Beer Fermentation Timeline

Once the wort has cooled to the correct temperature, generally between 18 and 22 ºC (65 to 71 degrees Fahrenheit), it can be transferred to the fermentation vessel. The wort then needs to be aerated to introduce oxygen. This typically takes about ten minutes.

Once the yeast has been added to the wort, fermentation takes place in four stages. Exactly how long each step takes will vary depending on the type of yeast used, whether you made a yeast starter and the temperature at which fermentation occurs.

• Lag Phase

• Exponential Fermentation Phase (High Krausen)

• Static Fermentation Phase

• Conditioning

Lag Phase

The lag phase is the time between when the yeast is added to the wort (pitched) and when active fermentation starts to take place. There will be no bubbles in the airlock during this period, and it might look like nothing is happening. But in fact, the yeast is busy absorbing oxygen and nutrients from the wort and is starting to grow and multiply in numbers.

The lag phase typically lasts from eight to twenty-four hours and can be reduced by using liquid yeast and preparing a yeast starter.

Exponential Fermentation Phase

Once the lag phase is over, the yeast starts consuming sugar from the wort, creating alcohol and carbon dioxide. At this point, the yeast multiplies rapidly; a thick layer of foam known as Krausen forms on top of the wort, and the airlock bubbles vigorously.

The exponential fermentation phase typically lasts between one and four days. During this period, the specific gravity drops rapidly as the sugar in the wort is consumed by the yeast.

Static Fermentation Phase

Once the exponential phase is over, the rate of yeast growth slows down. At this stage, the specific gravity drops more slowly, the layer of krausen on top of the wort drops down, and only the occasional bubble is seen in the airlock. Sometimes the airlock may stop bubbling entirely at this stage.

During the static fermentation phase, the yeast stops creating alcohol and starts cleaning up after itself, reabsorbing the unwanted byproducts produced during the exponential fermentation phase. The yeast begins to flocculate, clump together and sink to the bottom of the fermentation vessel.

This phase typically takes between three and ten days, during which time, after the airlock stops bubbling, you should take gravity readings to determine when fermentation has finished.

Conditioning Phase

Once fermentation has finished, the yeast and other sediment continue to sink to the bottom of the fermentation vessel. At this stage, you should be taking a gravity reading every two days until you get two successive readings that are the same. Indicating that fermentation is complete.