Fermenting a high-gravity beer is always challenging due to high levels of alcohol, which are toxic to yeast cells, and monstrous amounts of sugars for the yeast to consume. This can lead to stuck fermentations, fusel alcohol off-flavours, and other problems. In this article, the team at White Labs share some quick tips and tricks to help you have a full, complete fermentation.
Pitching the right amount is crucial for all the fermentables to be eaten and converted into ethanol. Similar to not inviting enough guests over to a Thanksgiving party. If the ratio of guests to food is off, there will be leftover food.
In the context of brewing, not pitching enough yeast can lead to stuck fermentations, leftover fermentables, and overly sweet beers. Common pitch rates for high-gravity brews can range from 1–1.5 million cells/P/mL.
Oxygenate and Aerate
Brewers inevitably want to minimise oxygen in their process, with one exception: wort. In other aspects of beer production, oxygen has detrimental effects on flavour and stability, but the opposite is true in the early phases of fermentation.
Yeast depends on oxygen to provide the building blocks needed to synthesise fatty acids and sterols, essential components in the yeast cell membrane. It helps the transportation of sugars, pH, and metabolic by-products in and out of the cell. By having proper cell membranes, the reabsorption of acetaldehyde and diacetyl can be aided to convert into ethanol and acetoin.
Most texts will recommend a standard dissolved oxygen rate of 8–10ppm (mg/L) in a moderate gravity wort (up to 12° Plato). For a high-gravity brew, 1 ppm per Plato is a great place to start for oxygenation.
Supplement with Nutrients
Nutrients give yeast the necessary boost needed to complete fermentation. Like our daily vitamins, nutrients such as zinc, magnesium, and nitrogen.
From our previous research, fermentations with an added dosage (50g/BBL) of a Nitrogen-rich Nutrient (FAN-Max Bio) led to quickening fermentation timelines by reducing the time to final gravity by around 50% in both 22 and 25 Plato wort. It reached terminal gravity in record time meaning faster high ABV beer with a clean fermentation profile.
With these three simple tips, the risks of a stuck fermentation and an acetaldehyde taste are less likely to occur. Healthy yeast is still needed, and we recommend a later generation 3–5 as they are more accustomed to the requirements of fermenting a big beer.
Be diligent and monitor your pH drops and gravity timelines, where a rousing of yeast or other brewing techniques might be needed. Big beers don’t need to be intimidating. In no time, a big brewed beer can be on its way.
