Fermentation activity is a measure not really used in brewing (yet). It is the quantitative measure of how fast the yeast in consuming sugars into its secondary products.
After developing the Airlock, which has a very presise measurement of fermentation activity, we were baffled by how mesmerizing it is. Take a look at the time-lapse below, and you'll understand it yourself.
The green graph displays exactly the dynamics of the fermentation, and the main stages of fermentation is clearly visible:
1. The Lag Phase
Typically 0 to 15 hours. In the example above, distillers yeast were used to create a vigorous fermentation. The lag phase is therefore only about 30 minutes long.
2. Exponential Growth Phase
Already seen in the very first second of the video. The fermentation activity rises non-linear, and the yeast starts consuming sugars and produce CO2.
3. Stationary Phase
Occurs roughly 3 seconds into the video. The curve is flattened, and the rate of fermentation stabilized. The majority of flavors and ethanol are produces in this phase, and by the
4. End of Fermentation
At 10 seconds a dramatic shift in fermentation activity is seen. The rate of decline varies hugely from beer to beer, and depends on sugar content, yeast strain, sugar composition, temperature and many other factors.
Although the fermentation activity has slowed to a minimum, processes are still active in the now so called "green beer" - a beer in which has not been stabilized in terms of flavors. The maturing phase reabsorbs diacetyl and aldehydes, and is argued one of the more important phases in brewing.