Updated: Jun 9
How do you know when your beer is done fermenting? We're going to show you how to figure this out by using simple analytics to help you visualize fermentation.
No Easy Task
Identifying the end of fermentation is one of the more difficult skills you develop as a brewer. Many schools of thought revolve around this question, and seasoned brewers are likely to have their own steadfast opinion of the "right" way to determine if the beer is done with primary fermentation. But here, we prefer to take a scientific approach and make decisions backed by data. But first, let's take a look at a few other methods for figuring this out.
Other Methods for Determining End of Fermentation
There are numerous ways you can go about this. Some are better than others, and some are more suited to the level of effort you are willing to put into properly monitoring your fermentation.
Wait 2 weeks - This is the most simple approach to take. Ferment your beer in the primary fermenter for 2 weeks...that's it. Essentially, this method removes the decision making process. However, it is generally preferable to take the beer off of the yeast when primary is done, reducing the risk of the yeast at the bottom of the fermenter from creating off flavors.
Watch the airlock - Yeast create carbon dioxide that escapes through the fermenter airlock during fermentation. When the yeast are working at full steam the airlock will be bubbling once a second or more and slow down over time as the yeast gradually run out of sugar to metabolize. So by looking at the airlock activity, you can make a good guess if fermentation is complete. The problem with this is that specific gravity readings may still be falling but at a rate slow enough for little or no airlock activity.
Subsiding Krausen - Krausen is the layer of yeast that forms on the top of the beer during primary fermentation. The krausen will be highest during the peak of primary fermentation and subside as primary winds down. Eventually, all or most of the krausen will fall back into the beer. This has similar faults to watching the airlock - you aren't really sure if fermentation is complete, or just close.
As the beer ferments, yeast converts sugar into alcohol and carbon dioxide. Over time, this process decreases the specific gravity. Eventually, the readings will level out, marking the end of primary fermentation.
1) Take a reading every day
During fermentation, you should be taking a temperature and gravity reading each day.
2) Create Graphics
Use this data to create a simple gravity curve with the day of fermentation on the X-axis, and the specific gravity on the Y-axis.
3) Look At the Rate of Change
Visualizing the fermentation curve provides an accurate and instant status on your beer’s progress. To determine if fermentation is complete, simply look for when there is little to no change in gravity from one day to the next.
4) Confirm Final Gravity
If there is little to no change in the curve for a day or more, your beer is likely done fermenting, and the last reading is the final gravity.
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