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Bottling Beer
Flash Pasteurization
Pasteurization is an alternative to sterile filtration for reducing the number of harmful microorganisms in beer. The basis for pasteurization is the heating of the beer for a predetermined period of time at specific temperatures, thereby assuring the microbiological stability of the beer. A Pasteurization Unit (PU) is defined as a one-minute exposure to a temperature of 60ºC. A PU is a measure of the lethal effect on microorganisms of the heat treatment. The aim is to attain the minimum degree of pasteurization necessary to inactivate beer-spoiling organisms. Pasteurization is less common among craft brewers who are more apt to rely on sterile filtration. The two main types of pasteurization techniques are flash and tunnel. Flash pasteurization is used for continuous treatment of bulk beer prior to filling the bottles, cans, or kegs. It is typically carried out in a plate heat-exchanger before transferring the beer to the bright-beer tank. Tunnel pasteurization is used mainly for in-pack treatment following the crowning of the bottles.
Flash pasteurization is not widely used by breweries in North America (though it is very popular with the dairy and juice industries), but it has been widely adopted in Europe and Asia. There are many such systems in existence, most used for kegs, and some for bottles and cans. In flash pasteurization, the beer is heated to at least 71.5 to 74ºC and held at this temperature between 15 and 30 seconds. Flash pasteurization of beer typically uses a two- or three-stage plate heat exchanger with hot water as the heat exchange medium. The heat exchanger is designed so that a particular flow rate will achieve maximum efficiency. Consequently, the flow rate – not the temperature – must be adjusted to alter the number of PUs for a given beer.
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