Winter Warmers

It’s that time of year in the Northern Hemisphere. Leaves are turning color, pumpkin spice aromas are in the air, and brewers are dusting off their barleywine and imperial stout recipes in preparation for the winter season. Here are some tips and tricks for making the best high gravity beer:

Choose the right yeast

Yeast selection is much more important in high gravity fermentations. Look for a robust strain with a high stress tolerance. In most cases, we recommend choosing a very high attenuation strain. High attenuation is the result of a high affinity for maltotriose. At high gravity, all strains start to lose their ability to metabolize maltotriose, resulting in a lower attenuation. Choosing a strain with very high attenuation to start with will help to make sure the final beer is not too sweet. Maltotriose negative strains (many English strains) should generally be avoided. While these strains are stress tolerant, the low attenuation characteristics combined with a high gravity wort will leave you with an overly sweet beer.

Pitch enough yeast

Yeast does not divide very efficiently in high gravity fermentations, so it is important to increase the pitch rate according to the starting gravity. Use our Pitch Rate Calculator as a guide. In some extremely high gravity situations, the recommended pitch rate may be above the average rate of 0,5 to 1g/ L for most strains. This is normal.

Nutrition

A high gravity all-malt wort will usually have enough FAN to support the fermentation, but zinc may be lacking. Zinc is important to support yeast growth, which is inhibited by high gravity. It also serves as a co-factor for enzymes involved in alcohol production, so zinc levels are particularly important to support these enzymes in the late stages of fermentation of high ABV beers. If you are using sugars to boost your starting gravity, a balanced yeast-derived nutrient will help to provide FAN in the form of amino acids and peptides to support the yeast.

Oxygen

Oxygen is less soluble in high gravity worts, so make sure to aerate your wort well. You can also consider an aeration step after 24 hours to support the yeast. For dry yeast, aeration is not normally required, but it should be considered for high gravity fermentations when oxygen requirements are higher.

Use sugars and add mid-fermentation

Since sugars are 100% fermentable, they will increase your ABV level without adding body to the beer. The resulting final gravity will be lower, and the attenuation will be high. While many brewers take pride in brewing all-malt beers without adjuncts, high gravity is a situation where sugars should be more strongly considered to avoid beers that are cloyingly sweet. If using sugars, consider adding them after 24–48 hrs of fermentation. This allows you to lower the original gravity at the start of fermentation, which reduces the osmotic shock on the yeast and will allow for a faster start to fermentation. This approach usually also results in faster total fermentation, greater attenuation, and higher alcohol yields.

Stuck fermentation: Prevention and response

Stuck fermentations and under-attenuation are more likely in stressful high gravity fermentations. You can prevent stuck fermentations by paying attention to strain selection, pitch rate, and nutrition, as described above. Additionally, you could increase wort fermentability by using a lower mash temperature (60–64 °C, 140–147 °F) and longer mash time (60–120 min). In the event of a stuck fermentation, you could try re-pitching more high-performance neutral dry yeast such as LalBrew® House Ale or LalBrew Nottingham™. Use a pitch rate of about 0.5 g/L. Dry yeast is ideal for this purpose since it does not require aeration, which can cause off-flavors if done late in fermentation.

Be careful though – not all cases of low attenuation are due to poor yeast performance. It is possible that low wort fermentability is the issue. If there are no more fermentable sugars to ferment, there’s nothing more the yeast can do.

You may still be sipping the last grapefruit radlers in your fridge. In no time, you will be drinking fine, strong ales and imperial stouts to warm your palate. Cheers!