As an experienced sommelier and brewer, I can provide you with a detailed answer to the question of whether you should stir yeast when pitching.
When it comes to yeast pitching, it is generally best not to stir your wort after you have added the yeast. This is because stirring the wort can introduce unnecessary risks and potentially harm the yeast.
One of the main reasons for not stirring yeast after pitching is the risk of infection in your beer. By stirring the wort, you can kick up any airborne contaminants or bacteria that may be present, which can then find their way into your fermenter. This can lead to off-flavors and spoilage in your beer.
Additionally, stirring the wort after pitching can disturb the yeast that has settled on the sides of the fermenter. This yeast is crucial for fermentation as it plays a vital role in converting sugars into alcohol and carbon dioxide. By disturbing this yeast, you may hinder fermentation and potentially end up with a sluggish or stuck fermentation.
Furthermore, yeast is a delicate organism, and excessive agitation can cause stress to the yeast cells. Stirring can introduce excess oxygen into the wort, which can be detrimental to the yeast. While yeast requires oxygen during its initial growth phase, excessive oxygen can lead to oxidative stress and negatively impact yeast health and performance.
To ensure proper yeast pitching, it is recommended to thoroughly aerate your wort before adding the yeast. This can be done by vigorously shaking or splashing the wort, or by using an aeration stone or oxygenation system. This initial aeration will provide the yeast with the necessary oxygen for their growth phase without the risks associated with stirring after pitching.
In my personal brewing experience, I have found that following this approach of aerating the wort before pitching and avoiding stirring afterward has yielded better fermentation results. My beers have had cleaner flavors and a more efficient fermentation process.
To summarize, it is best to avoid stirring your wort after pitching yeast. Stirring can introduce infection risks, disturb settled yeast, and stress the yeast cells. Thoroughly aerating the wort before pitching is a better practice to ensure a healthy fermentation process.