high-temperature drying process, the number of viable cells is less lost; at the same time, due to the high water content, it must be stored in -18°C cold chain transportation to ensure that the yeast is in a dormant state before use. The shelf life of semi-dry yeast is 24 months. It can be said that semi-dry yeast has the three advantages of fermentation power, flavor and long shelf life of dry yeast.
(4) Fresh yeast: block yeast products with a moisture content of about 70% produced by yeast companies. It is light yellow, has a compact structure and is easy to crush, and has strong baking ability. Fresh yeast should not be refrigerated for too long. If the storage time is too long, the yeast will begin to turn brown, and if the refrigeration period is prolonged, the fermentation power of the yeast will be reduced. The characteristics of fresh yeast are that the number of living cells is not lost, the flavor is good, and the activity is high.
(5) Liquid yeast: Liquid yeast is generally used for large foods with a large amount of yeast. After the yeast company has fermented the yeast, it will be cooled by centrifugal washing, pumped into a special refrigerated clean tank truck, and transported directly to the low-temperature storage tank of 0-4 degrees in a large food company, with a shelf life of no more than 3 days. The advantages of liquid yeast are high activity and good flavor, avoiding the trouble of secondary dissolution of yeast.
(6) Other special yeasts: such as freeze-resistant yeast, preservative-resistant yeast, etc. Yeasts with these characteristics are mainly screened for suitable yeast strains through strain breeding technology, or continuously domesticated through specific processes, so that commercial yeast can satisfy these special production requirements. Due to the strict restrictions on the source of yeast strains by national regulations, at present, whether it is food yeast for baking pastry or yeast for alcohol fermentation or feed, the regulations stipulate that only natural yeast strains can be used, and the strains are strictly genetically engineered. , this regulation makes major yeast companies need to invest a lot of research work in order to continuously achieve breakthroughs.
In conclusion, yeast are beneficial microorganisms and the treasure of our dough fermentation!