A review on Beer Pasteurization - The process and its effect on the quality of beer

Beer Pasteurization - When and how it started?  

Pasteurization process was discovered after the great French scientist Louis Pasteur was able to extend the quality of beer by holding the beer at 55 - 60^oC (131 - 140^oF) for a short time. Pasteurization and sterilization are confusing terms. In pasteurization, the beer is subject to sufficient heat to make the beer free from microbial spoilage. However, low levels of some microorganisms might still survive the heating, without causing spoilage of the beer. In sterilization, high temperature is applied to destroy microorganisms. The targeted microorganism of pasteurization is Saccharomyces cerevisiae.

Beer is pasteurized by two methods-

Tunnel Pasteurization

This pasteurization is applied to bottles and cans of beer. In tunnel pasteurization, there is a tunnel of stainless steel. The liquid-filled bottles and cans are passed through the tunnel where hot water at temperature 60 - 65^oC is sprayed on the finished product. After the hot bath, the bottles and cans are sprayed with cold water to cool them down to 20 - 25^oC. This pasteurization process is an ideal way to pasteurize beer. Tunnel pasteurization is very useful for commercial craft brewers for its advantages, such as - 

• Tunnel pasteurization offers an effective process in inhibiting pathogens and microorganisms.
• Tunnel pasteurization is applied to bottles and cans of beer. So there are fewer contamination microbes to beer. 
• It is easy to operate and reliable. 

The following video shows how beer cans are pasteurized by tunnel pasteurization

Flash Pasteurization

This pasteurization process is applied to large containers of beer such as kegs (a small barrel, especially one of less than 10 gallons in the US or 30 gallons). The beer undergoes a process called thermal bypass system. It is a type of heat exchanger where the beer flows one way in one pipe and heated water or steam flows the other way in the other pipe. When they pass each other, the temperature of the beer goes up and the water temperature goes down. It takes 20-30 seconds to complete the process at a temperature of 70 - 75^oC. The pasteurized beer then rapidly cooled to 20 - 25^oC before being filled into sterile containers. Flash pasteurization is only applied to the product, not to bottles or cans. 

Two types of flash pasteurization are applied to beer - 

Steady-state: The temperature, pressure, and flow remain constant during the process. Hot water of constant temperature is circulated in the system at a constantly controlled rate. 

Variable-state: The temperature, pressure, and flow are varied throughout the system. 

A problem with flash pasteurization is that the beer can be contaminated by microbes during packaging. But the tunnel pasteurization avoids this problem as the beers are already packaged before the pasteurization process.

The following video shows how the beer is pasteurized by flash pasteurization  

How pasteurization affects the quality of beer?

Yes, pasteurization of beer can affect the quality of the beer, though pasteurization is very important to prevent the microbial spoilage. During beer aging, fresh flavor decreases, while aged flavor compounds are formed. Especially trans-2-nonenal that is considered to be responsible for the development of cardboard-like flavors formed through oxidative reactions, has received much attention but some other aged flavors such as winey and solvent-like flavors are also formed. In recent years some brewers attempt a process called sterile filtration to exclude beer spoilage.


Source:
https://beerandbrewing.com/

Video source: 
https://www.khs.com/