So you've prepared your wort in your fermenter, pitched the yeast, and you've anxiously waited hours or possibly even a day (or more) for some sort of indication that fermentation has started. It's not always easy to tell, but here are some signs to look for or things to check as indicators that your beer is fermentation has begun.
Air Lock Activity
Probably the most obvious one, bubbles in your air lock are a tell-tale sign that your beer is actively fermenting. As the yeast ferment your wort and consume the sugars contained within it, they produce carbon dioxide gas (amongst other things) as a byproduct of fermentation. The escaping of this gas through the air lock creates a bubbling effect as it passes through the liquid contained in the air lock. If you're seeing bubbles, then carbon dioxide gas is being created so fermentation is definitely underway.
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| An example of an air lock |
However, it's worth pointing out that if you don't see air lock activity, this doesn't necessarily mean fermenation isn't under way. If there is any kind of leak in the seal of the fermenter lid, then the gas will escape through there rather than the air lock, so check for other signs of fermentation before declaring your fermentation isn't underway.
Pressure Build Up in Fermenter Headspace
Similar to what was mentioned above with air lock activity, if you are using a pressure fermenter then any increase in pressure of the head space is a sure sign that things are underway, since the gas will build up and create pressure within the fermenter rather than escaping straight out of the air lock.
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| Any positive pressure on the spunding valve gauge is a sure sign that fermentation has started |
As soon as the pressure gauge on your spunding valve starts to move from 0, then it's a sign that fermentation is underway.
Visual Signs - Bubbles and Krausen
Within several hours of pitching your yeast, you may start to see small bubbles forming on the surface of your wort. This is generally an indication of yeast activity and a good sign that fermentation is slowly beginning and ramping up.
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| An example of Krausen in a fermenter |
As fermentation progresses, a krausen will develop on the top of the fermenting wort which is a sure sign that things are well and truly underway and progressing as expected. Krausen can come in many different colours and textures, but it's generally a foamy like substance, kind of like "mousse" with any colour or colours ranging from white to brown.
Unfortunately if you don't have a clear or translucent fermenter then visual signs may not be achievable (unless you open the lid of your fermenter and look inside), in which cause other methods of checking may be preferable.
Reduction in Gravity
The most reliable way to know that fermentation is underway is a change (reduction) in the gravity reading of your wort. Gravity refers to the amount of sugar in the wort, and as the yeast begin to consume the sugar in the wort, the gravity will begin to decrease.
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| Gravity readings using a floating hydrometer remove any doubt as to whether or not fermenation has begun |
Along with being able to determine the alcohol contained in your beer, this is another reason to measure the starting gravity of your wort prior to pitching the yeast. If the gravity has reduced from your starting gravity then this is a guarantee that fermentation has begun.
Gravity is measured using a hydrometer - floating hydrometers are the most common and popular, but require a sample to be drawn from the fermenter in order to take a reading. There are also Wi-Fi capable hydrometers (like the RAPT Pill) that remain floating in your wort during fermentation that report real-time gravity readings which give a great insight into the state and progress of fermentation.
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