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Analysis of Factors Affecting Yeast Fermentation and Evaluation of Yeast Quality

yeast fermentation

Analysis of factors affecting yeast fermentation:

1. The influence of temperature. The optimum temperature for yeast growth is between 26-28°C, and the optimum temperature is 28°C. Therefore, when the dough is proofed, the temperature of the fermentation room should be controlled below 30℃–32℃, so that the yeast can multiply in large quantities and accumulate stamina for the proofing of the dough. The activity of yeast increases with the increase of temperature, and the gas production also increases greatly. When the dough temperature reaches 38 °C, the gas production reaches a large amount, and the high temperature of the dough should not exceed 40 °C. The lethal temperature of yeast is 60°C

2. The effect of pH. Yeast is suitable for growth in an acidic environment, and its activity is greatly reduced under alkaline conditions. When the yeast is fermented, the proper pH value of the dough should be controlled between 5-6.

3. The influence of osmotic pressure. If the dough contains more sugar, salt and oil and other ingredients, it will produce osmotic pressure. As mentioned above, high-fat and high-sugar dough must use high-sugar-tolerant yeast.

4. The influence of water quality. A softer dough with more water will ferment faster and vice versa. Hard water should increase the amount of yeast, soft water should reduce the amount of yeast.

Yeast quality evaluation key indicators:

– Fermentation power. The national standard stipulates that the fermentation power measurement is to make dough with certain flour and yeast, and use the drainage method or SJA vitality tester to measure the gas production in one hour. However, due to the different strain characteristics or production processes of various yeast companies, the actual use of yeast is different. In addition, special attention should be paid to the difference between high and low sugar yeasts. If low sugar (sugar free) yeast is used in dough with more than 7% sugar added to flour, the yeast fermentation power is very poor; on the contrary, if high sugar tolerance yeast Yeast leavening power is also poor when used in doughs with less than 5% sugar added to the flour. High-sugar-tolerant yeast with high osmotic pressure must be used for heavy oil bread.

– Stamina or expansion into the furnace. The fermentation time of making bread is relatively long, and the process of making steamed buns is relatively slow. These two products need to use products with sufficient fermenting stamina. Especially for bread, PK is the height of the finished bread after baking, not the height of the yeast dough before it is put into the oven. Some yeast doughs are taller before entering the oven, but they fail after being baked in the oven, which is the reason for the poor expansion in the oven. The pros and cons of yeast for baking and pastry are mainly reflected in this indicator. Of course, adding some bread improvers will help improve the expansion in the oven.

– Control of miscellaneous bacteria. The better the control of yeast and miscellaneous bacteria, the better the fermentation flavor of bread and steamed buns, and the longer the product shelf life, especially for long-term fermentation dough. Yeast production is all produced in sanitary pipelines and equipment, and the control requirements for miscellaneous bacteria are relatively high. You usually buy yeast at various price points, and it seems that there is little difference, but this is not the case. High-quality yeast requires high fermentation power, sufficient stamina and good expansion into the furnace, as well as high requirements for the control of miscellaneous bacteria. It needs to be controlled from the raw materials, and then the hygiene management of the workshop personnel, and the number of cleaning and sterilization of equipment needs to be increased. As a result, the cost is increased, and the price is much higher.

– Sensory Index. Color, Odor, Granularity and Solubility. The color should be light yellow, and the smell should be the special aroma of yeast, no corruption, no peculiar odor. If the yeast has a peculiar smell or a savory smell, it means that the yeast has deteriorated and must not be used. In this case, the yeast fermented dough No problem, but will give your bread pastry an unpleasant taste. Yeast particles should not be too large, too large particles will affect solubility and dispersibility, which in turn will make your product uneven.


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