It is suggested that when making yogurt, try to choose fresh milk, buy a bucket of yogurt with your favorite taste as a strain, and the amount of sugar you like is good.
Yogurt is a kind of dairy product which takes milk as raw material, adds beneficial bacteria (starter) to pasteurized milk, ferments, and then cools and fills. At present, most yogurt products on the market are solidified, stirred and fruity with various juices and jams. Yogurt not only retains all the advantages of milk, but also exerts its advantages and avoids its weaknesses in some aspects, making it a more suitable nutritional health care product for human beings.
The production process of yogurt can be summarized as batching, preheating, homogenization, sterilization, cooling, inoculation, (filling: for solidified yogurt), fermentation, cooling, (stirring: for stirred yogurt), packaging and post-ripening. Modified starch is added in the batching stage, and its application effect is closely related to process control:
Ingredients: select the required raw materials according to the material balance table, such as fresh milk, sugar, stabilizer, etc. The modified starch can be added alone or after dry mixing with other edible gums. Considering that starch and edible gum are mostly highly hydrophilic polymers, it is best to mix them with proper amount of sugar and dissolve them in hot milk (55℃ ~ 65℃, the specific temperature depends on the description of modified starch) under high-speed stirring to improve their dispersibility.
Preheating: The purpose of preheating is to improve the efficiency of the next process-homogenization, and the preheating temperature should not be higher than the gelatinization temperature of starch (to avoid the particle structure being destroyed in the homogenization process after starch gelatinization).
Homogenization: Homogenization refers to the mechanical treatment of milk fat globules so that they are evenly dispersed in milk in the form of smaller fat globules. In the homogenization stage, materials are subjected to three forces: shear, collision and cavitation. Modified starch starch has strong mechanical shear resistance after cross-linking, which can maintain the complete particle structure and is beneficial to maintain the viscosity and posture of yogurt.
Sterilization: pasteurization is generally adopted, and the sterilization process at 95℃ and 300S is generally adopted in dairy plants. At this stage, the modified starch is fully expanded and gelatinized, forming viscosity.
Cooling, inoculation and fermentation: Modified starch is a high molecular substance, and compared with the original starch, it still retains some properties of the original starch, that is, the properties of polysaccharide. In the pH environment of yogurt, starch will not be degraded by bacteria, so the stability of the system can be maintained. When the pH value of the fermentation system drops to the isoelectric point of casein, casein denatures and solidifies, and the skeleton of the three-dimensional network system of casein micelle connected with water becomes curd-like. At this time, gelatinized starch can fill the skeleton, bind free water and maintain the stability of the system.
Cooling, stirring and post-ripening: The purpose of cooling stirred yogurt is to quickly inhibit the growth of microorganisms and the activity of enzymes, mainly to prevent excessive acid production during fermentation and dehydration during stirring. There are many sources of modified starch raw materials, and the degree of denaturation is different. Different modified starches have different functions in yogurt production. Therefore, according to the different requirements of yogurt quality, corresponding modified starch can be provided.
The specific manufacturing method is as follows:
The instruments and materials for making yogurt include sterilization equipment, fermentor or fermentation chamber, heating tank, ultraviolet lamp, glass bottle or porcelain bottle or special paper basin, fresh milk, sugar, lactic acid bacteria (Bulgaria bacillus and Streptococcus thermophilus) and so on.
Production steps:
Sterilization of glass bottles, etc. The glass bottles are sterilized in the sterilizer for half an hour, the steamer takes 45 minutes, the inoculation room needs ultraviolet sterilization for 50 minutes, and the inoculation tools need to be sterilized in the autoclave for 30 minutes.
Milk sterilization. Put fresh milk in a heating tank, add 10 ~ 12% sugar, and sterilize at 85 ~ 90℃ for 30 minutes or by other methods. No matter which method is adopted, it is best not to destroy the original nutrients of milk, and then cool it after sterilization. Before or during sterilization, it is best to remove the upper grease to defat the milk.
Vaccinate. Sub-package the sterilized milk with the temperature below 43℃ into sterilized glass bottles, inoculate it into the inoculation room according to the inoculation amount of 2% ~ 4% of the milk, and stir evenly. Pay attention to canning without gaps, and seal it immediately after connection to ensure lactic acid.
Anaerobic fermentation conditions. Then it is sent to the cold storage at 0 ~ 5℃ for refrigeration and ripening for 8 ~ 10 hour, and then it can be put on the market for sale. After-cooked yogurt has a special aromatic smell because it contains esters. On the one hand, the function of refrigeration can prevent the increase of acidity and the pollution of miscellaneous bacteria, on the other hand, it can make the texture compact and recover whey, thus greatly improving the stability of yogurt quality. In the whole process, attention should be paid to aseptic operation. Workers should wear sterile overalls, sterile gloves and masks, and clean their hands. They must be vaccinated without masks to prevent all kinds of bacterial pollution.
Quality standards. The appearance of high-quality yogurt is milky white or yellowish, the surface is smooth, the curd is firm, the tissue is delicate, the texture is uniform, a small amount of whey is allowed to precipitate, there is no bubble, the sour and sweet taste is moderate, and there is no pungent smell or other peculiar smell. If there are bubbles in yogurt, the bottle cap bulges or has pungent odor, it means that fresh milk is polluted by miscellaneous bacteria during fermentation.
Edible. If the seed (koji) produced has the above situation, it must not be used for production to prevent unnecessary losses. If it is overtime at an appropriate temperature, there is little milk coagulation, whey precipitation, or even no milk coagulation, and a large number of suspended substances appear, which indicates that the strain has been seriously degraded or contaminated by miscellaneous bacteria and should be stopped. If the strain declines, the declining strain can be cultured on inclined culture medium, purified and rejuvenated, and then propagated to obtain excellent production strain.
Self-made method
Room temperature above 30℃ is enough in summer. Only the coagulation time is longer, and the higher the room temperature, the shorter the coagulation time. The method is to clean coarse glass bottles or porcelain bottles (cans can't be used because the bottle mouth is too big and easy to be polluted by miscellaneous bacteria), put milk on it, cover the bottle mouth with clean double-layer plastic film and tie it tightly with string. The rope should be loosened, because a lot of steam will be generated in the bottle during heating. If it is tied too tightly, the membrane will rupture and pollution will easily occur. Boil the glass bottle and milk in the pot for 30 minutes. Soak until there is no milk surface. Don't cover the pot. Then take out 2% ~ 4% fresh pure yogurt sold in the market and cool it until the back of your hand is not hot. After adding the bought yogurt, immediately tie the plastic film tightly to ensure the oxygen-free environment in the bottle. At room temperature 10 hour later, fresh milk solidifies like tofu brain and yogurt is served. Put the yogurt bottle in the refrigerator at 0 ~ 5℃ for 2 ~ 4 hours, and you can eat it. White sugar can be added during sterilization or when eating, depending on personal taste. You can make a small bottle alone when cooking. If the curd is good, you can keep it as a strain, but you can't use it many times. Because aseptic operation can't be guaranteed at home, you can put the strains in the refrigerator. If the film on the bottle mouth bulges and gas is generated inside, it means that it has entered the gas-producing bacteria, which can only be eaten and cannot be preserved as a strain.