When it comes to pitching yeast, temperature is a crucial factor that can greatly impact fermentation. While different yeast strains have different temperature ranges, there is a general consensus among brewers that certain temperatures are too cold to pitch yeast effectively.
One common temperature that is considered too cold for most ale yeast is 60°F (15.5°C). This is because ale yeast strains typically prefer a slightly warmer environment to kickstart fermentation. At 60°F, the yeast metabolism slows down, and they become less active, leading to a delayed and sluggish fermentation process.
However, it's important to note that not all ale yeast strains are the same, and some may have slightly different temperature preferences. Some yeasts, like Belgian ale strains, may tolerate slightly lower temperatures without significant issues. Nevertheless, 60°F is generally considered too cold for most ale yeast strains.
On the other hand, a temperature of 65°F (18.3°C) is generally acceptable for pitching ale yeast. While it is still on the lower side of the optimal temperature range for most ale yeast strains, it is within the acceptable range and should not cause major problems. At 65°F, you can expect the fermentation process to proceed, although it may be slower compared to fermentations carried out at higher temperatures.
It's worth mentioning that while yeast can generate some heat during fermentation, relying solely on the yeast to bring the temperature up to the desired range is not recommended. It's best to ensure that the wort is at the desired temperature before pitching the yeast. This can be achieved by utilizing temperature control methods such as a fermentation chamber, a heat source, or a cooling system, depending on the situation.
In my personal brewing experience, I have encountered situations where I pitched yeast at temperatures that were too cold. One time, I brewed an IPA and mistakenly pitched the yeast at around 58°F (14.4°C). As a result, fermentation took much longer to start, and the yeast seemed to struggle to fully attenuate the beer. The final product had a slightly sweeter taste than intended, likely due to the slower fermentation process caused by the lower pitching temperature.
To summarize, 60°F (15.5°C) is generally considered too cold for most ale yeast strains, while 65°F (18.3°C) is acceptable but may result in slower fermentation. It's important to control and maintain the desired temperature throughout the fermentation process to ensure optimal yeast activity and the desired flavor profile in the final beer.