Ice cream is a frozen dairy product whose physical structure is a complex physical and chemical system. Air bubbles are dispersed in a continuous liquid with ice crystals. This liquid contains fat particles, milk proteins, insoluble salts, lactose crystals, and glue. The body stabilizer and sucrose, lactose, soluble salts, such a three-phase system consisting of a gas phase, a liquid phase and a solid phase can be regarded as a partially frozen foam containing 40% to 50% by volume of air. The quality standards for ice cream can be found in the national industry standard SB/T10013-99. To achieve the specified ice cream quality standards and physical structure, it should be analyzed from the composition of ice cream mix (formulation and raw and auxiliary materials quality), production process conditions and production equipment.
1. The influence of the composition of ice cream mix
The main raw materials for making ice cream are fat, non-fat solids, sweeteners, emulsifiers, stabilizers, spices and pigments.
1.1 fat
The fat commonly used for ice cream is milk fat. The milk fat can impart the unique aroma flavor, tissue lubrication, good texture and shape retention of the ice cream. Therefore, in general, the more the milk fat, the better the quality. The sources of milk fat are pure cream, cream, fresh milk, condensed milk, milk powder, etc., and must be fresh, clean and of good quality. However, milk fat is the most expensive ingredient in ice cream raw materials. Its use 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, etc., its melting point properties should be similar to milk fat, between 28-32 °C.
1.2 non-fat milk solids
Non-fat milk solids are a general term for the protein, lactose and minerals remaining in the total solids of cow's milk to remove fat. The protein has hydration properties, and it forms with the emulsifier on the surface of the formed small fat globules during the homogenization process. Stable film ensures the emulsion stability of the oil in water, while promoting good air mixing during the freezing process. It can prevent the expansion of ice crystals in the product, so that the texture lubrication, the soft sweetness of lactose and the faint salt taste of minerals will give the product a distinctive flavor characteristic. However, if there is too much non-fat solid content, the unique creamy taste of the fat will be Elimination, but condensed milk odor or skim milk powder odor will appear, limiting the amount of non-fat milk solids used, the biggest reason is to prevent the lactose in which the lactose is supersaturated and gradually crystallize the sand-like precipitate, generally recommended that the maximum amount does not exceed the ice cream 17% of the water content, non-fat milk solids can be provided by liquid milk, condensed milk, milk powder, whey powder.
1.3 sweeteners
Nowadays, the most commonly used is sucrose, which is generally used in an amount of 15% to 16%. Sucrose not only gives the product a sweet taste, but also makes the product fine and delicate, and is a high-quality and inexpensive sweetener. The amount of sucrose can reduce the freezing point of the ice cream mixture. In view of the anti-crystallization effect of starch syrup and the softness of sweetness, foreign countries often replace sucrose with starch syrup. At present, domestic ice cream manufacturers are also widely used, due to the use of starch syrup. The freezing point will be lower than that of sucrose, so it is not suitable to use too much. Generally, it is better to replace 1/4 of sucrose. At this time, 1.5kg of starch syrup can replace 1kg of sucrose. When both sucrose and starch syrup are used together, the structure of the ice cream will be better, and there is an advantage of preventing the quality from being lowered during storage and transportation.
Most juice-containing Sorbet, Sherbet or fruit ice creams have a sweet taste and weaken the sweetness. Therefore, it is necessary to add a sweetener. For products with a bitter taste such as cocoa or sweet juice, it is better to increase the ice cream by 2%. - 3% sucrose.
In order to improve the flavor, increase the variety or reduce the cost, many sweeteners such as honey, saccharin, sweetener, ghre, stevia, acetoin and the like are used together.
1.4 stabilizer
The stabilizer has hydrophilicity, that is, it can be combined with water, thereby improving the viscosity and expansion ratio of the ice cream, preventing the generation of ice crystals, reducing the rough feeling, and making the product tissue light and slippery. Moreover, its water absorption is strong, so it is also resistant to product melting, making ice cream difficult to melt, and can play a role in improving tissue state in ice cream production. There are many types of stabilizers, such as gelatin, CMC, guar gum, xanthan gum, carrageenan, seaweed gum, konjac gum, modified starch, etc., and starch is generally used in lower grade ice cream. The amount of stabilizer added varies depending on the composition of the ice cream, especially depending on the total solid content, and is generally about 0.1% to 0.5%. No matter which kind of stabilizer has strengths and weaknesses, it is better to use two or more kinds of mixing alone. The following points should be considered when selecting stabilizer: 1 Soluble in water or mixture. 2 can give the mixture good adhesion and foaming. 3 can give the ice cream a good texture and texture. 4 can improve the shape retention of ice cream. 5 has the effect of preventing crystallization from expanding. 6 cheap
1.5 emulsifier
An emulsifier is a substance having a hydrophilic group and a lipophilic group in a molecule, which may be interposed between oil and water so that one side is well dispersed in the middle of the other to form a stable emulsion, and the composition of the ice cream is complicated. The addition of an emulsifier to the mixture has other effects besides emulsification, and can be summarized as follows: (1) The fat globule is in a fine opaque state and stabilized. 2 Disperse and stabilize particles other than fat globules. 3 increase the heat resistance of the ice cream at room temperature. 4 reduce changes in products in storage. 5 Prevent or control the formation of coarse ice crystals, making the ice cream tissue fine. Commonly used emulsifiers in ice cream are glycerate (monoglyceride), sucrose fatty ester (sucrose), polytristearate (Tween), sorbitan fatty acid ester (Span), propylene glycol fatty acid ester (PG). Ester), lecithin, soybean phospholipid, etc. Recently, Taiyuan Rihua has developed triglyceride stearic acid monoglyceride, which is a new type of food emulsifier. The emulsification effect is comparable to molecular distillation monoglyceride, emulsifier. The amount of addition is related to the fat content of the ice cream mix, generally increases with the increase of fat content, and the range is between 0.1% and 0.5%. The performance of the composite emulsifier is better than that of the single emulsifier.
1.6 total solids
The total solid matter is the total of the above-mentioned raw materials, and is a major factor affecting the quality of the ice cream, the expansion ratio, and the like. Those with high solids generally increase the expansion ratio and increase the yield. The structure will become lubricated, the quality will also be improved, and the heat required for freezing and hardening will be improved. However, if the solid content is too high, the viscosity of the mixture is increased to deteriorate the texture, and the cost is also increased. Generally, the solid matter is preferably 25% to 40%.
1.7 spices
Flavors and fragrances can impart an alcoholic aroma to the product and have the natural flavor desired for the variety. The quality of its quality directly affects the quality of ice cream, so when choosing to use, in addition to considering the price factor, the first thing to pay attention to is quality.
2, the impact of ice cream production process conditions
The production process of ice cream must be completed in accordance with certain technical conditions, otherwise it is impossible to produce a product of good quality.
2.1 Inspection of raw materials
The quality of raw materials directly affects the quality of ice cream. Therefore, all kinds of raw materials must be inspected strictly in accordance with quality standards, and those who are not qualified are not allowed to use them. The sensory examination is usually performed first. At the same time, it is tested whether the specific gravity, viscosity, solid content, fat, sugar content, etc. of the raw materials meet the specifications, whether the content of bacteria, arsenic, lead heavy metals, etc. are below the legal standard, and whether the food additives used meet the requirements.
5.2.2 Mixing ingredients
5.2.2.1 Calculation of raw materials
The most basic ingredient for making ice cream is the ingredient, which is the formula calculation. The formula of the ice cream is determined according to the consumer's preference, the price of the raw material and the supply, and the sales status of the product. The quality standard is determined first, and then the mathematical requirements are used to calculate the required amount of various raw materials according to the standard requirements, thereby ensuring that the quality of the manufactured product meets the technical standards. Before the calculation, we must first know the composition of various raw materials and ice cream, as the basis for formula calculation. The formula is calculated by the material balance method. The general calculation of the formula and the amount of each raw material is shown in the production process (3).
2.2.2 Preparation of the mixture
The preparation of the mixture should first weigh the various raw materials according to the proportion of the formula, and then prepare in the batching tank. The order of mixing the raw materials should be started from liquid materials such as low concentration water and milk, followed by liquids such as condensed milk and cream. The raw material is again a solid raw material such as sugar, milk powder, emulsifier and stabilizer. Finally, water, milk and other capacity adjustments. The temperature at which the mixture is dissolved is usually 40 to 50 °C. 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 to dissolve and filter. The ice cream composite emulsion stabilizer can be mixed with the sugar more than 5 times and then added to the mixing tank under constant stirring to fully dissolve and disperse.
2.3 sterilization
The acidity of the mixture and the sterilization method used have a direct impact on the flavor of the product. The acidity of the mixture is preferably 0.18%~0.20% lactic acid. When the acidity is high, it needs to be neutralized with calcium hydroxide or baking soda before sterilization. Otherwise, sterilization will not only cause protein coagulation, but also affect the flavor of the product, but care should be taken to prevent excessive neutralization and astringency during neutralization. The ice cream mixture is heated in a sterilization tank with jacket steam to a temperature of 78 ° C for 30 minutes for sterilization. If continuous pasteurization is used for high temperature instantaneous sterilization (HTST), it is applied at 83~85 ° C for 15 s. Otherwise, high temperature sterilization for a long time will make the product produce cooking taste and burnt smell.
2.4 homogenization
The homogenization of the mixture has an important influence on the shape and structure of the ice cream. Homogenization is generally carried out by a two-stage high-pressure homogenizer. The effect is to make the diameter of the fat globules smaller, generally up to 1~2μm. The same is to increase the viscosity of the mixture to prevent the fat from being stirred into cream particles during freezing. To ensure the fineness of the ice cream product structure, the optimum temperature for homogenization treatment is 65~70°C, the homogenization pressure is 15-20MP for the first stage, the second stage is 2-5MP, and the homogenization pressure is related to the solid content and fat content of the mixture. Increase and decrease.
2.5 cooling, aging
Aging is the refrigerating of the mixture at a low temperature of 2~4 °C for a certain period of time, called "mature" or "maturing". The essence lies in the hydration of fat, protein and stabilizer. The stabilizer fully absorbs the water to increase the viscosity of the liquid, which is beneficial to the increase of the expansion rate during freezing and stirring.
The aging time is related to the temperature of the feed liquid, the composition of the raw materials and the type of the stabilizer, and generally takes 4 to 24 hours at 2 to 4 °C. When aging, care should be taken to avoid contamination of the bacteria. The aging cylinder must be subjected to strict disinfection beforehand to ensure the sanitary quality of the product.
2.6 freezing
In the freezing process, the mixture is frozen under forced stirring, so that the air is evenly distributed in the entire mixture in a very small bubble state, and a part of the water becomes a process of fine crystallization of ice. Its functions are as follows: (1) The ice cream mixture is cooled by the action of the refrigerant, the viscosity is increased, and the thickness is gradually thickened into a semi-solid state, that is, a frozen state. (2) Due to the agitation of the agitator, the scraper continuously scrapes off the material of the barrel wall to prevent the mixed raw material from forming large ice chips on the wall. (3) Due to the constant stirring and cooling of the agitator, the air gradually mixes during the freezing to expand the volume, so that the ice cream reaches a beautiful tissue and a perfect shape.
The freezing temperature is -2~-4°C, the freezing time of the intermittent freezing machine is 15~20 minutes, the discharge temperature of the ice cream is generally -3~ -5°C, the continuous freezing and feeding machine is continuous, and the ice cream discharging temperature is -5~ -6 °C, continuous freezing must always check the expansion rate to control the proper amount of ingress and exit and the air mixed in.
2.7 molding filling
The frozen ice cream must be molded and hardened immediately to meet the needs of storage and sales. The ice cream is formed by various forming filling machines such as anvil, paper cup, egg tube, casting molding, chocolate coated ice cream, shaped ice cream cutting line. It weighs 320 grams, 160 grams, 80 grams, 50 grams, etc., as well as 1 kilogram and 2 kilograms for household use.
2.8 quick freezing, hardening and storage
The ice cream after freezing is soft ice cream without being hardened, and if it is poured into a container and then hardened, it becomes a hard ice cream. The former has many stores available for sale, and the latter has a large output.
The purpose of quick freezing and hardening is to quickly freeze the ice cream (-3~-5°C) from the freezing machine (<-23°C> to freeze the tissue state of the ice cream and complete the formation of very fine ice crystals in the ice cream. To maintain the proper hardness of the tissue, to ensure the quality of the ice cream, easy to sell and store and transport. Quick freezing, hardening can be used in the frozen storage (-23 ~ -25 ° C) or quick-freezing tunnel (-35 ~ -40 ° C). In the quick-frozen training, it is 10~12h. If the quick-freezing tunnel is used, the time will be much shorter, only 30~50 points. The conditions affecting the hardening include the shape and size of the packaging container, the temperature of the freezing room and the circulation state of the air, and indoor products. The location and factors such as the composition and expansion ratio of the ice cream.
Ice cream products after storage and hardening should be stored in a low-temperature refrigerator before sale, and the storage temperature is -20 °C.
3. Impact of ice cream production equipment
The equipment for producing ice cream has a batching cylinder, a sterilization cylinder, a homogenizer, a plate cooler, an aging cylinder, a freezing machine, a filling machine, a quick-freezing library, a refrigerator, etc. according to the process sequence, wherein the most important influence on the quality of the ice cream is sterilization. , homogenizer, freezer, quick-freezer (or quick-freezing tunnel). Practice has shown that it is impossible to produce good ice cream without good equipment.
3.1 sterilizer
The sterilizing equipment of ice cream mixture has various types and structures, and is generally divided into two types: intermittent type and continuous type. The intermittent sterilizer is also called "cold hot and cold tank". The structure is simple, easy to manufacture, convenient to operate and low in price. It is widely used in general cold drink factories. More advanced cold beverage factories use high-temperature short-time pasteurization equipment to automate continuous sterilization of the mixture. The device is mainly composed of four-stage plate heat exchanger, homogenizer, control cabinet, valve and pipeline. . It is characterized by good bactericidal effect, short heating time of the mixture, especially the dairy component is less affected by thermal denaturation, thus ensuring the quality of the product.
3.2 homogenizer
At present, the two-stage high-pressure homogenizer is mostly used, which is composed of a two-stage homogenizing valve and a three-piston reciprocating pump. The ice cream mixture is pulverized by the first-stage homogenizing valve (high-pressure valve) to 1~2μm, and then passed through the second-stage homogenizing valve (low-pressure valve) to achieve the dispersion effect, thereby ensuring that the fat globule in the physical structure of the ice cream reaches The specified size. Make the tissue fine and smooth, so the quality of the homogenizer has a direct impact on the quality of the ice cream.
3.3 freezing machine
The freezing machine is the key mechanical equipment for the finished product of the ice cream. The freezing machine can be classified into an ammonia freezing machine and a Freon freezing machine according to the type of refrigerant used. According to the production mode, it is divided into two types: batch type and continuous type. Continuous type freezer is more commonly used in modern ice cream production. The mixture is pumped in and out at a pressure of 0.15~0.2Mpa, so that low freezing temperature can be used. Freeze more water, make the ice crystal diameter of the product to be 10~5μm, and the diameter of the bubble is about 30~150μm, so as to form a uniform mixture. The ice cream made by the tissue is uniform and finely lubricated, and at the same time, it can be produced. Continuity and efficient production capacity.
3.4 quick freezing library (or quick freezing tunnel)
When the ice cream product leaves the filling machine, its temperature is -3~-5°C, and about 30%~40% of the moisture in the mixture is frozen at this temperature, in order to ensure the stability of the ice cream product and leave it after freezing. Most of the water freezes into tiny ice crystals and is easy to store, transport and sell. The ice cream must be quickly frozen and hardened before being transferred to a cold storage.
The advantages and disadvantages of ice cream hardening have a crucial influence on the final quality of the product. The hardening quickly melts less, the ice crystals in the tissue are fine, and the finished product is finely lubricated. If the hardening is slow, the part is melted, the crystal of ice is large, the finished product is rough, and the quality is inferior. For this reason, more advanced production plants use quick-freezing tunnels. The length of the quick-frozen tunnel is generally 12~15m, the temperature in the tunnel is usually -35~-40°C, and the quick freezing time is 1h. If the ice cream is a small piece that has been dispensed, the temperature of the ice cream after 30~50 minutes on the tunnel Can drop from -5 °C to -18 ~ -20 °C. Due to rapid hardening and low temperature, the shape of the ice cream is stable, the crystal is small, and the texture is fine and smooth.
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