Homebrewing: Letting Your Beer Ferment

By Marty Nachel, Steve Ettlinger

Raw, sweet wort must undergo fermentation before it officially becomes beer, and bottling can’t take place until fermentation is complete. Fermentation of a 5-gallon batch usually takes a minimum of seven days, depending on the yeast, and fermentation activity can start anywhere in the first 12 to 24 hours after you add the yeast to the wort.

Fermentation starts slowly, gradually builds in intensity, and usually reaches a crescendo on the second or third day. When fermentation reaches its peak, the airlock may sound like an engine piston at low rev, with carbon dioxide bubbles making their hasty exit from the fermenter. A quick whiff of the escaping gas gives you your first aromatic experience of beer making.

Leave the fermenter alone for the duration of fermentation. The exact length of fermentation depends on the health and viability of the yeast and on the temperature at which fermentation takes place. Even as the activity slows and the bubbles in the airlock start emerging slowly, one at a time, fermentation may continue for several more days. Be patient. Don’t remove the airlock or fermenter lid to sneak a peek inside; you risk contaminating the beer. The general rule is to wait seven days minimum.

On the seventh day of fermentation, start paying close attention to the brew (no, it’s not the day to rest). With the aid of a wristwatch or a clock that has a second hand, count the amount of time between bubbles emerging from the airlock. When a minute or more elapses between bubbles, plan to bottle the next day or very soon thereafter. If after seven days the float piece in the airlock isn’t even floating, you should start bottling.

If you have a hydrometer, fill the hydrometer cylinder with a sample of beer through the spigot of the fermenter and take a hydrometer reading to verify that fermentation is complete.

After you take your hydrometer reading, don’t pour the sample from the cylinder back in with the rest of the beer; doing so risks contaminating it. More important, don’t throw the sample down the sink; it may be uncarbonated, but it’s still good beer, so drink it. You may be surprised by how good it already tastes. Ah!