Analysis of factors affecting the quality of ice cream 2005-6-291:18: 41Internal data research and development Ice cream is a frozen dairy product, and its physical structure is a complex physical and chemical system, with bubbles dispersed in a continuous liquid with ice crystals, which contains fat particles, milk proteins, insoluble salts, lactose crystals and colloids. Please refer to the national industry standard SB/T 100 13-99 for the quality standard of ice cream. In order to make ice cream meet the specified quality standards and physical structure, the composition of ice cream mixture (formula and quality of raw and auxiliary materials), production process conditions and production equipment should be analyzed and studied. 1, the influence of ingredients of ice cream mixture The main raw materials for making ice cream are fat, non-fat solids, sweeteners, emulsifiers, stabilizers, spices and pigments. 1. 1 The fat commonly used in fat ice cream is cream, which can give ice cream a unique aromatic flavor, tissue lubrication, good texture and shape retention, so generally speaking, the more cream, the better the quality. The sources of milk fat are pure cream, cream, fresh milk, condensed milk, milk powder and so on. And be sure to choose fresh, clean and good quality. However, cream is the most expensive ingredient in ice cream raw materials, and its usage is limited. In China and many countries in the world, a considerable amount of vegetable fat is used to replace milk fat, mainly margarine, hydrogenated oil, palm oil, coconut oil and so on. Its melting point should be similar to that of milk fat, at 28-32℃. 1.2 Non-fat milk solids Non-fat milk solids are the general name of protein, lactose and minerals left after fat removal from total milk solids, in which protein is hydrated. In the process of homogenization, a stable film is formed on the surface of the generated fat pellets together with the emulsifier, which ensures the emulsification stability of oil in water and promotes the full mixing of air during freezing. It can also prevent the expansion of ice crystals in the product, so that the smooth texture of the product, the soft sweetness of lactose and the light salty taste of minerals give the product remarkable flavor characteristics. However, if there are too many non-fat solids, the unique creamy smell of fat will be eliminated, resulting in the smell of condensed milk or skim milk powder, which limits the use of non-fat milk solids. The biggest reason is to prevent the sand-like precipitation from the gradual crystallization of lactose. It is generally recommended that the maximum consumption of lactose should not exceed 65,400% of the water in ice cream. 1.3 The most commonly used sweetener is sucrose, and the general dosage is 15%~ 16%. Sucrose not only makes the product sweet, but also makes the product delicate, so it is a high-quality and low-cost sweetener. The amount of sucrose can reduce the freezing point of ice cream mixture. In view of the anti-crystallization effect and soft sweetness of starch syrup, starch syrup is often used to partially replace sucrose abroad, and it is also widely used by domestic ice cream manufacturers at present. Because the freezing point of starch syrup is lower than sucrose, it should not be used too much. Generally, it is better to use 1/4 sucrose instead. At this time, 1.5kg starch syrup can replace about 65438 sucrose. When sucrose and starch syrup are used together, the texture of ice cream will be better, and it has the advantage of preventing the quality from declining during storage and transportation. Most sorbet, sherbet or fruit ice cream containing fruit juice need to be sweetened because of its sour taste. For products with strong bitterness such as cocoa or sweet juice, sucrose should be increased by 2%-3% compared with ordinary ice cream. In order to improve flavor, increase varieties or reduce costs, many sweeteners, such as honey, saccharin, sodium cyclamate, aspartame, stevioside, etc., are used together. 1.4 stabilizer is hydrophilic, that is, it can combine with water, so it can improve the viscosity and expansion rate of ice cream, prevent the generation of ice crystals, reduce the roughness and make the product smooth. And its water absorption is strong, so it has strong resistance to product melting, which makes ice cream not easy to melt and can play a role in improving the organizational state in ice cream production. There are many kinds of stabilizers, such as gelatin, CMC, guar gum, xanthan gum, carrageenan, seaweed gum, konjac gum, modified starch and so on. Starch is generally used for low-grade ice cream. The addition amount of stabilizer varies with the ingredients of ice cream, especially according to the total solid content, which is generally about 0. 1%~0.5%. No matter which stabilizer has its advantages and disadvantages, it is best to mix two or more stabilizers separately. The following points should be considered when selecting stabilizers: ① Soluble in water or mixture. ② endow the mixture with good viscosity and foamability. ③ It can give ice cream a good texture and texture. ④ It can improve the shape retention of ice cream. ⑤ It can prevent crystallization from expanding. ⑥ Cheap emulsifier 1.5 emulsifier is a substance with hydrophilic groups and lipophilic groups in its molecule, which can be between oil and water, so that one side can be well dispersed in the other side to form a stable emulsion. The composition of ice cream is complex, and adding emulsifier to its mixture has other functions, which can be summarized as follows: ① Make fat balls in a delicate and turbid state and make them stable. ② Disperse and stabilize particles other than fat globules. ③ Increase the heat resistance of ice cream at room temperature. ④ Reduce the change of products during storage. ⑤ Prevent or control the formation of coarse ice crystals, and make the ice cream delicate. Emulsifiers commonly used in ice cream include glyceride (monoglyceride), sucrose fatty acid ester (sucrose fatty acid ester), polytrimethylene ester (Tween), sorbitan fatty acid ester (Span), propylene glycol fatty acid ester (PG ester), lecithin and soybean lecithin. Recently, Taiyuan Daily Chemical Institute developed monoglyceride stearate, which is a new type of food emulsifier, and its emulsifying effect is equivalent to that of molecular distillation monoglyceride. Generally, it increases with the increase of fat content, and its range is between 0. 1%-0.5%. Similarly, the performance of composite emulsifier is better than that of single emulsifier. 1.6 total solids total solids are the sum of the above raw materials, which is the main factor affecting the quality and expansion rate of ice cream. Generally, those with high solid content can improve the expansion rate and output, the structure will become lubricated and the quality will be improved, which has the advantage of reducing the heat required for freeze hardening. But if the solid content is too high, the viscosity of the mixture will increase, which will make the texture worse and increase the cost. Generally, the solid content is 25%-40%. 1.7 Spices and essences can make products with mellow fragrance and natural flavor of this variety. Its quality directly affects the quality of ice cream, so when choosing to use it, besides considering the price factor, the first thing to pay attention to is the quality. 2, the influence of ice cream production process conditions, the production process of ice cream must be completed according to certain technical conditions, otherwise it is impossible to produce good quality products. 2. 1 Inspection of raw materials The quality of raw materials directly affects the quality of ice cream. Therefore, all kinds of raw and auxiliary materials must be inspected in strict accordance with quality standards, and unqualified materials are not allowed to be used. Sensory examination is usually carried out first. At the same time, the specific gravity, viscosity, solid content, fat content and sugar content were determined. The raw materials are tested to see whether they meet the specifications, whether their bacterial count, arsenic content, lead content and other heavy metals are lower than the legal standards, and whether the food additives used meet the requirements. 5.2.2 ingredients mixing 5.2.2. 1 calculation of raw materials The most basic thing to make ice cream is ingredients, that is, formula calculation. The formula composition of ice cream is determined by consumer's preference, raw material price and supply, product sales and other factors. Firstly, the quality standard is determined, and then the demand of various raw materials is calculated by mathematical method according to the standard requirements to ensure the product quality meets the technical standards. Before calculation, you must first know the ingredients of various raw materials and ice cream as the basis for formula calculation. The material balance method is used for formula calculation. For the general rules of formula calculation and the amount of raw materials, see the production process (III). 2.2.2 Preparation of Mixture The preparation of mixture should first weigh all kinds of raw materials according to the formula proportion, and then prepare them in the batching tank. The mixing sequence of raw materials should start from low-concentration liquid raw materials such as water and milk, then liquid raw materials such as condensed milk and thin cream, and then solid raw materials such as sugar, milk powder, emulsifier and stabilizer. Finally, adjust the capacity with water, milk, etc. The temperature of mixing and dissolution is usually 40-50℃. Milk powder should be dissolved in water before preparation, homogenized once, and then mixed with other raw materials. Sugar should be added with appropriate amount of water, heated, dissolved and filtered. The compound emulsion stabilizer for ice cream can be mixed with sugar for more than 5 times, and then added into the mixing tank under the condition of continuous stirring to fully dissolve and disperse it. 2.3 The acidity of the sterilization mixture and the sterilization method adopted have a direct impact on the flavor of the product. The acidity of the mixture should be 0. 18%~0.20% lactic acid. When the acidity is high, it should be neutralized with calcium hydroxide or baking soda before sterilization. Otherwise, sterilization will not only cause protein solidification, but also affect the flavor of the product. However, attention should be paid to prevent astringency caused by excessive neutralization. When the ice cream mixture is heated to 78℃ by jacketed steam in a sterilization tank, the temperature is kept for 30 minutes for sterilization. If continuous pasteurizer is used for high-temperature instantaneous sterilization (HTST), 83~85℃ and 15s are the most widely used. Otherwise, long-term sterilization at high temperature will easily lead to cooking and burning taste of products. 2.4 Homogenization of homogeneous mixture has an important influence on the shape and structure of ice cream. Homogenization is generally carried out by two-stage high-pressure homogenizer, which can reduce the diameter of fat globules, generally reaching 1~2μm, and increase the viscosity of the mixture to prevent fat from being stirred into cream particles during freezing, thus ensuring the delicate texture of ice cream products. The optimum homogenization temperature is 65~70℃, and the first stage homogenization pressure is 15-20MP. 2.5 cooling, aging aging is to refrigerate the mixture at a low temperature of 2~4℃ for a certain period of time, which is called "aging" or "ripening". Its essence lies in the hydration of fat, protein and stabilizer. The stabilizer fully absorbs water to increase the viscosity of feed liquid, which is beneficial to the increase of expansion rate during freezing and stirring. The aging time is related to the temperature of feed liquid, the composition of raw materials and the type of stabilizer, and it is generally aged at 2~4℃ for 4 ~ 24 hours. When aging, attention should be paid to avoid contamination by miscellaneous bacteria, and the aging cylinder must be strictly disinfected in advance to ensure the hygienic quality of the products. 2.6 Freezing and freezing process is the process of freezing the mixture under forced stirring, so that air is evenly distributed in all the mixture in the state of tiny bubbles, and a part of water becomes tiny ice crystals. Its function is as follows: (1) The temperature of the ice cream mixture decreases, the viscosity increases, and it gradually thickens into a semi-solid state, that is, a frozen state. (2) Due to the agitation of the agitator, the scraper continuously scrapes off the materials on the cylinder wall to prevent the mixed raw materials from forming large ice cubes on the cylinder wall. (3) Due to the continuous stirring and cooling of the agitator, the air is gradually mixed during the freezing process, which makes the volume of ice cream expand and the ice cream reaches a beautiful structure and a perfect shape. The freezing temperature is -2~-4℃, the freezing time of intermittent freezer is 15~20 minutes, the discharging temperature of ice cream is generally -3~ -5℃, the discharging temperature of continuous freezer is continuous, and the discharging temperature of ice cream is about -5~ -6℃. Continuous freezing needs to check the expansion rate frequently to control the appropriate inlet, outlet and mixed air. 2.7 The ice cream after molding, filling and freezing must be molded and hardened immediately to meet the needs of storage and sales. Ice cream molding has various molding and filling machines, such as ice anvil, paper cup, egg cone, mold molding, chocolate coated ice cream, special-shaped ice cream cutting line and so on. Their weights are 320g,160g, 80g, 50g, etc. , and household 1kg. 2.8 Frozen, hardened and stored ice cream is soft ice cream without hardening. If you pour it into a container and then harden it, it becomes hard ice cream. The former is mostly sold in shops, while the latter has a large output. The purpose of quick freezing and hardening is to quickly freeze the ice cream (-3~-5℃) coming out of the freezer at low temperature (