Ever since Louis Pasteur discovered that harmful organisms could be killed off by applying heat to wine, pasteurization has been one of the most important operations in manufacturing food, dairy, beer, juice, and all beverages. There are a number of different methods of pasteurization and it's important to understand these. I will seek to explain as clearly as possible these methods in the following few paragraphs.
Continuous VS. Batch (VAT):
Simply put, batch pasteurization involves heating a large amount (or batch) of the liquid all at once to about 145 degrees Fahrenheit for 30 minutes. It's kind of like heating water in a pot on your stove, but on a much larger scale. The temperature and hold time varies depending on the liquid's acidity. Specific guidelines are prescribed by the FDA for each industry. One very important form of pasteurization that could fall into this category is tunnel pasteurization. Tunnel pasteurization involves filling and capping the liquid into glass bottles or aluminum cans prior to pasteurization. The liquid, bottle, and cap are then heated to around 160 degrees Fahrenheit for 20 minutes or so. This process is often used by beer, tea, and energy drink companies whose flavor system can vary greatly with the amount of time their product cooks, or in the case of cans; it's the easiest way to avoid any contamination. Other than those reasons, batch pasteurization has largely been replaced by Continuous pasteurization.
Continuous pasteurization has numerous advantages over VAT pasteurization including less time, fewer sanitation variables, and energy savings. The name "continuous" is given to this process because only a part of the batch (anywhere from 5-100 gallons per minute) is pasteurized continually as it flows through a heat exchange. Continuous pasteurization is achieved using either a plate heat exchanger or tubular heat exchanger. Plate is used often with the pasteurization of milk and non pulpy liquids. If the liquid is thick, pulpy, or fibrous, as many juices are, a tubular heat exchange is used to avoid blockage in the system and burning. The heating medium is either water or steam.
Defining HTST, UP, UHT, Flash Pasteurization, and Hot Fill
Within continuous pasteurization there are a number of different processes. You've probably heard of HTST (high temperature short time,) Ultra pasteurization, and Ultra-high temperature sterilization. Each of these forms of pasteurization has a different temperature and hold time. For HTST pasteurization, the temperature is typically 165 degrees to 180 degrees Fahrenheit. The hold time is anywhere from 3 to 15 seconds. Ultra pasteurization ranges from 190 degrees and 212 degrees Fahrenheit with hold times of 1 to.01 seconds. UHT sterilization is 280 degrees for 2 seconds. The shelf life and flavor of the liquid can be affected depending on which process is used.
With either of these processes a "Flash Pasteurization" can be achieved if the liquid is immediately passed through a second heat exchange prior to bottling, cooled to ambient temperature, and filled cold in an aseptic environment. This is often the case with UP and UHT pasteurization.
A hot fill process is also used; usually with HTST pasteurization, where the liquid is filled into bottles while still hot, thus sterilizing the bottle and cap. The already bottled liquid can then pass through a cooling tunnel and return to ambient temperature as quickly or as slowly as you like. Advantages of the HTST pasteurization hot fill over the aseptic cold fill are lower cost, and 100% sterile product. It costs a lot of money to maintain an aseptic environment for cold filling, and on occasion, the bottle is not sterile when filled. One may see the aseptic process as the best because the liquid is hot for a shorter amount of time. Ultimately, you have to weigh the benefits and costs in order to decide which process is best for you. Often, you can counter the negative effects of a hot fill by the addition of antioxidants to the formula. From my experience, HTST pasteurization hot fill is the best option for perishable beverages such as fruit and vegetable juices, and teas.
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