Heat treatment of milk -Pasteurization, Sterilization, Various Methods

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The main purpose of heat treatment of milk is to make it safe for human consumption and increase its shelf life. Thermal processing is an important part of milk and milk product manufacturing. It involves using heat to kill harmful bacteria in milk. The most resistant bacteria is Bacillus tuberculosis, so if a heat treatment can destroy this bacteria, it can destroy other pathogens in milk as well. The time and temperature combinations for heat treatments are optimized considering both microbiological effects and quality aspects.
Different Categories of Heat Treatments:

  1. Pasteurization: Pasteurization is a heat treatment process that aims to make milk safe for consumption by killing harmful bacteria while preserving its flavor and nutritional properties. There are two methods:

    a. Low Temperature Long Time (LTLT): In this method, milk is heated to 63°C and held at that temperature for 30 minutes. It is suitable for small-scale operations and requires lower initial equipment costs.

    b. High Temperature Short Time (HTST): HTST pasteurization involves heating milk to a minimum of 72°C for at least 15 seconds, followed by immediate cooling to 4°C. This method is more commonly used for large-scale milk processing due to its efficiency and continuous flow.
  2. Thermization: Thermization is a heat treatment process that involves heating milk below the temperature required for pasteurization. It is used when immediate pasteurization is not possible, and some milk needs to be stored for a short period before further processing. Milk is heated to 63-65°C for 15 seconds and rapidly chilled to 4°C or below to inhibit the growth of bacteria.
  3. Sterilization: Sterilization is a heat treatment process that involves subjecting milk or condensed milk to high temperatures for a longer duration to ensure complete sterilization. This process is typically used for milk that will be stored for extended periods without refrigeration. The temperature and time parameters for sterilization can vary but generally range from 115-120°C for 20-30 minutes.
  4. Ultrapasteurization: Ultra-pasteurization is a more intense form of pasteurization that extends the shelf life of milk by 15-30 days. Milk is heated to temperatures between 115-121°C for a very short period of 2-4 seconds. The milk is then rapidly cooled to below 4°C. This process requires stringent hygienic practices and involves packing the milk in pre-sterilized containers to maintain its extended shelf life.
  5. Ultra-High Temperature Treatment (UHT): UHT treatment is a technique used to preserve liquid food products, including milk, by exposing them to brief intense heating. Milk is heated to temperatures between 135-150°C for 1-6 seconds, which effectively kills bacteria and spores. UHT-treated milk can be stored at room temperature for an extended period without refrigeration, as long as the packaging remains sealed.

Categories Table of Heat Treatment of Milk

Treatment Temperature (°C) Time
Pasteurization – LTLT 63 30 minutes
Pasteurization – HTST (milk) 72 15-20 seconds
Pasteurization – HTST (cream) >80 15 seconds
Thermization 57-68 15 seconds
Ultra-Pasteurization 115-130 2-4 seconds
UHT 135-150 1-6 seconds
Sterilization 115-121 3-13 minutes

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