In the previous article, the first two stages of the five-stage beer brewing process was discussed. In short, it involved germinating and crushing barley to a malt which turns starches into water soluble sugars. The malt is then mashed to a sweet liquid, called wort. These first two stages are important in determining the type of beer that is being made. The density of the wort is measured before the fermentation process begins.
Stage 3 : Fermentation
The wort is separated from the hops and sent through a liquid-cooling heat exchanger to be cooled to a temperature that is hospitable to yeast. Once the wort is cool enough, the yeast is added and fermentation begins. The yeast uses the sugars from the wort to grow and multiply, while it produces ethanol and carbon dioxide. Hence, these biochemical reactions of fermentation supplies the carbonation and the alcohol content of a beer.
Two types of fermentation exist – top fermentation and bottom fermentation. Bottom fermentation is used to make Lagers and it typically takes about two weeks. It is done at lower temperatures and the yeast sinks to the bottom of the vessel. Top fermentation is used to make sweeter, stronger beers called Ales and it takes about one week. Fermentation mostly takes place at the top of the vessel and at higher temperatures.
Many different types of yeast have been developed over the years and it is the chemical engineer’s responsibility to choose the right one for the specific fermentation process. It is important that the beer does not come into contact during the brewing process. Once the fermentation process is complete, the yeast is collected from the beer and it may be reused. Some breweries can use the same yeast for many years.
The density of the beer is measured during the fermentation process and compared to the original wort density to determine the beer’s alcohol content. The alcohol content will determine when the fermentation process should be stopped. If the process is stopped too early, the beer might might be very sweet with a low alcohol content and vice versa.
In the next article, we will discuss the final stages of the beer brewing process.