Methods of Pasteurization.There are two basic methods, batch or continuous.
Batch method.The batch method uses a vat pasteurizer which consists of a jacketed vat surrounded by either circulating water, steam or heating coils of water or steam.
In the vat the milk is heated and held throughout the holding period while being agitated. The milk may be cooled in the vat or removed hot after the holding time is completed for every particle. As a modification, the milk may be partially heated in tubular or plate heater before entering the vat. This method has very little use for milk but some use for milk by-products (e.g. creams, chocolate) and special batches. The vat is used extensively in the ice cream industry for mix quality reasons other than microbial reasons.
Continuous Method.Continuous process method has several advantages over the vat method, the most important being time and energy saving. For most continuous processing, a high temperature short time (HTST) pasteurizer is used. The heat treatment is accomplished using a plate heat exchanger. This piece of equipment consists of a stack of corrugated stainless steel plates clamped together in a frame. There are several flow patterns that can be used. Gaskets are used to define the boundaries of the channels and to prevent leakage. The heating medium can be vacuum steam or hot water.
HTST Milk Flow Overview
Cold raw milk at 4° C in a constant level tank is drawn into the regenerator section of pasteurizer. Here it is warmed to approximately 57° C - 68° C by heat given up by hot pasteurized milk flowing in a counter current direction on the opposite side of thin, stainless steel plates. The raw milk, still under suction, passes through a positive displacement timing pump which delivers it under positive pressure through the rest of the HTST system.
The raw milk is forced through the heater section where hot water on opposite sides of the plates heat milk to a temperature of at least 72° C. The milk, at pasteurization temperature and under pressure, flows through the holding tube where it is held for at least 16 sec. The maximum velocity is governed by the speed of the timing pump, diameter and length of the holding tube, and surface friction. After passing temperature sensors of an indicating thermometer and a recorder-controller at the end of the holding tube, milk passes into the flow diversion device (FDD). The FDD assumes a forward-flow position if the milk passes the recorder-controller at the preset cut-in temperature (>72° C). The FDD remains in normal position which is in diverted-flow if milk has not achieved preset cut-in temperature. The improperly heated milk flows through the diverted flow line of the FDD back to the raw milk constant level tank. Properly heated milk flows through the forward flow part of the FDD to the pasteurized milk regenerator section where it gives up heat to the raw product and in turn is cooled to approximately 32° C - 9° C.
The warm milk passes through the cooling section where it is cooled to 4° C or below by coolant on the opposite sides of the thin, stainless steel plates. The cold, pasteurized milk passes through avacuum breaker at least 12 inches ((inch)-дюйм = 2.54 см) above the highest raw milk in the HTST system then on to storage tank filler for packaging. Holding Time
When fluids move through a pipe, either of two distinct types of flow can be observed. The first is known as turbulent flow which occurs at high velocity and in which eddies are present moving in all directions and at all angles to the normal line of flow. The second type is streamline, or laminar flow which occurs at low velocities and shows no eddy currents. The Reynolds number, is used to predict whether laminar or turbulent flow will exist in a pipe:
Re < 2100 laminar
Re > 4000 fully developed turbulent flow
There is an impact of these flow patterns on holding time calculations and the assessment of proper holding tube lengths.
The holding time is determined by timing the interval for an added trace substance (salt) to pass through the holder. The time interval of the fastest particle of milk is desired. Thus the results found with water are converted to the milk flow time by formulation since a pump may not deliver the same amount of milk as it does water.
Questions:
1. What are two distinct purposes for the process of milk pasteurization?
2. What can pasteurization destroy?
3. When is milk deemed pasteurized?
4. What several advantages over the vat method does continuous process method have?
5. Describe high temperature short time (HTST) method?
Lecture # 9. Technology of sour dough. Selection of cultures for dairy production.
1. Selection of sourdough culture for production of dairy products.
2. Classification and characteristics of fermented milk products.
3. Biochemical processes, flowing in the manufacture of fermented milk products
1. Production of various dairy products (fermented milk drink, curd and cheese) is founded on biochemical processes of milk sugar’s fermentation and milk casein’s coagulation. Fermentation of lactose, i.e. turning into connections of less molecular weight, is happened under the influence of lactic-acid, propionate, acetic acid bacteria and yeast.
Lactic acid cocci and rod bacteria belong to lactic acid bacteria, causing lactic-acid fermentation, lactococci and thermophilic streptococcus are included in group of lactic acid cocci, Bulgarian and acidophilic ones are included in group of lactic-acid rod bacteria, as well as rod bacteria, used in cheesemaking.
Propionate bacteria ferment glucose, lactic acid into propionic acid and other matters, which improve taste and smell of product. In the course of multiplication these bacteria can synthesize cyanocobalamin (vitamin B12). Acetic acid bacteria are initiators of acetic-acid fermentation, in consequence of which acetic acid forms.
Clean cultures of lactic acid bacteria and other microorganisms are obtained in special laboratories of pure culture from milk, fine dairy products and plants. For bacterial starters such cultures must be selected, in consequence of which activity high quality dairy products are obtained.
Specialized laboratories and biofactories issue starter cultures depending on their physical state and production methods follow kinds: liquid; dried; frozen; on solid medium. According to number of viable cells and production methods it is distinguished bacterial cultures and bacterial concentrates.
Fermented milk products are divisible into follow groups: fermented milk drink; sour cream; curd; curd product. Fermented milk products are obtained by way of souring of pasteurized, sterilized or melted milk, cream; churn-milk and whey by sour dough, consisting of various lactic acid bacteria, sometimes yeast, and for getting of therapeutic purpose’s products bifidus bacteria are used. For production of fermented milk products also dry, concentrated milk, caseinate, fruit-berrylike and vegetable fillers, sand sugar, flavoring matters, dyes, sweeteners and stabilizers of product’s structure are used. Produce of fermented milk drink is and on the basis of soya bean.
Biochemical processes in the manufacture of fermented milk products. Under action of enzymes, selected by microorganisms, process of deep decomposition of lactose with formation of more simple compounds (lactic acid, alcohol, carbon dioxide) takes place. Depending on formed at fermentation products lactic acid, alcoholic and other fermentation are distinguished.
Lactic-acid fermentation is a basic process in the manufacture of fermented milk product. In the course of lactic-acid fermentation in milk lactic acid accumulates, acidity of milk change. When pH of milk reach 4,6 -4,7; casein loses solubility and coagulate; form clot (сгусток).
At alcoholic fermentation of lactose spirit and carbon form dioxide. In fermented milk products (kefir, kumiss) alcoholic fermentation accompanies lactic-acid fermentation, wherein favourable conditions for yeast growth form. In highest degree alcoholic fermentation develops in kumiss.
By type of fermentation fermented milk products conditionally fall into two classes: resulting from only lactic-acid fermentation and combined - lactic acid and alcoholic fermentation.
In consequence of biochemical processes, flowing at souring milk, fermented milk products acquire dietic and medicinal properties. About dietic and medicinal properties of fermented milk products I. Mechnikov denoted, who consider as premature aging of human organism is due action on him poisonous substances, accumulated in intestinal tract as a result of putrefactive (гнилостные) microorganisms activity. Lactic acid, formed in the course of lactic-acid fermentation, depresses putrefactive microflora and so prevents organism from slow poisoning. I. Mechnikov recommended sour milk (простокваша), produced using Bulgarian rod bacteria, as prophylactic drug from intestinal diseases.
Acidophilous bacterium is firmer to action of alkalies. Acidophilous bacterium possesses a strong antibiotic property in relation to some harmful and pathogenic microorganisms and thus it is used in produce of fermented milk product.
Fermented milk products are more easily digested by organism, than milk. It is explained by milk proteins partially fall into more simple, easy digestible matters. Formed in dietic fermented milk products lactic acid and carbon dioxide influence on secretory activity of the digestive tract, cause more intensive separation of gastric juice and enzymes. At that appetite improves and digestion accelerates. Food is digested with least energy, which is essential at rehabilitation of weakened organisms. Therefore, dietary fermented milk products are used for nutrition of the sick.
2. There exist two methods of fermented milk products production: tank and thermostatic. Tank method (резервуарный способ)of technological process consists of follow technological operation: preproduction of raw material, standardization, homogenization, pasteurization and cooling, addition of starter (заквашивания,), souring (сквашивания) in special reservoirs, clot’s cooling, ageing of clot (kefir, kumiss), prepackaging.
Technological process of fermented milk drinks production by thermostatic method consists of the same process operations, that and in the tank method, realized in such order: preproduction of raw material, standardization, pasteurization, homogenization, cooling to temperature of making sour(заквашивания), addition of starter, prepackaging, souring in thermostatically controlled chamber, cooling of clot, ageing of clot (kefir, kumiss).
3. Technology of sour cream. Sour cream is derived from standardized cream by way of souring of them by sourdough, prepared on clean culture of lactic acid bacteria, and ageing at low temperatures. Depending on microflora of sourdough and weight fraction of fat several-sorted sour cream is produced. Sour cream with weight fraction of fat 10; 15 and 20 % it is possible to produce from mixture of cow cream and soya protein. Mixture is made soured by culture of mesophilic lactic streptococcus. Soya protein is added in cream for improvement of consistence of finished product.
Sour cream is produced by tank and thermostatic method. Milk is centrifuged at 40 -45O C. Gotten cream is standardized by whole or skimmed milk.
Standardized cream is pasteurized at 85- 90O C with holding from 15 sec till 10 min or at 91- 96O C with holding from 20sec till 5min depending on sort of sour cream.
Pasteurized cream is cooled to 60 -70O C and pointed at homogenization. Surface of fat phase in homogenized cream increases. That leads to increase of cream’s viscosity. At that newly formed fat globule membrane additionally connects free water. Protein substances of fat globule membrane take part in structure formation at souring cream. Homogenization improves conditions of milk fat crystallizing at maturity of sour cream, which promotes formation of finished product’s thickness.
Cream after homogenization is cooledto temperature of making sour and made soured by sourdough in quantity 1 5% or bacterial concentrate. Souring of cream flows untill clotting reaction and achievement of necessary acidity. Continuance of souring composes 6 -16 hours depending on sort of sour cream.
At souring, cooling and maturing basic processes of sour cream structure formation, forming consistence of finished product take place. After ending souring cream is mixed and sent on prepackaging. After prepackaging sour cream is sent at cooling and physical ripening. Sour cream is cooled to temperature not above 8O C in cooling chamber (камера) with air temperature 0 -8O C. Synchronous with cooling of product its maturing takes place. Cooling time and ageing in big tare is carried 12 -48 hours, in small tare- 6 12 hours. Ageing is conducted in order to acquire firm texture by sour cream.
Starter Cultures
Starter cultures are those microorganisms that are used in the production of cultured dairy products such as yogurt and cheese. The natural microflora of the milk is either inefficient, uncontrollable, and unpredictable, or is destroyed altogether by the heat treatments given to the milk. A starter culture can provide particular characteristics in a more controlled and predictable fermentation. The primary function of lactic starters is the production of lactic acid from lactose. Other functions of starter cultures may include the following:
· flavour, aroma, and alcohol production
· proteolytic and lipolytic activities
· inhibition of undesirable organisms
There are two groups of lactic starter cultures:
1. simple or defined: single strain, or more than one in which the number is known
2. mixed or compound: more than one strain each providing its own specific characteristics
Starter cultures may be categorized as mesophilic or thermophilic:
Mesophilic
Lactococcus lactis subsp. cremoris
L. delbrueckii subsp. lactis
L. lactis subsp. lactis biovar diacetylactis
Leuconostoc mesenteroides subsp. cremoris
Thermophilic
Streptococcus salivarius subsp. thermophilus (S.thermophilus)
Lactobacillus delbrueckii subsp. bulgaricus
L. delbrueckii subsp. lactis
L. casei
L. helveticus
L. plantarum
Mixtures of mesophilic and thermophilic microorganisms can also be used as in the production of some cheeses.
Starter Culture Preparation
Commercial manufacturers provide starter cultures in lyophilized (freeze-dryed), frozen or spray-dried forms. The dairy product manufacturers need to inoculate the culture into milk or other suitable substrate. There are a number of steps necessary for the propagation of starter culture ready for production:
1. Commercial culture
2. Mother culture - first inoculation; all cultures will originate from this preparation
3. Intermediate culture - in preparation of larger volumes of prepared starter
4. Bulk starter culture - this stage is used in dairy product production
Questions:
1. On what biochemical processes based production of many dairy products (milk drinks, cream, and cheese)?
2. Why are pure cultures of lactic acid bacteria and other micro-organisms (such as yeast) are in special laboratories?
3. How to conduct the selection of individual strains and starter cultures for dairy products?
4. Which method is most common in the production of fermented milk drinks?
Lecture# 10. Technology of sour cream and curd
- Technology of sour cream
- Technology of curd
1. Technology of sour cream.Sour cream prepared from normalized by fermentation of yeast, cooked in pure cultures of lactic acid bacteria and ripening at low temperatures.
Depending on the yeast flora and the mass fraction of fat sour cream is produced in several species.
Sour cream with fat mass fraction of 10, 15 and 20% can be produced from a mixture of cow cream and soy protein. A mixture of fermented cultures of mesophilic lactic streptococci. Soy protein is added to the cream to improve the consistency of the finished product. For the sour cream with fat mass fraction of 10, 15 and 20% mass fraction of soy protein, respectively, 5 ... 6, 4 and 3 ... 2 ... 3 kg to 1000 kg of finished product. Cream with soy protein produce as well as the cream of the cream of the cow. Shelf life of sour cream in a sealed package is 7 days. Under the new standard, the cream can produce a mass of fat content of 10 to 58%.
Sour cream and produce reservoir thermostatic means.
Separating milk at 40 ... 45 ° C. The resulting cream normalize whole or skim milk.
Normalized cream is pasteurized at 85 ... 90 ° C with an exposure of 15 to 10 minutes or 9 ... 96 C with time from 20 seconds to 5 minutes, depending on the type of sour cream.
Pasteurized cream is cooled to 60 ... 70 ° C and sent to homogenization.
In homogenized cream increases the fat phase. This leads to an increase in the viscosity of the cream. In this newly formed membrane of fat globules in addition to bind free water. Proteins fat globule membranes are involved in pattern formation in fermenting cream. Homogenization improves the crystallization of milk fat during the ripening cream, which contributes to a thick consistency of the finished product.
After homogenization, the cream is cooled (and after physical maturation is heated) to the temperature of fermentation and yeast fermented at 1 ... 5% or bacterial concentrate.
Fermentation of cream is to clot formation and reach the required acidity. Duration of fermentation is 6 ... 16 hours, depending on the type of sour cream.
2. Technology of curd
Cottage cheese - dairy protein product, which is produced from normalized pasteurized milk or skim milk, buttermilk and yeast by fermentation followed by removal of the clot from the resulting serum.
The dairy industry produces cheese with fat mass fraction of 18, 9, 5%, and low-fat. Mass fraction of moisture in the finished product, respectively, at 65, 73, 75, and 80%, acidity - 210, 220, 230 and 240 of T. In addition, produce a soft cottage cheese diet with different mass fraction of fat and low-fat, as well as fruit and berry fillers.
Under the new standard, increased the number of cottage cheese on a mass fraction of fat from 1.8 to 23%, with the normalized mass fraction of protein.
To get a bunch of cottage cheese in the technology used acid-rennet and acid coagulation of milk proteins.
There are two ways of making cottage cheese: traditional (normal) and separate.
When fermenting, cooling and maturation processes of structure are basic cream, forming the texture of the finished product.
After the end of ripening cream mixed and sent to the packaging of.
After filling cream direct cooling, and physical maturation. Sour cream is cooled to a temperature no higher than 8 ° C in cold rooms where the temperature is 0 ... 8 ° C. At the same time cooling the product is its maturation. Duration of cooling and maturation in a large container 12 ... 48 hours, and in a shallow 6 ... 12 hours. Maturation of conduct in order to become a dense sour cream consistency.
The traditional way. The technological process of cheese traditionally includes consistently carried out operations: preparation of milk, obtaining raw materials of desired composition, pasteurization, cooling to a temperature of fermentation, fermentation, fermentation, splitting the bunch, whey separation, cooling curd, packing.
Scheme curd production line in the traditional way is shown in Figure 12.
In formulating the cheese with different fat mass fraction is carried by the normalization of milk fat with the mass fraction of protein in whole milk, and for the production of cottage cheese using skim milk.
Raw materials intended for the production of cottage cheese, pre-cleaned.
Pasteurization prepared raw materials is carried out at a temperature of 78 ... 80 ° C with an exposure of 20 ... 30. Pasteurized milk is cooled to a temperature of fermentation, which is in the warm season at 28 ... 30 ° C, and in the cold - 30 ... 32 ° C, and sent to fermentation.
If you use an acid-rennet coagulation of milk proteins, then the fermentation in milk make sourdough, calcium chloride and rennet, if the acid coagulation - the only starter.
Yeast used for fermentation on pure cultures of mesophilic lactococci. Duration of fermentation is 6 ... 8 hours. With accelerated ripening process to make milk ferment, prepared in cultures of mesophilic lactococci and thermophilic cultures of lactic streptococci. Temperature during accelerated ripening process 35 ... 38 ° C, the duration of fermentation 4 ... 4.5 hours.
Calcium chloride needed to restore salt balance disturbed by the pasteurization of milk, bring in a 40% solution of 400 g of anhydrous salt per 1 ton of milk. After that make the milk rennet or pepsin, or an enzyme preparation based on 1t 1g enzyme milk. After making yeast, calcium chloride and rennet milk mixed and allowed to rest until the end of fermentation.
The end of fermentation is judged by the acidity of the bunch. For cottage cheese with fat mass fraction of 18 and 9% acidity should be 58 ... 60 of, for low-fat 66 ... 70 from.
To speed up the release of serum ready clot special wire cutters cut into cubes the size of an edge of about 2 cm Cut clot left alone for 40 ... 60 minutes to separate the serum, and the increasing acidity.
In the production of low-fat cottage cheese using acid coagulation of milk proteins. Obtained in this bunch has less strength than the clot obtained by rennet-acid coagulation, and worse dehydrated. To enhance and accelerate the separation of serum heated received clot ... 38 to 36 ° C with exposure 15 ... 20 min.
Highlight the serum was removed and poured into a clot or coarse calico bags lavsan 7 ... 9 kg and sent for further separation of whey samopressovanie and pressing.
After pressing, the cheese immediately cooled to 3 ... 8 ° C, resulting in lactic fermentation is stopped with the increase of excess acidity. Chilled cheese packed in the form of briquettes in parchment, boxes and cups made of polymeric materials, etc.
Production of cottage cheese in the traditional way using compression bags - tedious and long process. Currently, in order to reduce labor costs and the loss of raw materials, performance and culture as separate operations are mechanized and created mechanized and automated lines.
Separate way. The essence of the method is to separate that first get vysokozhirnye skim milk and cream of fat which is 50 ... 55%. Then of skim milk in a low-fat cottage cheese and mix it with vysokozhirnymi cream.
Low-fat cottage cheese can be made on the equipment used in the traditional way, or mechanized lines.
If the equipment is used, as in the traditional method, the resulting acid-rennet coagulation of low-fat cottage cheese is pressed to the desired moisture content, then is ground to a uniform consistency for rolling, mixed in a kneader with pasteurized and cooled vysokozhirnymi cream and sent for packaging of.
Reservation of cottage cheese. Cottage cheese is a perishable dairy products. In summer cottage produce in larger quantities than in the winter, so the uniform supply of the population proportion of curd reserve. One way to save yogurt for a long time - a freeze. Freezing cheese - is rapid cooling it to set the negative (-25 ° C) temperatures for backup purposes.
Questions:
1. What factors dairy products are beneficial to the digestive organs?
2. How is the sour cream gotten from the normalized cream?
3. Using what processes are basic processes of structure cream, forming the consistency of the finished product?
4. What are consistently carried out manufacturing operations include manufacturing process cheese in the traditional way?
Lecture # 11,12. Technology of canned and dry milk.
1. Theoretical basis of conservation of milk.
2. Classification of preserved milk products.
3. Requirements to quality of raw material for preserved milk products, evaluation test of raw material.
4. Main methods of drying of dairy products: spray-type, contact, sublimate.
1. Theoretical basis of conservation of milk.
Canned milk is product, produced from liquid milk using condensation and drying. They have high energy value owing to concentration in them of milk ingredients. Therewith, canned milk is characterized by good transportability and considerable shelf stability.
Conservation is processing food by special method in aid of prevention them from spoiling. Main cause of quality changes of products on keeping is action of microorganisms. Therefore among all of conservation’s methods method, directed on destruction of microorganisms, or on inhibition of their activity is the major. In consequence of conservation product gains the capacity to be stored at a long time. Among of all the known principle conservation for production canned milk uses two: abiosis and anabiosis.
Abiosis. Conservation on the principle of abiosis is founded on complete destroy of microorganisms in product (sterilization). In the manufacture of canned milk heat sterilization is used, which is realized under action of high temperatures, as a result of which not only vegetative, but and spore forms of microorganisms perish. Received in such manner milk holds long-time storage.
Anabiosis. Conservation on the principle of anabiosis consists in suppression of microbiological process by chemical or physical means. In the manufacture of canned milk only physical means: rise osmotic (osmoanabiosis) and drying-up (xeroanabiosis) are used.
Conservation by raise of osmotic pressure is founded on breakdown natural metabolism between alive cells and medium.
Osmotic pressure in milk composes 0, 74 MPa. Microorganisms, intracellular pressure of which composes 0,4- 0,6 MPa, entering milk, because of minor difference in pressure in conditions of sufficient amount of moisture and nutritive substances nicely advance in it, which cause spoiling of product. Raise of osmotic pressure in milk is possible by way of increase of milk-solids content by condensation of milk and dissolving of sugar in it. In condensed milk osmotic pressure achieves 18 MPa. Such sudden rise in comparison with initial creates conditions, negative for microorganisms’ activity.
Conservation by drying is founded on removal from product moisture and creation of physiological dryness, causing increase of the difference between osmotic pressure in bacterial cell and environmental pressure.
For normal behavior of process, connected with activity microorganisms, it is necessary that water content; mass % in product composes about 25- 30 %. Therefore, if moisture content in product is less of minimum, required for microorganisms’ activity, firmness of product on keeping heightens. Weight fraction of moisture in powdered milk composes 3 -4%. To inhibit development of residual microflora, dried product is necessary to prevent from moisture absorption.
2. Classification of preserved milk products. Classification of canned milk depending on conservation method is shown in the follow table 11.1.
Table 11.1 - Classification of canned milk depending on conservation method
| Conservation’s principle | Conservation method | Canned milk |
| Абиоз Anabiosis: osmoanabiosis xeroanabiosis | Heat sterilization Condensation Drying | Sterilized condensed milk Sterilized concentrated milk. Sterilized cream. Condensed with sugar whole milk Condensed with sugar cream. Preserves with condensed milk, sugar and fillers (coffee, cacao) Cow whole milk powder. Cow skim dried milk. Dry cream. |
Sterilized condensed and concentrated milk Depending on content of solid matters two kind of sugarless preserves are produced: condensed sterilized milk and concentrated sterilized milk with high concentration of solids.
Mass fraction of solids in condensed sterilized whole milk should be at least 25.5%, including the fat mass fraction of at least 7.8%, and in concentrated sterilized milk solids mass fraction of at least 27.5%, including fat not less than 8.6%.
Technological process of production of condensed sterilized milk and concentrated sterilized milk, consist of following operations: receipt and preparation of milk, standardization, heat treatment and condensation, homogenization and cooling, standardization, addition of stabilizer salt, prepackaging, sterilization, keeping.
Peculiarity of technological process at production of condensed sterilized canned milk is sterilization of product, therefore for manufacture of sterilized preserves milk not low of I grade, acidity not above 19OT and thermal stability on alcoholic test not low of IV group and 18 OT with thermal stability not low of III group and with low bacterial content is usable.
The canning methods are based on moisture removing. Moisture is the necessary component for growth of micro flora. There are condensed and dry milk produced as canned milk.
Condensed milk is produced from full-cream or skimmed milk by evaporation. If condensed milk is produced without sugar, osmosis pressure won't promote a suppression* of microorganisms vital functions and ferments inactivation. In this case the condensed milk is sterilized.
Technological process of condensed milk
milk reception
 |
purification
normalization
 |
pasteurization
 |
condensation by evaporation
Then the process can be carried out in two directions.
1. Condensed milk with sugar: addition of sugar syrup at the evaporation, cooling and crystallization of sugar, packing.
2. Condensed milk without sugar: homogenization, packing, sterilization.
If condensed milk with sugar is produced, at evaporation of milk sugar syrup will be added with concentration of dry substances 70-75 % to it.
The condensed milk with sugar is packed into hermetical tins or into the wooden* or plywood* barrels* and stored at temperature no more than +10 0С and air relative humidity not more than 75 %.
At producing condensed milk without sugar after evaporation it is homogenized and sterilized, gradually raising temperature up to 117 0С and is held during 15 minutes. As stabilizers of proteins disodic phosphate, sodium citrate, sodium carbonate etc are added to milk.
The condensed milk without sugar is packed into hermetical tin jars and stored at the temperature 0-10 0С and air relative humidity not more 85% during 12 months.
3. Chosen for the quality and refined milk normalized to a mass fraction of fat and SNF.
Normalized formula milk prior to pasteurization necessarily tested for heat resistance as well as the production of sterilized canned milk is exposed to high temperature and low temperature resistance can occur coagulation, flocculation and thickening of the finished product. Heat stability of milk is highly dependent on its chemical composition and, especially, from the equilibrium of the salt composition.
Increase heat stability of milk is achieved making salt-stabilizers. They are added to a mixture of pasteurized or evaporated milk.
To develop sterilized condensed canned milk in the country are widely used in the sterilization container.
To develop sterilized condensed canned milk in the country are widely used in the sterilization container.
Condensed or evaporated milk, has stood trial sterilized, filled into pre-washed and steamed cans. Filled and packed banks check for leaks and sent for sterilization. To sterilize the product in the container using a continuous hydrostatic sterilizers or rotary type, and batch sterilizers. In hydrostatic sterilizers such banks with condensed or concentrated milk is sterilized at a temperature of 116 ... 117 ° C with time 15 ... 17 min. In devices batch sterilization is carried out at a temperature of 116 ... 118oS delayed 14 ... 17 min. Cooling temperature sterilized canned should be 20 ... 40 C. Finished products are stored at a temperature of 0 to 10 ° C and relative humidity up to 85% for up to 12 months from the date of manufacture.
In the production of sterilized canned in winter and spring, the purged often thicken and deteriorate due to the low thermal stability of milk, even with the addition of salt-stabilizers. To prevent contamination of canned milk cooked them carried out at lower temperatures and exposure due to the addition of antibiotic nisin. It is known that nisin, being harmless to humans and animals, causing the death of vegetative and spore forms of bacteria. Reducing the temperature sterilization up to 112 ... 115 ° C (instead of 118 ° C) and exposure to 12 min for nisin positive effect on the quality of the finished product. In condensed sterilized milk with nisin for 30% reduced viscosity and acidity of the product, there is no taste of caramelization.
Sweetened condensed milk
The product is produced from pasteurized cow's milk using a thickening and adding sugar to control the growth of microorganisms. Organoleptic finished product has a clean, sweet taste with no off-flavors and odors, smooth consistency without the presence of sugar crystals, perceptible to the taste. On the chemical composition in condensed whole milk with sugar mass fraction of moisture is not more than 26.5% sucrose - at least 43.5, the total mass fraction of solids 0 28.5, including fat - not less than 8.5%.
The technological process of sweetened condensed milk is carried out in the following sequence: acceptance, training and back-up material, normalization, homogenization and pasteurization, preparation and administration of liquid sugar, thickening, cooling, packing and storage.
Preparation of sugar syrup. Pre-cleaned with a sieve sugar dissolved in hot water (70 ... 80 ° C), then the syrup to boil without delay to ensure its sterility. At temperatures above 100 ° C in syrup possible inversion of sucrose, which is the product of hydrolysis of invert sugar. To avoid the inversion of sugar syrup excerpt from the beginning of the boil before mixing it with the milk must not be more than 20 minutes. Before mixing with the milk sugar syrup is filtered through a filter or a centrifuge. Condensed milk-sugar mixture is completed when the mass fraction of water 29 ... 31% with the additional moisture evaporation in a vacuum cooler.
The crystallization of lactose. In the condensed milk with sugar lactose mass fraction is 11.4%, or 0.44 kg per 1 kg of water. The solubility of lactose in pure water is: at 60 ° C - 0.587 kg / kg of water at 40 ° C - 0, 326 kg / kg of water at 20 ° C - 0.192 kg / kg of water.
Sucrose present in the condensed milk cans in the ratio of lactose 4: 1, reduces the solubility of lactose is almost 1.5 times. Consequently, at 40 ... 60 ° C, and even more so at 20 ° lactose is in a supersaturated state and is able to crystallize.
Cooling of sweetened condensed milk is accompanied by an increase in viscosity of the product in 2 ... 3 times and crystallization of lactose. Crystallization is because when the temperature decreases and the solubility of lactose obtained supersaturated solutions, which forms the center of crystallization.
Sweetened condensed milk is cooled to 20 ° C and sent to the consumer packaging or shipping container. The finished product is stored at a temperature between 0 and 10 ° C and a relative humidity of 85% at 12 months.
At selection of raw milk for preserves chemical composition and properties must be taken into account. Water content, mass % in milk must compose 87,5%, fat -4,0%, nonfat milk solids (SOMO)- 8,75%. At that attitude of fat to nonfat milk solids must be to the extent of 0,4…0,69.To raw material, for production of canned milk, exclusive standards put forward, because diseases of raw milk in consequence of concentration solids strengthen.
4. Main methods of drying of dairy products: spray-type, contact, sublimate.
Whole milk powder
Technological process of production of whole milk powder comprises the steps of acceptance to the condensed milk, which are common to the production of canned milk. They have already been considered, so let's have a very short, and more - on the characteristics of homogenization and drying of milk.
In the production of milk powder normalized to fat and dry matter of the milk is pasteurized at a temperature of not less than 90 °. Standardized milk to thicken the use of multi-vacuum evaporators operating as falling film or circulation systems.
The need to homogenize condensed milk due to the fact that the mechanical, thermal processing and thickening occurs destabilization of fat fraction of milk (fat free selection), promotes fat oxidation and spoilage during storage. Therefore, to increase stability and reduce the content of free fat milk is homogenized. Homogenization is carried out at a temperature of 50 ... 60 ° C and a pressure of 10 ... 15 MPa for single-stage homogenizer, for a two-stage homogenizer - at pressure 11.5 ... 12.5 MPa in the first stage and 2.5 ... 3.0 MPa at the second. After homogenization, the condensed milk enters the intermediate tank and then dried.
In the dry whole milk fat mass fraction is 20 ... 25% and moisture to 4 ... 7%. Based on the composition of milk powder can be concluded that it is not completely dry, it contains a so-called non-removable moisture. As drying the remaining moisture in the product all firmly held there by increasing the cohesive forces of increasing resistance to water movement. Therefore, the product can be dried only to the equilibrium moisture content corresponding to the relative humidity and temperature of the drying agent.
Depending on the method of removing moisture use different drying methods: film (pin), spray (air) and sublimation.
The dry milk is produced from full-cream or skimmed milk by drying up to residual humidity of 3.5%.
Technological process of dry milk includes the following operations: milk reception, purification, normalization, condensation by evaporation (drying on cylinder drier or a spray-type drier), removal of a formed firm, crushing, and packing.
To produce instant dry milk it (that is dry milk) is humidified up to the content of moisture 10% and repeatedly dried up.
Questions:
1. What product made from natural milk with the use of condensation (followed by sterilization or sugar) and drying you know?
2. What is the basis for the principle of preserving abioz?
3. Principle on which the preservation is to suppress microbiological processes by chemical or physical means?
4. On what is canning by drying based?
5. Why to raw materials intended for the production of canned milk, more demanding?
Lecture #13,14
1. Technology of butter.
2. Influence of production methods and compound on the structure, properties and quality of butter.
3. Technology of ice cream
1. Technology of butter. Characteristics of butter. Butter is foodstuff, produced from cow milk, consisting mainly from milk fat and plasma, wherein all milk ingredients: phosphatides, proteins, lactose, mineral substance, skin factor water move partially.
Flavour and smell of dairy butter is specified by presence therein matters, one part of which passes into it from initial milk and cream, but other part (major) develops in consequence of heat treatment, physical and biological maturating and others. Gustatory component of dairy butter are diacetyl, volatile fatty acids, some ethers of fatty acids, lecithin, protein, fats and lactic acid.
Yellow colour of dairy butter is given by beta-carotene. Depending on content of carotin butter has rich colour with buff-colored tinge or straw-coloured tinge, and sometimes it is almost white. Nutritive value of dairy butter defines by its chemical compound: milk fat, fatty acids, phospholipids, mineral substance, vitamins and others.
Milk fat makes up the human body energy expenditure. Energy value of the traditional butter with fat mass fraction of 82.5% of 31 130 kJ / kg, very low fat butter "Edelweiss" - 21100 kJ / kg, Oil Filled - 2081 ... 3113 kJ / kg.
Digestibility of dairy butter composes 97- 98 %. Low temperature of melting of glycerides’ basic groups (27…34 оС) and solidification (18…23 оС) promotes transition of milk fat in digestive tract in right for assimilation liquid state. In connection with this dairy butter is recommended to sick with functional disorder of digestive organs, as well as for infant food.
Methods of butter production. Technological process of butter manufacture includes concentration of fat milk, breaking of fat emulsion and formation of tailor-made product’s structure. Two methods of butter production differ: creaming (cream churning) and transforming of high-fat cream. At production of butter by churning method concentrating of fat phase is achieved by skimming and subsequent breaking of milk fat emulsion at churning of received cream. Moisture content is regulated during butter treatment. Crystallization of milk fat glycerides ends during physical ripening before mechanical treatment of butter.
For getting butter by transforming of high-fat cream concentrating of milk fat phase is carried out by skimming. Standardization of high-fat cream by moisture is conducted to beginning of thermo mechanical treatment with such account, that weight fraction of fat in cream corresponds weight fraction of fat in finished product. Breaking of fat cream emulsion and crystallizing of milk fat’s glycerides happen mainly during thermo mechanical treatment.
For production of butter by the listed ways, there are various production lines.
Lines for the process in one or other way have pecular equipment. For example, in-line production of butter by churning process includes tank for physical ripening of cream, which is not in the line of production of butter by the way of high fat cream transforming. In the same line buttermaking machine of continuous or periodical action are included. In the production line of butter by the way of high fat cream transforming there are included high fat cream separators for high fat cream, which are absent in the butter production line by the churning way. These lines are supported by butter formers of different types and designs: cylindrical (three-, four-cylinder) and plate for the conversion of high fat cream into butter.
Technology of butter by cream churning.
This method involves the following sequence of the operations: milk reception, cooling, storage, heating, separation of milk, cooking cream, low temperature of their training (physical maturation cream), whipping cream, wash butter grains, salting butter (for salt butter), mechanical processing, packing and storage of butter.
Way for the development of butter churning buttermaking machine in continuous use cream with fat mass fraction of 36 ... 50%. Such a concentration of fat accelerates buttermaking machine. In formulating the butter way buttermaking machine churning in batch using medium butter cream with fat mass fraction of 32 ... 37%.
2. Low-temperature treatment of cream
After cooking cream is quickly cooled to a temperature below the solidification of milk fat and maintain a certain time (physical maturation).
As a result of physical maturity cream hardens inside fat milk fat globules, altered state of the shell and the properties of the fat globules of cream: the stability of emulsion and dispersion of oil, the viscosity of the cream.
Solidification of milk fat - the main purpose of low-temperature treatment of cream, it plays an important role in the process masloobrazovaniya. Only in the presence of solidified fat with creaming butter fat can be identified in the form of grain and oil to ensure a good consistency of butter and fat in the normal waste buttermilk.
State membranes of fat globules in cream ripening changes significantly. Some substances membrane of fat globules, in particular phospholipids, moving into the plasma. Fat globule membranes become thinner and more fragile and easily destroyed by creaming in oil.
Appearance of crystals of milk fat in the fat globules violates connection between fat and fat globule membranes, which leads to a decrease in the stability of emulsion fat in the cream.
In the crystallization of milk fat during physical ripening cream in mainly two groups of mixed crystals: low-melting, melting point 15 ... 25 ° C and high melting melting at 27 ... 35 °. To get a good consistency oil ratio and high melting fusible groups of crystals should be 2:1. To this end, control the temperature of ripening cream. If the fat is dominated by low-melting glycerides (spring and summer), the maturation of the cream is carried out at lower temperatures than fat dominated high melting glycerides (autumn-winter period).
The essence of creaming is to destroy the membranes and aggregation (clumping) of fat globules, resulted in the formation of oil seeds.
Factors affecting the creaming. Churning cream into butter - a complex process, it depends on many factors, which indicate the following: the frequency of rotation of the body buttermaking machine, the initial temperature whipping cream, cream and other fat.
Butter granules washing.
To create conditions unfavorable for the growth of microorganisms in butter, it is performed the cleaning of butter granules, during which part of the plasma is removed, along with water, thereby reducing the nutrient content, but resistance of the butter storage increases.
Flushing can influence the consistency of butter. To correct the consistency of butter granules, used for flushing water. The water temperature should correspond to the temperature buttermilk, when the consistency of butte granules is normal. When washing the soft granules temperature of the water is reduced by 1 ... 2 °. The water temperature for washing coarse, crumbled butter granules should be 1 ... 2 ° C above the temperature of the buttermilk.
Salting butter
Salting gives oil moderately salty flavor and increases the resistance of the oil in storage. Dissolved in the plasma of oil, salt increases the osmotic pressure, so that stops the development of microorganisms in oil. To stop the development of all types of bacteria, mold and yeast mass fraction of salt in the butter should be at least 4%, but in this case the oil would sharply salty taste, so the standard provides the mass fraction of salt in the oil no more than 1.5%.Механическая обработка масла
Mechanical treatment is used to form from isolated granulas of the solid butter layer, control of moisture content in accordance with the requirements of the standard, uniform distribution and dispersion of moisture and getting required structure and consistency of butter.
Unsalted butter is immediately treated after the washing process, and salted butter - after salting or parallel to it.
Mechanical treatment process in continuous buttermaking machines can be divided into three stages.
In the first stage separate butter granules are gradually joined in a continuous friable layer. At this stage, moisture is removed from the butter granules and partially - mechanically bound moisture in the microcapillaries. After a while, moisture squeezing from the butter layer stops. The time of processing, corresponding to low moisture content in the butter, called critical, which corresponds to a mass fraction of moisture in butter 11%. At the critical moment the moisture is separated and absorbed in the equal amounts.
In the second stage the butter is able to retain moisture, at that more moisture is absorbed in the butter than squeezed out of it. In the second stage, dispersion of large drops of moisture and its uniform distribution in the amount of butter occur and capillary moisture is encapsulated, then partial destruction of the structure, which was formed in the first stage occur.
In the third stage of processing the moisture content of butter increases and almost completely squeezing stops, while dispersion of plasma drops and their uniform distribution is continuing. The third stage ends after ending mechanical impact. The structure of the butter should be homogeneous and plastic.