Pasteurization is the process in which all disease producing bacteria is destroyed from a food or a liquid, as well as 90-99 percent of all other bacteria that may affect product quality. Pasteurization works to kill bacteria with high heat, helping reduce the transmission of diseases such as typhoid fever, tuberculosis, scarlet fever, polio and dysentery. Because of this, pasteurization is the most important function of a milk plant.
Methods of Pasteurization
There are many different levels and methods of pasteurization, which vary based off the temperatures used to heat up a product and the amount of time spent doing so. Deciding on what pasteurization method to use largely depends on the type of product you’re working with. When it comes to pasteurizing dairy products such as milk and cream, two of the most common types are vat pasteurization and HTST pasteurization.
Vat Pasteurization
Vat Pasteurization, also known as batch pasteurization or the holding method, is one of the original methods of pasteurization. In addition to milk processing, this method is commonly used in the dairy industry during the processing of yogurt, cheese, ice cream mixes, and more. Vat pasteurization destroys bacteria by heating every particle of milk or cream in properly designed and operated equipment for a half hour (which is considerably longer than most types of pasteurization).
Recommended Temperature For Vat Pasteurization
For vat pasteurization, it is necessary to heat the milk product to 145°F (63°C) for 30 minutes*. If the fat content of the milk product is 10 percent or greater, or a total solids of 18% or greater, or if it contains added sweeteners, the specified temperature shall be increased by 5°F (3°C). The presence of both butter granules and cream plug are possible in milk and cream. Agitation is necessary to achieve the proper consistency and texture as well as rapid, even heating. Incorrect agitation will cause churning.
Heating & Agitation Method For Vat Pasteurization
Finding the right balance of heating and agitation is important to efficiently operate a vat pasteurizer. If the heating temperatures are too low, the milk product temperature will not raise quickly enough. If heating temperatures are too high, the milk product may “cook on” the heating surface. The speed of heating is affected by the ability of your agitator to keep the product moving to, and away from, the heating surface. However, simply speeding up your agitator will not necessarily give you the desired result. Agitators are designed for certain speeds and highly efficient agitators may require high heating water temperatures. Failure to balance the heating surface with your agitation type and speed can result in improper pasteurization.
Holding Period For Vat Pasteurization
Vat pasteurization has to be done at a high temperature for a long period of time. During the holding period, the vat must remain closed to prevent cooling from occurring during pasteurization. Vats should have an airspace heater to keep the air above the product at or above 145°F. Airspace heaters also ensure the pasteurization of milk droplets that are splashed on the sides of the vat and condensate on the inside of the vat cover. The bottom and sides of the vat must be insulated or jacketed to maintain proper temperatures during the holding period.
HTST Pasteurization stands for High Temperature Short Time pasteurization and is also known as flash pasteurization or the continuous method. It has become one of the most common methods of pasteurization today. HTST pasteurization is a continuous process that efficiently and effectively destroys microorganisms in milk products.
Recommended Temperature For HTST Pasteurization
For HTST pasteurization, the milk product needs to be quickly raised to a temperature of at least 161° F (72° C) for a minimum of 15 seconds*, followed by rapid cooling. If the fat content of the milk product is 10% or greater, or a total solids of 18% or greater, or if it contains added sweeteners, the specified temperature shall be increased by 5°F (3°C).
Components of an HTST Pasteurization System
An HTST pasteurization system is a modular unit that includes a plate-and-frame heat exchanger, stainless steel balance tank, pumps, holding tube, valves, and controls. The heat exchanger sends the product through a series of stainless steel plates. The product flows on one side while the heating media flows on the opposite side to raise the temperature of the milk. If the required temperature or time requirements are not met then a flow diversion valve re-routes the product back through the heat exchanger.
Benefits of HTST Pasteurization
Vat pasteurization is the oldest method for pasteurizing food products, but High Temperature Short Time has gained favor with many in the food industry over the years. Some of the advantages of HTST include:
Large equipment capacity which allows for larger volumes at one time
Continuous process allows for bottling to begin when pasteurization begins
Highly energy efficient
Minimal chance of damage to milk product
Fully utilized regeneration
Equipment is easy to clean and sterilize
Thermophiles are less troublesome
Choosing a Pasteurization Method
When trying to decide which method of pasteurization will best suit your application, there’s a lot of things to think about. The most important factors you need to consider are your budget, the volume of product you are pasteurizing, and the heating pace you desire. Small-scale dairy operations tend to go with vat pasteurization. When it comes to financials, the holding method is the lower cost option. If you’re working with smaller batches, the lower temperatures and longer times can be more ideal. Processing plants that handle less than 1000 gallons daily may also use the pasteurizing vat as the storage tank. Standardization and the adding of vitamin concentrates can be done in the vat pasteurizer before heating. If a processing plant handles volumes in excess, then HTST would be the most economical and successful option. HTST systems are designed to work with increased quantities at higher efficiencies. But since the continuous method requires more components, it can be more expensive than the holding method. The pasteurization temperature and time chart below maps out the temperature and time required for each vat pasteurization and HTST pasteurization:
Additional Types of Pasteurization
There are several other pasteurization methods to learn about, each with their own set of benefits and disadvantages that can impact your operation in different ways. One common method is Higher Heat Shorter Time (HHST), which is a similar process to HTST but uses higher temperatures for a shorter duration and requires slightly different equipment. Another type is Ultra High Temperature (UHT), which is also referred to as aseptic processing. With UHT pasteurization, dairy products are heated for just a couple seconds at temperatures even higher than those used for HHST pasteurization before being quickly cooled down. There’s also a variety of non-thermal pasteurization methods which can allow for greater sustainability and efficiency when converting raw food items into finished products. These include High Pressure Processing (HPP), Pulsed Electric Field (PEF), and Microwave Volumetric Heating (MVH).
Find The Dairy Equipment and Solutions You Need at Zwirner Equipment
If you’re still unsure of which pasteurization method is best for your processing needs, or you’re in need of milk pasteurization equipment – you’ve come to the right place! The experts at Zwirner Equipment specialize in providing reconditioned stainless steel processing equipment to companies and plants all across the country. If you’re interested in learning more about our available inventory or the industrial services we offer, please fill out the form below or give us a call today! Call Today*Standards from the Grade “A” Pasteurized Milk Ordinance 2013, provided by the U.S. Department of Health and Human Services, Public Health Service and Food and Drug Administration.
