Prior to pitching yeast, should it be warmer or cooler than the wort?

The ideal scenario for pitching yeast is to have it cooler than the wort. This practice helps ensure a healthy fermentation process. Yeast is adapted to respond to certain temperature ranges, with different strains having specific requirements. When yeast is pitched at a cooler temperature than the wort, it minimizes the risk of thermal shock, which can result in off-flavors or sluggish fermentation due to the yeast possibly being stressed.

Moreover, the wort is generally at a higher temperature due to the brewing process, which can be detrimental if yeast is introduced at such elevated temperatures. A cooler temperature allows the yeast to acclimatize and establish itself as fermentation begins, which contributes to a more controlled and efficient fermentation environment.

This approach can also help prevent the production of undesirable byproducts that can occur in higher temperature conditions, such as fusel alcohols, which impact the flavor and aroma of the final beer. Therefore, having the yeast cooler than the wort is a critical factor for successful fermentation and the overall quality of the beer.