OnTap Magazine

H omebrewing has never been more popular in South Africa and while the warmer weather probably has you brewing the likes of a crisp pale ale or for the more adventurous brewer, a low ABV sour, it’s wise to plan ahead for the coming seasons. Whether you’re allowed to buy beer or not, the best high gravity brews you’ll taste this winter are likely to be ones you make yourself. And since brewing such high gravity beers requires time, the moment to start brewing them is now. WHAT IS HIGH GRAVITY BEER? I really hate hair-splitting, so let’s not spend too much time arguing about what is or is not a high gravity brew. Generally, most brewers will agree that high gravity beers tend to push the envelope of a typical beer yeast’s capacity to create alcohol productively. In most cases, and for most yeasts, that would mean a starting gravity range of 1.070 - 1.100, with associated alcohol levels of around 7-12 % ABV. But the ambitious homebrewer need not be limited by conventional wisdom! Nowadays, and by using techniques perfected by extreme craft brewers like Sam Calagione from Dogfish Head Brewery, one can aim far higher and brew monster beers that can reach up to 18-20 % ABV. However far up the ladder of high gravity brewing you decide to climb, the techniques below will help you get there. SELECT THE RIGHT YEAST 1 ADD OXYGEN 2 ADD SUGARS GRADUALLY 3 Most homebrewers underestimate the humble ale yeast in its capacity to ferment high gravity beers. Thus misinformed, they may be tempted to always reach for a Belgian-style yeast that is known for its high gravity potential. And if you’re brewing a Belgian ale, by all means, use the right yeast (Lallemand’s Abbaye dry yeast, for instance, has an alcohol tolerance of up to 14% ABV). But what about brewing a high gravity IPA, or barley wine? These styles don’t necessarily call for the flavours that a typical Belgian yeast will produce. Fortunately, the average ale yeast will, given the right environment, happily ferment out beers to as high as 8-12% ABV. The caveat is just that though: given the right environment (more on that shortly). For higher gravity beers than that (i.e. 13-20% ABV), you should consider the more specialist, highly alcohol- tolerant, highly attenuating yeasts now available from most large yeast labs (often described as yeasts well-suited to barley wine production). Just be sure to use brewing yeast, please! Some brewers aiming for high ABV percentages think that champagne yeasts are a good idea. They are not. Such yeasts tend to produce super-dry beers by throwing the delicate balance between bitter (from hops) and sweet (from malt) seriously out of whack The result is often almost undrinkable. So, rather use them for their intended purpose: making bubbly. A final caveat: be sure to pitch enough yeast. For homebrewers who use dry yeast, this is not normally an issue, providing you use recently packaged yeast (within the last year or so). But for those of you who use liquid yeast, you will have to create more yeast cells for pitching by creating a yeast starter. A comprehensive explanation of how to build a yeast starter is not the topic for today, but here’s a short version: boil some dried malt extract to create a litre or two of wort, pitch the liquid yeast into this, let it grow for a day or two, then pitch into your brew. Oxygen is generally not a good addition to beer. But there is one exception: when you pitch your yeast. Adding as much oxygen to the wort as possible will really boost your initial fermentation and give your yeast a fighting chance in this high gravity environment you’ve created. You can do this by vigorously shaking the wort inside the fermenter before pitching, or even better, oxygenate using a tank of oxygen or air and an If you are a regular reader of this column (thanks for that!), you’ll know that I’ve mentioned the issue of yeast health quite a few times (in fact, I dedicated an entire article to the topic back in the winter 2018 issue). But high gravity beers pose several challenges to yeast health. Not only are high concentrations of alcohol toxic to fungi like yeast, but the massive amount of solutes (i.e. fermentable and non-fermentable sugars) in high-gravity wort results in aggressive gradients of osmotic pressure (i.e. the tendency of solvents to move through semi- permeable membranes from a low to a high concentration of solutes – are you still with me?). This in turn disrupts the normal metabolic processes in yeast and can result in cell death or shock (and a stuck fermentation). So, rather ironically, the fermentable- rich wort of a high gravity brew does not give yeast a very good prospect for survival. The issue is further compounded by the frequent additions of sugars like Belgian candi sugar to the list of fermentables to boost the gravity of the brew. And while reaching ABVs of 7-12 % is reasonably attainable by adding a moderate percentage of such sugars to your boil, going higher than that while still maintaining yeast health becomes problematic (for the reasons mentioned above). The solution? You have to limit osmotic pressure and initial alcohol levels by keeping the starting gravity of your beer below 1.100. But, I hear you say, that will only result in a beer with ABV of around 12 % (assuming a typical final gravity of say, 1.010). The way to go beyond this barrier is to add your adjunct sugars during fermentation and not in the boil. Fortunately, most sugars are relatively resistant to bacteria, but if you’re worried, sterilise your sugars by boiling them in a small amount of water. Adding sugars gradually throughout the primary and secondary fermentation stages of your beer will allow for a gradual ramping up of alcohol while at the same time restricting massive osmotic pressure differentials. All of this will in turn contribute to keeping your yeast happy and healthy. High gravity beers tend to push the envelope aeration stone similar to those used in home aquariums. Running the aeration stone for about an hour or so just after pitching your yeast should do the trick. ontapmag.co.za | Autumn 2021 | 53