Fermentation That Fails to Start Properly
A fermentation that fails to start properly is still considered a stuck fermentation, but the reasons for its failure to begin may be different from those of a fermentation that stalls towards the end. Most of the reasons can be attributed to the yeast and the factors that affect its health. So, let’s start with the basics and go from there.
It is important to note that just because the airlock is not bubbling, it does not necessarily mean that the beer is not fermenting. The only reliable way to check the progress of fermentation is by taking a hydrometer reading.
The Viability and Quality of the Yeast
This is the first factor to consider if the fermentation starts slowly and then gets stuck or fails to start at all. Every package of yeast you purchase will have either a production date or a use-by date. This information is crucial in determining whether you are pitching healthy and viable yeast cells or simply poor-quality and dead cells. If you have kept a package of yeast for a long time, it is possible that the viability of the cells has decreased too much, resulting in an insufficient number of healthy yeast cells to initiate fermentation properly.
If you are using old or ineffective yeast, pitching a new package should initiate fermentation as expected.
Temperature of the Wort
This is the next item on the checklist if you are experiencing a slow or non-starting fermentation, or if the fermentation becomes stuck. If the temperature inside the fermenter is too low, it can inhibit yeast activity. Different yeast strains work best within specific temperature ranges. If you leave the fermenter in a cold garage, it may be too cold for the yeast to become active.
The ideal temperature range for most ale yeasts is around 18°C – 21°C, while lager yeasts prefer lower temperatures, around 7°C – 14°C. If your beer is kept in a location that is too cold, the yeast will likely struggle to begin fermentation.
Similarly, higher temperatures can also pose problems. If you pitch the yeast when the wort is too hot, there is a possibility of killing the yeast. In this case, fermentation will not even have a chance to start.
If the fermenter is placed in a spot where temperature fluctuations are likely or if it goes outside the ideal temperature range for the yeast, move it to a more suitable location. If you suspect that you pitched the yeast into wort that was too hot, you will need to pitch new, healthy yeast.
Lack of Oxygen in the Wort
Yeast cells require oxygen to reproduce. This is why it is recommended to aerate the wort as it is transferred into the fermenter.
Most brewers rely on splashing or movement during pouring to aerate the wort, as it is the simplest way to introduce the necessary oxygen. Some brewers use aeration devices attached to a drill, for example, to inject air into the wort. Others even use pure oxygen through an aeration stone. For most brewers, pouring the wort from a height is sufficient to introduce enough oxygen. However, as the gravity of the beer increases, the additional stress placed on the yeast may result in a lack of oxygen, leading to a stuck fermentation due to insufficient resources for yeast reproduction.
If you neglect this simple step of introducing oxygen just before pitching the yeast, it can cause the yeast to stall, increase the lag time before fermentation starts, and result in a stuck fermentation. In this case, the best practice is to aerate the wort and pitch fresh, healthy yeast.