Determine If Your Beer Is Done Fermenting

Updated: Apr 14

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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. We do this at our brewing project Danger Shed with every single batch. The simple data that we gather can be referenced for future batches and to find patterns in fermentation.


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IDENTIFYING END OF FERMENTATION IS HARD


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.


fermenting beer
Without analyzing the change in gravity it is difficult to accurately identify the end of fermentation

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METHODS TO DETERMINE FINISHED FERMENTATION


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.


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OUR METHOD FOR DETERMINING FINISHED FERMENTATION


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.


Fermentation data table
Record your data into a table

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.


Beer fermentation charts
Make simple graphics so you can visualize the data


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.



beer fermentation chart
When the gravity curve levels out for a day or more, primary fermentation is complete


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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