As an experienced brewer and sommelier, I can tell you that Wyeast 34/70 is a lager yeast strain that is known for its clean fermentation profile and minimal production of diacetyl. Diacetyl is a compound that can give a buttery or butterscotch-like flavor to beer, and it is generally considered a flaw in most beer styles.
However, every yeast strain has the potential to produce some amount of diacetyl, and the levels can vary depending on fermentation conditions and yeast health. In the case of Wyeast 34/70, it is generally known for its low diacetyl production, making it a popular choice for lagers.
That being said, it is still a good practice to give your beer a diacetyl rest, especially if you are aiming for a flawlessly clean and crisp lager. The diacetyl rest is a technique used to ensure that any diacetyl produced during fermentation is cleaned up by the yeast before lagering.
To perform a diacetyl rest with Wyeast 34/70, you can wait for a day or two after the high kraeusen (the peak of fermentation) subsides. This is usually indicated by a reduction in the activity of the airlock or a decrease in visible fermentation activity. Once the kraeusen has settled, you can then gradually raise the temperature of the fermentation vessel by about 5-10 degrees Fahrenheit (or 3-5 degrees Celsius) for several days.
This increase in temperature helps to activate the yeast and encourage them to reabsorb any diacetyl that may have been produced during the primary fermentation. The exact duration of the diacetyl rest can vary depending on factors such as yeast health and fermentation conditions, but typically a few days at the elevated temperature should suffice.
After the diacetyl rest, you can then lower the temperature back to the desired lagering temperature and proceed with the lagering phase of your beer. Lagering is the process of cold-conditioning the beer for an extended period, typically several weeks or even months, to allow for further clarity and flavor development.
In my personal experience with Wyeast 34/70, I have found it to be a reliable and clean yeast strain that produces excellent lagers. It has consistently delivered beers with a crisp and clean flavor profile, with minimal to no detectable diacetyl. However, it is always good to be cautious and perform a diacetyl rest as an extra measure to ensure the best possible results.
While Wyeast 34/70 is known for its low diacetyl production, it is still recommended to perform a diacetyl rest after the high kraeusen stage of fermentation. This rest involves raising the temperature of the fermentation vessel for several days to allow the yeast to reabsorb any diacetyl that may have been produced. After the rest, you can proceed with lagering your beer. Wyeast 34/70 is a great yeast choice for lagers, and with proper fermentation techniques, you can expect a clean and flavorful final product.