When we were in high school, we have all seen a strange looking tube which had a opened bulb on one side and an upright closed tube on the other. To perform an experiment with it, the first thing to do was to fill the tube with room temperature water, then a little sugar and about a tea spoon of yeast. The open end was then closed using some cotton. After a while, when one smelled the solution inside the tube, it felt like there was alcohol in it. However, there is also a change in the level of liquid in the upright side of the tube.
Was it magic?
Not at all! The yeast had fermented the sugar and produced good alcohol, and carbon dioxide as a byproduct. This experiment was first demonstrated by Wilhelm Kühne to show fermentation in yeast. The image above, is that of a Kühne’s fermentation tube (rendered using Rhino).
Yeast has a very useful enzyme called zymase. The yeast eats the sugar and expels the good alcohol, ethanol (not the bad kind, methanol, which is poisonous). Ethanol is the one present in any alcoholic beverage, and naturally, in beer.
A similar process happens as mentioned above while making beer. Beer is made from grains which have high carbohydrate content such as wheat, oats, barley etc. When (more or less coarsely) powdered grains are mixed with water and brought to a higher temperature. polysaccharide sugars are broken down into simple sugars, such as glucose. The liquid is strained. It can also be sparged to extract the remaining sugars in the strained grains. When this liquid is rapidly cooled, strained and yeast is added to it, the fermentation process can begin.
Of course, the amount of grains, water, yeast, and other additives like hops are appropriately measured before doing the process. The final mixture is transferred carefully into sterile vats. It is very important to make sure that there are no contaminants (such as bacteria), so that the final brew is not infected.
At this point, both alcohol and carbon dioxide production would have begun. Unless a particular temperature is maintained (it is different for different styles of beer), the yeast will die and the end product will be sweet, yet rather unpalatable liquid.
The large jars below are called carboys, or damajuana, here in Peru. Each of them is topped with a cork with a bunghole (No! It is not a slang in this context). There is a one way exhaust tube through the bunghole. The carbon dioxide escapes through this exhaust. There is also a sterile solution inside the exhaust made using a right ratio of water and a good acid-based no-rinse sterilizer .
The brown liquid on the top becomes the beer, ultimately. The mucky remnants on the bottom will settle down and allow room for further fermentation (the carboy to the left will not settle a lot; this image is of the last two carboys from a bigger batch… because the world does not run according to my convenience ).
It is very important that carboys are not filled to the brim, and they have a proper exhaust for the carbon dioxide to escape. Otherwise they will definitely burst, and all the efforts will be in vain. As the carbon dioxide escapes, the liquid inside the exhaust will also change its level. After this, there is a period of waiting (usually for a couple of weeks), and then the beer is bottled, and then, there it is again… another period of waiting for carbonation before selling or more appropriately drinking the beer.
The most important thing to have while brewing beer, is patience.