Brewing Process
Primary fermentation in homebrewing takes place in large glass or plastic carboys or food-grade plastic buckets, nearly always sealed. When sealed, the fermenter is stoppered with a fermentation lock which allows the carbon dioxide gas produced to vent, while preventing other gasses and particles from entering. During this time, temperatures should be kept at optimum temperature for the particular yeast strain being used. For ale this temperature is usually 18–24 °C (64–75 °F); for lager it is usually much colder, around 10 °C (50 °F); wine will start fermenting around 20 °C (68 °F); cider between 15–18 °C (59–64 °F). A vigorous fermentation then takes place, usually starting within twelve hours and continuing over the next few days. During this stage, the fermentable sugars (maltose, glucose, and sucrose) are consumed by the yeast, while ethanol and carbon dioxide are produced as byproducts by the yeast. A layer of sediment, the lees or "trub", appears at the bottom of the fermenter, composed of heavy fats, proteins and inactive yeast. Often, the brew is moved to a second fermenting vessel after primary fermentation called a secondary fermenter. This secondary fermentation process is often utilized by more advanced home brewers to enhance flavor. While not required, it is generally practiced by home brewers who wish to age or clarify their beer by removing it from the sediment left behind by primary fermentation.
Upon conclusion of fermentation, the beer is carbonated before it is consumed. This is typically done in one of two ways; force carbonation in a keg using compressed carbon dioxide, or bottle carbonation with priming sugar. Any bottle that is able to withstand the pressure of carbonation can be used, such as used beer bottles, flip-top bottles with rubber stoppers such as Grolsch, or even plastic bottles such as soda bottles, provided they are properly sanitized. Priming briefly reactivates the yeast that remains in the bottle, carbonating the brew. Homebrewed beers and lagers are typically unfiltered (filtering improves visual appearance of the product, but reduces its shelf life and complicates carbonation).
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