Fermentation tips for High Gravity Beers

When brewing high gravity beers (beers with an original gravity of 1.064 or higher) there are a few common faults that crop up in a homebrew setting:

- Higher alcohols that give a solvent like aroma and taste to the beer. This is caused by yeast stress, such as too few nutrients and by too high a fermentation temperature.

- A high finishing gravity, this is caused by the yeast dropping out early, insufficient pitch rate and nutrients, alcohol intolerance, or temperature swings.

I find that when making these high ABV beers many homebrewers place too much emphasis on getting the brewing side right (recipe, mash times, temps etc) and neglect some of the fermentation side activities that can have the biggest impact on your beer.

The challenge is creating an environment for the yeast to have the best chance of success. Effort is required in both planning, selecting the right strain(s) of yeast, and throughout fermentation, providing proper aeration, nutrition and temperature for the yeast to reproduce and grow. Below are some tips and techniques that I’ve utilised over the years to help me consistently craft a truly great quality, homebrew scale, ‘big beer’.

 

Yeast:

A lot of standard beer yeast strains (both liquid and dry) that we stock will get you to 10-12% ABV if the fermentation conditions are correct. For very high gravity beers above this you will need something specifically for this such as White Labs Super High Gravity Yeast - WLP099, which has a stated alcohol tolerance of 25%. With strains like this you can use them singularly, or use the regular yeast that you want to use to produce the dominant flavour profile (In the first 72 hours of fermentation most flavour compounds are formed, adding yeast later than 72 hours is unlikely to add to the flavour and aroma of that beer), and then pitch WLP099 when fermentation is 2/3 complete.

Ideally this would be pitched from an active fermenting starter that’s using the same wort as the main beer.

Pitch a big starter, I’d recommend at least 1.5x what you would normally pitch for the given OG, at least 1.5 mil. cells/ml/°Plato is the usual rule of thumb I work to.

If the yeast falls dormant before the job is done you can rouse the yeast back into suspension and wake them up to finish the job. Use a sanitized spoon or racking cane to stir up the beer and sediment to get the yeast back in suspension and in contact with any unfermented sugars. Don’t be tempted to use a wine or champagne yeast to finish out fermentation, such yeast could finish too dry, leaving your beer without the desired flavours available from beer yeast. 

If you’re not sure on the strain(s) to use for the specific high ABV style you’re looking to produce, please don’t hesitate to give us a shout and we’ll happily point you in the right direction.

 

Pitch and Fermentation Temperature:

 

Keep fermentation temperature low, especially in the early stages. Typical temperatures recommended by Wyeast for their high-gravity yeasts are 18–27 °C and those from White Labs are in the 18-24 °C range. I go for the low side of these, starting with the fermentation temperature around 18–19°C at the outset and monitoring it throughout.

 

The high level of yeast activity will easily push the beer up 5-7°C above start temperature during the first few days of fermentation, which if you’re already on the higher end will cause those harsh fusel alcohols to be produced. As fermentation slows, allow the temperature to increase towards 24-27°C to ensure the yeast doesn’t drop out before the target FG is reached.

 

Oxygenation / Aeration:

 

As the concentration of the wort increases, so does the need for oxygenation. Because yeast needs oxygen to do its work, it’s really important to keep oxygen levels up, particularly in the first 24 hours after fermentation starts. The solubility of oxygen in wort decreases with gravity, so unfortunately shaking the wort before pitching is not enough.

I aim to oxygenate every day up to the point of high kräusen or each time sugar and yeast nutrient are added. You can use aquarium stones or compressed oxygen cannisters for oxygenation. I find that just 2 minutes with oxygen, or 10 with air has the desired effect. Saturating the wort with pure oxygen has the added benefit in of making the yeast walls stronger and therefore more tolerant to alcohol.

Agitating the wort regularly also helps, the work involved shaking your full fermenter is worth the physical effort. It helps to deliver nutrients that the yeast needs right to the cell wall, keeps yeast from flocculating, and eliminates carbon dioxide, which is toxic to yeast. I again do this to high kräusen, after this point additional aeration during fermentation shouldn’t be necessary if a sufficient quantity of yeast was pitched at the start of fermentation.

pH Levels:

 

I use brewing salts and acid to adjust the wort pH to between 5 and 5.4 (We'll cover this in more detail in a future post). With proper aeration and the addition of nutrients, it should remain between 4 and 5 during fermentation, dropping slightly as it nears completion.

 

Additions:

Supplementing yeast nutrients such as these will reduce lag time, improve viability and help provide consistent attenuation rates. I will add yeast nutrients (ideally a blend containing micro-nutrients as well) at 3 stages, to the boil, to the yeast starter to promote growth and then again to the primary at the start of fermentation. This really helps big beers reach their terminal gravity. Yeast nutrients should not be added once the beer has achieved about two-thirds of the total expected attenuation.

I have also used enzmyes like this dry beer enzyme that ferments normally un-fermentable dextrins. This can be added at the start of fermentation, or if you’re beer has unexpectedly finished too sweet, stir gently into beer and fermentation should start again in 24 hrs and continue to dryness.

Another technique that works well with high gravity Belgians is introducing sugar slowly instead of putting it all in at once. Start with just the malt and then add Belgian candi sugar slowly, putting a little bit in every day or so. The sugars will re-awaken the yeast and be converted to alcohol, boosting the gravity and adding further complexity to your flavour profile.

If you have any further tips that you use when brewing high gravity beers please add them in the comments below.