A method for freezing raw milk, a thawing method for thawing the frozen raw milk, and application thereof

Abstract

This invention belongs to the field of raw milk cryopreservation and dairy product preparation technology, specifically relating to a method for freezing raw milk, a method for thawing frozen raw milk, and their applications. This invention concentrates raw milk, forms a liquid layer on the wall of a freezing chamber drum, and rapidly freezes it. This layer is then removed by a stirring scraper, reducing the problem of large ice crystals and uneven freezing of different components. This rapid, thin-ice freezing method reduces the formation of large ice crystals, ensuring that the ice crystal particle size remains relatively uniform. This reduces the damage to proteins and fats in milk caused by freezing, solving the problem of protein instability and damage to milk fat structure caused by large ice crystals formed in traditional freezing methods, which easily lead to stratification and precipitation after thawing and subsequent processing. It also solves the problems of long thawing times and uneven concentrations of different components in milk caused by traditional freezing methods.

Description

Technical Field

[0001] This invention belongs to the field of raw milk freezing and dairy product preparation technology, specifically relating to a method for freezing raw milk, a method for thawing frozen raw milk, and their applications. Background Technology

[0002] Raw milk is the primary raw material for dairy processing. However, the long transportation distance from farms to factories increases the risk of quality changes and the proliferation of psychrophilic bacteria during transport. Furthermore, raw milk production is significantly affected by the seasons, often manifesting as follows: In summer, reduced milk production leads to insufficient raw milk supply, yet summer is also the peak season for dairy consumption. Conversely, as temperatures drop, milk production peaks during the off-season, resulting in a surplus of raw milk. To address this imbalance, raw milk is typically spray-dried into milk powder for reconstitution. However, the spray-drying process denatures proteins and oxidizes fats, resulting in some defects in taste and flavor when the milk powder is reconstituted. Currently, the price of domestically produced spray-dried milk powder is significantly higher than that of imported milk powder, putting pressure on dairy companies' costs due to this price inversion.

[0003] Freezing, as an effective preservation method, is widely used in the food processing industry. Freezing extends the shelf life of food by lowering the temperature of the object being preserved, thereby slowing down or reducing biological, physical, and chemical changes that occur during storage. However, during the freezing process of milk, the freezing rate and temperature affect the thawing process, leading to dehydration and solid-liquid separation, thus reducing food quality. In particular, during the freezing of raw milk, the different freezing rates of different components and the formation of ice crystals and lactose crystals cause a certain degree of protein denaturation. This results in different concentrations of protein, fat, and carbohydrates at different locations, as well as precipitation and stratification, when thawed using traditional methods. Although deep freezing (-80℃ and below) of food for a short period combined with low-temperature thawing can solve this problem to some extent, the economic cost is high, making it unsuitable for high-volume, low-value-added food processing industries. Summary of the Invention

[0004] The purpose of this invention is to provide a freezing method for raw milk, a thawing method for frozen raw milk, and their applications. The freezing method can reduce the damage to proteins and fats in milk caused by freezing. Combined with the thawing method, it can effectively ensure the quality of thawed frozen raw milk, extend the shelf life of raw milk, improve the problem of poor condition of milk after freezing, reduce the impact on the use and taste of subsequent processed products, and is both convenient and economical to operate.

[0005] This invention provides a method for freezing raw milk, comprising the following steps:

[0006] Fresh milk is concentrated to obtain concentrated fresh milk;

[0007] The concentrated raw milk is injected into a freezer chamber with a rotating drum for freezing. During the freezing process, a stirring scraper connected to the inner wall of the rotating drum is used to scrape off the formed frozen liquid layer to obtain frozen milk paste.

[0008] The frozen milk is filled into a storage container and quick-frozen to obtain frozen raw milk.

[0009] Preferably, the freezing and scraping are performed under vacuum conditions, wherein the vacuum degree is 0.01 to 0.08 MPa.

[0010] Preferably, the concentration method includes vacuum falling membrane concentration, reverse osmosis concentration, or ultrafiltration concentration; the concentrated raw milk has a protein content of 3.5% to 10%, a fat content of 3.8% to 13.5%, and a lactose content of 4.6% to 5.5%.

[0011] Preferably, the rotational speed of the rotating drum is 40–100 rpm; the temperature in the freezing chamber with the rotating drum is -25 to -10°C, and the outlet temperature is… -2～-8 ℃ ； The thickness of the liquid freezing layer is 0.1 to 3 mm.

[0012] Preferably, the distance between the edge of the stirring scraper and the inner wall of the rotating drum is 0.1–5 mm, and the angle is 10–30°; the rotation speed of the stirring scraper is 30–150 rpm; and the temperature of the stirring scraper and the rotating drum are kept consistent.

[0013] Preferably, the quick-freezing method includes air-cooled quick-freezing, and the quick-freezing temperature is not lower than -18°C.

[0014] The present invention also provides frozen raw milk obtained by the freezing method described in the above technical solution.

[0015] The present invention also provides a method for refreezing and thawing frozen raw milk as described in the above technical solution, comprising the following steps:

[0016] The frozen raw milk is unmolded, and the unmolded frozen raw milk is subjected to ice slurry treatment to obtain raw milk ice slurry.

[0017] The raw milk ice slurry is heated to 4-6°C to obtain thawed reconstituted milk.

[0018] Preferably, the demolding method includes low-temperature demolding, room-temperature demolding, or hot demolding; the temperature of low-temperature demolding is not higher than 10°C; and the temperature of hot demolding is 60-80°C.

[0019] The present invention also provides the application of the freezing method or the reconstitution and thawing method described in the above technical solutions in the production of dairy products.

[0020] Beneficial effects:

[0021] This invention provides a method for freezing raw milk, comprising the following steps: concentrating raw milk to obtain concentrated raw milk; injecting the concentrated raw milk into a freezing chamber equipped with a rotating drum for freezing, while simultaneously scraping off the formed liquid frozen layer with a stirring scraper connected to the inner wall of the rotating drum to obtain frozen milk paste; and filling the frozen milk paste into a storage container for quick freezing to obtain frozen raw milk. This invention concentrates raw milk, forming a liquid layer on the rotating drum wall of the freezing chamber and rapidly freezing it, which is then scraped off by the stirring scraper. This reduces the problems of large ice crystals and uneven freezing of different components. This rapid, thin-ice freezing method reduces the formation of large ice crystals, ensuring that the ice crystal particle size remains relatively uniform, reducing the damage to proteins and fats in milk caused by freezing. It solves the problem that large ice crystals formed by traditional freezing methods lead to protein instability and damage to the milk fat structure, resulting in easy stratification and sedimentation after thawing. It also solves the problems of long thawing times and uneven concentrations of different components in milk caused by traditional freezing methods.

[0022] Based on this, the present invention also provides a method for refreezing and thawing frozen raw milk as described in the above technical solution, comprising the following steps: unmolding the frozen raw milk; subjecting the unmolded frozen raw milk to ice slurry treatment to obtain raw milk ice slurry; and heating the raw milk ice slurry to 4-6°C to obtain thawed refreezed milk. This refreezing and thawing method can achieve rapid thawing of frozen raw milk, effectively ensuring the quality of the refreezed frozen raw milk, extending the shelf life of the frozen raw milk, and is convenient and economical to operate. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0024] Figure 1 This is a photograph of the frozen milk paste prepared by the freezing method of the present invention.

[0025] Figure 2 This is a photograph of frozen raw milk prepared by the freezing method of the present invention.

[0026] Figure 3 The reconstituted milk obtained after thawing using the reconstitution thawing method of the present invention;

[0027] Figure 4 This is a diagram showing the relative relationship between the stirring scraper and the inner wall of the rotating drum in this invention. Detailed Implementation

[0028] This invention provides a method for freezing raw milk, comprising the following steps:

[0029] Fresh milk is concentrated to obtain concentrated fresh milk;

[0030] The concentrated raw milk is injected into a freezer chamber with a rotating drum for freezing. During the freezing process, a stirring scraper connected to the inner wall of the rotating drum is used to scrape off the formed frozen liquid layer to obtain frozen milk paste.

[0031] The frozen milk is filled into a storage container and quick-frozen to obtain frozen raw milk.

[0032] This invention concentrates raw milk to obtain concentrated raw milk. The raw milk used in this invention preferably includes, but is not limited to, raw cow's milk, pasteurized milk, or whole or skim milk prepared by other sterilization methods. The raw milk used in this invention is preferably raw cow's milk that meets national standards, and the total bacterial count of the raw cow's milk is preferably less than 1 × 10⁻⁶. 4 cfu / mL, somatic cell count preferably less than 2×10 5 The concentration ratio is approximately 3.1% per mL; the protein content is preferably not less than 3.1%, and the fat content is preferably not less than 3.4%. The concentration method of this invention preferably includes vacuum falling membrane concentration, reverse osmosis concentration, or ultrafiltration concentration, more preferably reverse osmosis concentration or ultrafiltration concentration; the concentration temperature is preferably 4–6°C; the concentrated raw milk obtained after the concentration method preferably has a protein content of 3.5%–10%, a fat content of 3.8%–13.5%, and a lactose content of 4.6%–5.5%. The concentration method can remove some of the water from the milk, reducing subsequent transportation and storage costs.

[0033] After obtaining the concentrated raw milk, the present invention injects the concentrated raw milk into a freezing chamber equipped with a rotating drum for freezing. A stirring scraper connected to the inner wall of the rotating drum scrapes off the formed frozen liquid layer to obtain frozen milk paste. Preferably, the concentrated raw milk is injected into the freezing chamber with a rotating drum using a centrifugal pump under stirring conditions. The raw milk in the present invention is preferably in a stirred state after concentration, that is, stirred after concentration and injected into the freezing chamber with a rotating drum under stirring conditions. The stirring speed is preferably 40–100 rpm, more preferably 60–80 rpm.

[0034] The concentrated raw milk of this invention is preferably injected tangentially into the freezing chamber with a rotating drum. The temperature of the freezing chamber with the rotating drum is preferably -25 to -10°C, more preferably -20 to -18°C. The temperature of the freezing chamber with the rotating drum is set by a freezing medium located in a jacket outside the rotating drum and flowing within the jacket. The thickness of the liquid freezing layer is preferably 0.1 to 3 mm. The rotation speed of the rotating drum is preferably 60 to 120 rpm, more preferably 100 rpm.

[0035] In this invention, after the concentrated raw milk forms a liquid frozen layer on the inner wall of the rotating drum, a stirring scraper connected to the inner wall of the rotating drum scrapes off the liquid frozen layer to obtain frozen milk paste. Preferably, the scraping is performed simultaneously with the freezing. The distance between the edge of the stirring scraper and the inner wall of the rotating drum is preferably 0.1–5 mm, more preferably 0.2–3 mm, and even more preferably 0.3–2.5 mm. The distance between the edge of the stirring scraper and the inner wall of the rotating drum can preferably be adjusted by manually replacing the scraper before the scraping operation, or by hydraulically adjusting the distance between the stirring scraper and the inner wall of the rotating drum. The angle between the stirring scraper and the inner wall of the rotating drum is preferably 10–30°, and the relative relationship between the stirring scraper and the inner wall of the rotating drum is as follows: Figure 4 As shown; the preferred process for adjusting the distance between the stirring scraper and the inner wall of the rotating drum via hydraulic means is as follows: by adjusting the pressure of compressed air in the hydraulic linkage cavity, the opening angle of the stirring scraper is controlled, thereby adjusting the distance between the edge of the stirring scraper and the drum wall; the rotation speed of the stirring scraper is preferably 30-150 rpm, more preferably 60-80 rpm. The stirring scraper of the present invention preferably has temperature control, maintaining the temperature of the stirring scraper during operation consistent with the temperature of the freezing chamber, reducing the temperature difference between the stirring scraper and the frozen milk layer during stirring, thus affecting the scraping effect. To reduce air contamination, the freezing chamber of the present invention preferably maintains a vacuum, preferably 0.01-0.08 MPa, more preferably 0.04-0.06 MPa, which can preferably be achieved using conventional vacuum equipment. The outlet temperature of the freezing chamber with rotating drum of the present invention is preferably -8 to -2℃, more preferably -5 to -2℃; this outlet temperature ensures that the frozen milk has a certain fluidity, facilitating the transfer of the frozen milk into the storage container. Figure 1 This is a picture of the obtained frozen milk mixture.

[0036] After obtaining the frozen milk paste, the present invention fills the frozen milk paste into a storage container for quick freezing to obtain frozen raw milk. A physical image of the frozen raw milk of the present invention is shown below. Figure 2As shown. The storage container of the present invention preferably includes a plastic bag or an iron drum; the quick-freezing method preferably includes air-cooled quick-freezing, and the quick-freezing temperature is preferably not lower than -18°C.

[0037] Compared with traditional freezing methods, the freezing method described in this invention reduces the formation of large ice crystals, resulting in more uniform ice crystal particle size. This reduces the impact of freezing on the physicochemical properties of raw milk, making the finished product less prone to stratification and sedimentation, and extending its shelf life. Based on these advantages, the frozen raw milk obtained by the freezing method described in the above-mentioned technical solution also falls within the scope of protection of this invention.

[0038] The present invention also provides a method for refreezing and thawing frozen raw milk as described in the above technical solution, comprising the following steps:

[0039] The frozen raw milk is unmolded, and the unmolded frozen raw milk is subjected to ice slurry treatment to obtain raw milk ice slurry.

[0040] The raw milk ice slurry is heated to 4-6°C to obtain thawed reconstituted milk.

[0041] This invention involves unmolding the frozen raw milk to obtain unmolded frozen raw milk. The unmolding method preferably includes low-temperature unmolding, room-temperature unmolding, or hot unmolding, more preferably low-temperature unmolding or hot unmolding; the temperature for low-temperature unmolding is preferably not higher than 10°C; the temperature for hot unmolding is preferably 60–80°C; and the hot unmolding is preferably performed in a hot air tunnel. The unmolding time is preferably not more than 5 hours, more preferably 0.1–0.5 hours.

[0042] After obtaining the unmolded frozen raw milk, the present invention performs an ice-slurry treatment on the unmolded frozen raw milk to obtain raw milk ice slurry. Preferably, the unmolded frozen raw milk is poured into a homogenizer for the ice-slurry treatment, and the ice slurry is in a flowable mud-like state, with a preferred temperature of -4 to -2°C.

[0043] Before the ice-slurry treatment, the present invention preferably further includes placing the unmolded frozen raw milk in an ice crusher equipped with ice claws for crushing, and then subjecting the resulting crushed milk blocks to the subsequent ice-slurry treatment. The volume of the crushed milk blocks in the present invention is preferably 10cm × 5cm × 5cm.

[0044] After obtaining the raw milk ice slurry, the present invention heats the raw milk ice slurry to 4-6°C to obtain thawed reconstituted milk. The thawed milk can be used directly or after processing with the addition of water or other ingredients. A physical image of the thawed reconstituted milk prepared by the present invention is shown below. Figure 3As shown. The present invention preferably uses a heat exchanger for the heating process, and the heat source is preferably waste heat generated during dairy processing, in order to fully utilize the excess heat source and reduce energy costs. During the heating process, stirring is preferably also performed, with the stirring speed preferably between 40 and 80 rpm, more preferably between 60 and 70 rpm; this stirring speed is suitable, neither too fast nor too slow, which increases heat exchange efficiency while avoiding excessive foaming.

[0045] To address the seasonal variations in milk production and the imbalance between raw milk production areas and consumption regions, this invention's freezing method, compared to the traditional method of spray-drying surplus fresh milk into milk powder, has a smaller impact on the flavor and quality of frozen fresh milk, avoiding undesirable flavors and textures. Furthermore, compared to traditional freezing methods, this invention reduces the formation of large ice crystals during freezing, resulting in more uniform ice crystal size and less impact on the physicochemical properties of milk. The finished product is less prone to stratification and sedimentation, and has a longer shelf life. Additionally, the pulping method used in this invention reduces uneven concentrations caused by varying freezing and thawing rates among different milk components. This freezing method achieves deep freezing (-80℃) at a lower cost, avoiding the high construction and maintenance costs of deep freezing (-80℃) facilities.

[0046] Based on the above advantages, this invention also provides the application of the freezing method or the reconstitution-thawing method described in the above technical solutions in the production of dairy products. Specifically, when preparing dairy products from the thawed reconstituted milk obtained by the reconstitution-thawing method, this invention preferably heats, stirs, and homogenizes the thawed reconstituted milk before preparing the dairy products. This invention preferably heats the thawed reconstituted milk to 45–60°C, more preferably 50–55°C; the stirring time is preferably 10–20 min, more preferably 15 min. The homogenization temperature is preferably 50–60°C, and the pressure is preferably 15–18 MPa. The heating, stirring, and homogenization operations of this invention can obtain uniform reconstituted milk.

[0047] The dairy products described in this invention preferably include, but are not limited to, liquid milk, yogurt, or dairy beverages; the production method of the dairy products is not particularly limited, and can be prepared according to the product type. Using the freezing and thawing methods described in this invention helps to increase the processing stability during the production of dairy products.

[0048] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] 1. A method for freezing raw milk, comprising the following steps:

[0051] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0052] (2) At 4-6℃, the raw milk is subjected to reverse osmosis to remove some of the water, so that the protein content reaches 4.0%, the fat content reaches 4.5%, and the lactose content is 5.3%; the milk is stirred at 60 rpm / min in the milk container and then put into use.

[0053] (3) The raw milk obtained in step (2) is pumped to the freezing chamber for freezing using a centrifugal pump. The temperature of the freezing medium in the freezing chamber jacket is set to -20℃. The distance between the stirring blade and the surface of the rotating drum is set to 0.2mm, the rotation speed is 80rpm / min, and the temperature is controlled between -18℃ and -20℃; the temperature of the resulting frozen milk slurry is set to -3℃. To reduce air contamination, the vacuum degree in the freezing chamber is set to 60kPa.

[0054] (4) Fill the frozen raw milk obtained in step (3) into packaging bags or iron drums and seal them, and then quickly freeze them with air cooling in a timely manner; set the quick-freezing temperature to -18℃ and store them for later use.

[0055] 2. A method for refreezing and thawing frozen raw milk, comprising the following steps:

[0056] (1) The frozen raw milk prepared in step 1 is demolded in a 4°C cold storage for 6 hours, and the demolded product is sent to a homogenizer to make ice slurry.

[0057] (2) The raw milk ice slurry prepared in step (1) is heated to 4-6°C through a heat exchanger via a pipe and stirred at 60 rpm / min to obtain reconstituted frozen raw milk.

[0058] (3) Heat the reconstituted frozen raw milk in step (2) to 50°C and homogenize it under 18MPa conditions.

[0059] The homogenized reconstituted fresh milk was pasteurized and then packaged to obtain the final product (dairy product); the pasteurization conditions were 75℃ for 15s.

[0060] Example 2

[0061] 1. A method for freezing raw milk, comprising the following steps:

[0062] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0063] (2) At 4-6℃, the raw milk is subjected to reverse osmosis to remove some of the water, so that the protein content reaches 4.0%, the fat content reaches 4.5%, and the lactose content reaches 5.3%; it is stirred at 60 rpm / min in the milk container and then put into use.

[0064] (3) The raw milk obtained in step (2) is pumped to the freezing chamber for freezing using a centrifugal pump. The temperature of the freezing medium in the freezing chamber jacket is set to -20℃. The distance between the stirring blade and the surface of the rotating drum is set to 0.2mm, the rotation speed is 80rpm / min, and the temperature is controlled between -18℃ and -20℃. The temperature of the resulting frozen milk slurry is set to -3℃. To reduce air contamination, the vacuum degree in the freezing chamber is set to 60kPa.

[0065] (4) Fill the frozen raw milk obtained in step (3) into packaging bags or iron drums and seal them, and then quickly freeze them with air. Set the quick-freezing temperature to -18℃ and store them for later use.

[0066] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0067] (1) The frozen raw milk prepared in step 1 was demolded in an 80°C hot air tunnel for 0.1 h. The demolded product was crushed and then homogenized into ice slurry.

[0068] (2) The raw milk ice slurry prepared in step (1) is heated to 4-6°C through a heat exchanger via a pipe and stirred at 60 rpm / min to obtain reconstituted frozen raw milk.

[0069] (3) Heat the reconstituted frozen raw milk from step (2) to 50°C, stir for 15 minutes, then homogenize and pre-pasteurize at 55°C and 18MPa, and cool for later use.

[0070] The product from step (3) that underwent pre-sterilization was homogenized and subjected to ultra-high temperature sterilization before being filled to obtain the final product. The ultra-high temperature sterilization conditions were 137°C for 6 seconds.

[0071] Example 3

[0072] 1. A method for freezing raw milk, comprising the following steps:

[0073] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0074] (2) At 4-6℃, the raw milk is subjected to reverse osmosis to remove some of the water, so that the protein content reaches 6.0%, the fat content reaches 8.0%, and the lactose content is 8.8%. Stir at 60 rpm / min in the milk container and set aside.

[0075] (3) The raw milk obtained in step (2) is pumped to the freezing chamber for freezing using a centrifugal pump. The temperature of the freezing medium in the freezing chamber jacket is set to -20℃. The distance between the stirring blade and the surface of the rotating drum is set to 3mm, the rotation speed is 80rpm / min, and the temperature is controlled between -18℃ and -20℃. The temperature of the resulting frozen milk slurry is set to -4℃. To reduce air contamination, the vacuum degree in the freezing chamber is set to 80kPa.

[0076] (4) Fill the frozen raw milk obtained in step (3) into packaging bags or iron drums and seal them, and then quickly freeze them with air. Set the quick-freezing temperature to -18℃ and store them for later use.

[0077] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0078] (1) The frozen raw milk prepared in step 1 was demolded in an 80°C hot air tunnel for 0.2 hours. The demolded product was crushed and then homogenized into ice slurry.

[0079] (2) The raw milk ice slurry prepared in step (1) is heated to 4-6°C through a heat exchanger via a pipe and stirred at 60 rpm / min to obtain reconstituted frozen raw milk.

[0080] (3) Heat the reconstituted frozen raw milk from step (2) to 50°C, stir for 15 minutes, then homogenize and pre-pasteurize at 60°C and 15 MPa, and cool for later use.

[0081] (4) The product that has undergone pre-sterilization in step (3) is homogenized and ultra-high temperature sterilized and then filled to obtain the final product. The ultra-high temperature sterilization conditions are 137°C for 6 seconds.

[0082] Example 4

[0083] 1. A method for freezing raw milk, comprising the following steps:

[0084] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0085] (2) At 4-6℃, the raw milk is subjected to reverse osmosis to remove some of the water, so that the protein content reaches 8.0%, the fat content reaches 9.2%, and the lactose content is 12%. Stir at 80 rpm / min in the milk container and set aside.

[0086] (3) The raw milk obtained in step (2) is pumped to the freezing chamber for freezing using a centrifugal pump. The temperature of the freezing medium in the freezing chamber jacket is set to -20℃. The distance between the stirring blade and the surface of the rotating drum is set to 0.3mm, the rotation speed is 80rpm / min, and the temperature is controlled between -18℃ and -20℃. The temperature of the resulting frozen milk slurry is set to -2.5℃. To reduce air contamination, the vacuum degree in the freezing chamber is set to 80kPa.

[0087] (4) Fill the frozen raw milk obtained in step (3) into packaging bags or iron drums and seal them, and then quickly freeze them with air. Set the quick-freezing temperature to -18℃ and store them for later use.

[0088] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0089] (1) The frozen raw milk prepared in step 1 was demolded in a hot air tunnel at 60°C for 0.2 hours. The demolded product was crushed and then homogenized into ice slurry.

[0090] (2) The raw milk ice slurry prepared in step (1) is heated to 4-6°C through a heat exchanger via a pipe and stirred at 60 rpm / min to obtain reconstituted frozen raw milk.

[0091] (3) Heat the reconstituted frozen raw milk prepared in step (2) to 50°C, stir for 15 min, then homogenize and pre-pasteurize at 50-60°C and 15-18 MPa, and cool for later use.

[0092] (4) The product pre-sterilized in step (3) is homogenized and sterilized, and then filled to obtain the final product. Sterilization is performed by steam immersion sterilization at 147°C for 4 seconds. After sterilization, it is preferable to perform aseptic homogenization again before filling at 60°C and 23 MPa.

[0093] Example 5

[0094] 1. A method for freezing raw milk, comprising the following steps:

[0095] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0096] (2) At 4-6℃, the raw milk is ultrafiltered to remove some of the water, so that the protein content reaches 10.0%, the fat content reaches 13.2%, and the lactose content is 6.0%. Stir at 60 rpm / min in the milk container and set aside.

[0097] (3) The raw milk obtained in step (2) is pumped to the freezing chamber for freezing using a centrifugal pump. The temperature of the freezing medium in the freezing chamber jacket is set to -20℃. The distance between the stirring blade and the surface of the rotating drum is set to 0.1mm, the rotation speed is 80rpm / min, and the temperature is controlled between -18℃ and -20℃. The temperature of the resulting frozen milk slurry is set to -2.5℃. To reduce air contamination, the vacuum degree in the freezing chamber is set to 80kPa.

[0098] (4) Fill the frozen raw milk obtained in step (3) into packaging bags or iron drums and seal them, and then quickly freeze them with air. Set the quick-freezing temperature to -18℃ and store them for later use.

[0099] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0100] (1) The frozen raw milk prepared in step 1 was demolded in a hot air tunnel at 60°C for 0.1 h. The demolded product was crushed and then homogenized into ice slurry by a homogenizer.

[0101] The subsequent steps are the same as in Example 3.

[0102] Comparative Example 1

[0103] A method for preparing raw milk, comprising the following steps:

[0104] (1) Select whole milk powder that meets national standards and add water in a certain proportion to reconstitute milk with a protein content of 3.1% and a fat content of 3.4%.

[0105] (2) Stir the reconstituted milk obtained in step (1) at a speed of 50 rpm / min and heat it to 55°C for homogenization. The homogenization pressure is 18 MPa.

[0106] (3) The reconstituted raw milk after homogenization in step (2) is sterilized at 137°C for 4 seconds.

[0107] (4) The sterilized milk is filled and refrigerated at 25°C.

[0108] Comparative Example 2

[0109] 1. A method for freezing raw milk, comprising the following steps:

[0110] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×105 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0111] (2) Raw milk is partially dehydrated by reverse osmosis, resulting in a protein content of 5.0%, a fat content of 7.8%, and a lactose content of 7.5%. The milk is stirred at 60 rpm / min in a milk container and then set aside.

[0112] (3) At 4-6℃, the raw milk from step (2) is filled into plastic bags or barrels, sealed, and then frozen in a -18℃ freezer for later use.

[0113] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0114] (1) Transfer the frozen raw milk prepared in step 1 into the thawing chamber to thaw; the temperature of the thawing chamber is 10℃ and the thawing time is 12h.

[0115] (2) The thawed raw milk obtained in step (1) is heated to 55°C, stirred for 15 min, homogenized at 18-20 MPa, and then pre-pasteurized. The pasteurization conditions are 85°C for 15 s, and then cooled for later use.

[0116] (3) The pre-pasteurized milk obtained in step (2) is subjected to ultra-high temperature sterilization at 137°C for 6 seconds. Homogenization is required before sterilization at 55°C and 20 MPa. Then, it is cooled to below 20°C and filled.

[0117] Comparative Example 3

[0118] 1. A method for freezing raw milk, comprising the following steps:

[0119] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0120] (2) Raw milk is ultrafiltered to remove some water, resulting in a protein content of 6.0%, a fat content of 8.0%, and a lactose content of 5.0%. It is stirred in a milk container at 60 rpm / min and then set aside.

[0121] (3) At 4-6℃, the raw milk from step (2) is filled into plastic bags or barrels, sealed, and then frozen in a -18℃ freezer for later use.

[0122] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0123] (1) Transfer the frozen raw milk prepared in step 1 into a thawing chamber to thaw. The temperature of the thawing chamber is 4℃, and the thawing time is 20h.

[0124] (2) The thawed raw milk obtained in step (1) is heated to 55°C, stirred for 15 min, homogenized at 18-20 MPa, and then pre-pasteurized. The pasteurization conditions are 85°C for 15 s, and then cooled for later use.

[0125] (3) The pre-pasteurized milk obtained in step (2) is subjected to ultra-high temperature sterilization at 137°C for 6 seconds. Homogenization is required before sterilization at 50°C and 20 MPa. Then, it is cooled to below 20°C and filled.

[0126] Comparative Example 4

[0127] 1. A method for freezing raw milk, comprising the following steps:

[0128] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0129] (2) The raw milk is partially dehydrated by reverse osmosis, resulting in a protein content of 6.0%, a fat content of 8.0%, and a lactose content of 8.8%. It is then stirred at 60 rpm / min in a milk container and set aside for use.

[0130] The remaining steps are the same as in Comparative Example 3.

[0131] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0132] The steps are the same as in Comparative Example 3.

[0133] Comparative Example 5

[0134] 1. A method for freezing raw milk, comprising the following steps:

[0135] (1) Select raw milk that meets national standards, with a total bacterial count of less than 1×10⁻⁶. 4 cfu / mL, somatic cell count less than 2×10 5 The milk should contain at least 3.1% protein and at least 3.4% fat per liter.

[0136] (2) At 4-6℃, the raw milk is subjected to reverse osmosis to remove some of the water, so that the protein content reaches 8.0%, the fat content reaches 9.2%, and the lactose content is 12%. Stir at 80 rpm / min in the milk container and set aside.

[0137] (3) At 4-6℃, the raw milk from step (2) is filled into plastic bags or barrels, sealed, and then frozen in a -18℃ freezer for later use.

[0138] 2. A method for reconstituted frozen raw milk, comprising the following steps:

[0139] (1) Transfer the frozen raw milk prepared in step 1 into a thawing chamber to thaw. The temperature of the thawing chamber is 4℃, and the thawing time is 36h.

[0140] (2) Heat the reconstituted frozen raw milk prepared in step (1) to 50°C, stir for 15 min, then homogenize and pre-pasteurize at 50-60°C and 15-18 MPa, and cool for later use.

[0141] (3) The product pre-sterilized in step (2) is homogenized and sterilized, and then filled to obtain the final product. Sterilization is performed by steam immersion sterilization at 147°C for 4 seconds. After sterilization, it is preferable to perform aseptic homogenization again before filling at 60°C and 23 MPa.

[0142] Test Example 1

[0143] 1) Determination of the thawing state and heat treatment stability of frozen raw milk:

[0144] To evaluate the condition of the samples after thawing, approximately 1 kg of frozen samples were thawed according to the corresponding thawing methods in the examples and comparative examples. After thawing, the liquid weight accounted for more than 95% of the total mass of the frozen sample after passing through a 6 mm neck funnel. The thawing speed evaluation table is shown in Table 1.

[0145] Table 1 Evaluation Table of Thawing Speed

[0146] thawing speed fast Faster generally Slower slow Thawing time, T 0<T≤1h 1<T≤4h 4<T≤8h 8<T≤20h T>20h

[0147] After storing approximately 1 kg of frozen samples for 30 days, the example samples were thawed according to the corresponding thawing method, placed in 1L plastic bottles, and allowed to stand for 30 minutes for observation. The comparative samples were directly thawed in 1L plastic bottles according to the corresponding method and observed directly. After observation inside the packaging, the samples were slowly poured along one side of a glass plate to observe for granular substances or lumps. The evaluation criteria for sample texture and state are shown in Table 2.

[0148] Table 2 Evaluation of Sample Texture and Condition

[0149]

[0150] The thawing state and heat treatment stability of the frozen raw milk in Examples 1-5 and Comparative Examples 1-5 were evaluated according to the above method, and the results are shown in Table 3.

[0151] Table 3. Evaluation results of frozen raw milk after thawing in Examples 1-5 and Comparative Examples 1-5.

[0152]

[0153]

[0154] 2) The shelf life and taste of the finished milk products prepared in Examples 1-5 and Comparative Examples 1-5 were evaluated:

[0155] The finished milk samples prepared in Examples 1-5 and Comparative Examples 1-5 were bottled into 100mL plastic bottles for shelf-life and taste evaluation. To reduce shelf-life tracking time, an accelerated shelf-life test at 37℃ in the dark was used. To better evaluate the sensory characteristics of the raw milk samples prepared in Examples 1-5 and Comparative Examples 1-5, 10 technicians were selected to conduct sensory evaluations according to the industry standards "RHB101 Sensory Quality Evaluation Guidelines for Pasteurized Milk" and "RHB102 Sensory Quality Evaluation Guidelines for Sterilized Milk". The evaluation guidelines are shown in Tables 4-5. The evaluation results were the average score of the 10 technicians, and the results are shown in Table 6.

[0156] Table 4 Sensory Evaluation Table for Pasteurized Milk

[0157]

[0158]

[0159] Table 5 Sensory Evaluation Table for Sterilized Milk

[0160]

[0161]

[0162] Table 6. Sensory evaluation results of raw milk in Examples 1-5 and Comparative Examples 1-5

[0163]

[0164] Through the above embodiments and comparative examples, it can be seen that the present invention not only solves the contradiction between milk source and output, thereby reducing the waste of raw milk and the problems of high production costs and poor flavor in processing milk powder, but also solves the problems of slow freezing and thawing speeds in traditional freezing methods, and especially the impact of ice crystals formed during the freezing process on the stability of milk after reconstitution, particularly for milk with high dry matter content.

[0165] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for freezing raw milk, characterized in that, Includes the following steps: Fresh milk is concentrated to obtain concentrated fresh milk; The concentrated raw milk is injected into a freezer chamber with a rotating drum for freezing. During the freezing process, a stirring scraper connected to the inner wall of the rotating drum is used to scrape off the formed frozen liquid layer to obtain frozen milk paste. The frozen milk slurry is filled into a storage container and quick-frozen to obtain frozen raw milk; The thickness of the liquid freezing layer is 0.1~3mm; the outlet temperature of the freezing chamber with the rotating drum is -8~-2℃; The distance between the edge of the stirring scraper and the inner wall of the rotating drum is 0.1~5mm, and the angle is 10~30°; the rotation speed of the stirring scraper is 30~150rpm; the temperature of the stirring scraper and the rotating drum are kept consistent.

2. The freezing method according to claim 1, characterized in that, The freezing and scraping are performed under vacuum conditions, wherein the vacuum degree is 0.01~0.08 MPa.

3. The freezing method according to claim 1, characterized in that, The concentration method includes vacuum falling membrane concentration, reverse osmosis concentration or ultrafiltration concentration; the concentrated raw milk has a protein content of 3.5% to 10%, a fat content of 3.8% to 13.5%, and a lactose content of 4.6% to 5.5%.

4. The freezing method according to claim 1, characterized in that, The temperature in the freezer compartment with the rotating drum is -25 to -10°C.

5. The freezing method according to claim 1, characterized in that, The quick-freezing method includes air-cooled quick-freezing, and the quick-freezing temperature is not lower than -18°C.

6. A method for refreezing and thawing frozen raw milk obtained by the freezing method according to any one of claims 1 to 5, characterized in that, Includes the following steps: The frozen raw milk is unmolded, and the unmolded frozen raw milk is subjected to ice slurry treatment to obtain raw milk ice slurry. The raw milk ice slurry is heated to 4-6°C to obtain thawed reconstituted milk.

7. The method for restoring and thawing according to claim 6, characterized in that, The demolding method includes low-temperature demolding, room-temperature demolding, or hot demolding. The temperature of low-temperature demolding is not higher than 10°C; the temperature of hot demolding is 60~80°C; and the demolding time is not higher than 5 hours.

8. The application of the freezing method according to any one of claims 1 to 5 or the reconstitution thawing method according to claim 6 or 7 in the production of dairy products.

9. The application according to claim 8, characterized in that, Before producing dairy products, the process further includes heating, stirring, and homogenizing the thawed reconstituted milk; the temperature of the heated reconstituted milk is 45~60℃.

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