Yeast Selection, Dry Yeasts, and It's Impact on Gluten-Free Brewing
One of the most important, yet often overlooked, aspects of developing a beer recipe is selecting the yeast. Before we fully dive into this topic, it is important to make sure that the yeast you select is gluten-free.
SELECTING GLUTEN-FREE YEAST
Many yeasts are cultured in a gluten containing medium, such as wheat, barley, or rye. Although it is possible to get gluten-free liquid yeasts, to our knowledge, they are not readily available to most homebrewers. Be careful of the notion that liquid yeasts are ok because the yeast culture is a small component of the finished beer, rendering the finished beer below a particular ppm limit. This is a very slippery slope. In our opinion, it is best to stick to naturally gluten-free ingredients, particularly for the homebrewer.
Gluten-free homebrewers generally must use dry yeasts to ensure that they are gluten-free. Dry yeasts have come a long way, and you will still be able to make a great tasting beer. More importantly, if you do your homework on the yeast and the medium it is cultured in, you can make a great tasting beer that will not make you sick. For dry yeasts, we have had success with Danstar (Llallemand), Fermentis, and Brewferm. Danstar and Fermentis in particular have a wide variety of dry brewing yeasts that they indicate are gluten-free.
YEAST AND ATTENUATION
Manufacturers provide a lot of information about their yeasts. One piece of information that you will find is attenuation. Remember that yeast consumes sugar to produce alcohol and carbon dioxide. Attenuation refers to the percent of sugar consumed by the yeast. Sugar levels are generally measured by gravity, which we posted about in February 2013 post.
Attenuation (%) = (Original gravity – final gravity)/(original gravity) x 100
Now that we have an understanding of attenuation, lets bring this back to selecting yeast. In beer, sweetness from residual sugar is generally balanced by bitterness although in some cases, sweetness may balance sourness (for example, in a fruit beer with a citric fruit). Understanding attenuation is important because it will help balance out the bitterness (or perceived bitterness) of a beer or make the beer seem sweeter or more crisp or dry.
You can usually find either a percent attenuation level or qualitative description of attenuation on the manufacturer’s website. For example, here are the qualitative descriptions from Danstar:
- High attenuation: Nottingham, Belle Saison
- Medium to high attenuation: Munich, BRY-97 American West Coast
- Moderate attenuation: Windsor
While attenuation is only one consideration for yeast selection, different levels of attenuation will produce considerably different beers. For example, say you were brewing a gluten-free brown ale with a British ale yeast and OG of 1.05. You could select either the Nottingham or the Windsor from the Danstar line. The Nottingham would finish at around 1.010 FG and an ABV of 5.25% (depending on process and ingredients). The Windsor would finish around 1.018 FG and an ABV of 4.2% (depending on process and ingredients).
All things being equal, the Windsor will produce a brown ale that is perceived as much sweeter and less bitter and the Nottingham will be perceived as less sweet, and potentially more bitter. Aside from impacting perceived sweetness and bitterness, the difference in attenuation will also impact perceived body and mouthfeel. Increasing the alcohol content in a beer generally increases the perceived body; whereas, residual sugar can also contribute to perceived body.
Although this post may be a bit heady, we hope that it helps you design better gluten-free beers through the process of yeast selection and balancing your beers.