Sometimes, you’d like to produce more beer than you have the capacity for. Maybe there’s a party coming up or maybe you’d just like to squeeze a bit more volume from your setup. If fermenter space is your limiting factor, there is one thing you can do to expand your output — practice high-gravity brewing.
The Basic Idea
The basic idea behind high-gravity brewing is to brew a higher-gravity version of your intended beer, then dilute it to your target strength in the bottling bucket or keg. This technique comes from the “big guys” and is used to make every American-style Pilsner on the planet. (But don’t let that sour you on the technique, it works for many kinds of beer.) American-style Pilsners are commonly fermented from 16 °Plato worts (around OG 1.064), then diluted so that the “virtual OG” is around 11 °Plato (OG 1.044). If you followed this procedure at home, you could make 5.0 gallons (19 L) of beer with an OG of 1.064, then dilute it to 7.3 gallons (28 L) of beer that tastes like an OG 1.044 beer.
High-gravity brewing is sometimes euphemistically called blending for volume and it is used to expand the capacity of a brewery beyond the volume of it’s fermenters.
When the topic comes up on internet forums, many homebrewers will chime in to say that this technique produces “watery” beers, and cite American Pilsners as proof of this assertion. They are wrong. American-style Pilsners are brewed to have a light body; this is not simply an outcome of the technique. Even though you add water in the process, you will not end up with “watery” beer unless you try to make a highly-attenuated brew.
Think of this way. Let’s say you normally brew a porter with an OG of 1.048 (12 °Plato) and ferment it with a yeast strain that gives you 75% apparent attenuation, so your FG is 1.012 (3 °Plato). Now, let’s say you instead brew a high-gravity version of the porter at OG 1.058 (~14 °Plato) and it ferments to FG 1.015 (75% attenuation). If you dilute to a virtual OG of 1.048 (12 °Plato), the actual FG becomes 1.012 (3 °Plato) — same as it was when you brewed your porter at working strength. If you plan to brew a beer using high-gravity brewing, it’s body will not be less because you used this technique. (If you simply water down a beer that was brewed at working strength, then yes, it will taste watered down.)
The Problems (and Solution)
There are two problems associated with high-gravity brewing. As the specific gravity of wort increases, the beer fermented from it will have more esters. In fact, the increase in ester production is greater the increase in wort gravity. So, even though high-gravity beers get diluted, they resulting beer is more estery than if they were brewed at working strength. The solution to this problem is to limit the specific gravity of the strong beer to a reasonable level, given how acceptable esters are in your target beer.
The second problem with high-gravity is brewing is that water contains dissolved oxygen. If you diluted beer with regular water, the oxygen in it would prime the beer to so stale faster. In commercial breweries that use this technique, they have special equipment to produce deaerated water. As a homebrewer, you will have to rely on a more low-tech solution — boiling. Water that has been exposed to air reaches an equilibrium value of about 9 ppm dissolved oxygen. Boiling water reduces the oxygen level to around 1 ppm. (Commercial de-aerated water is usually less than 50 ppb — much lower.) So, if you boil water for about 15 minutes, then rapidly cool it, the level of oxygen will be very low. (It takes awhile for oxygen to dissolve back into the cooled water.)
In addition, unless you filter your homebrew, there will be yeast in your beer that will likely scavenge at least some of the oxygen. Also, it takes time for beer to go stale; if you are brewing for a party, the beer may all be consumed before the problem arises.
Tomorrow, I’l cover the practical aspects of high-gravity brewing. I’ll discuss how to formulate recipes for high gravity brewing and how to perform the “blending” on typical homebrew equipment (bottling buckets and Corny kegs). I’ll also talk about opportunities to yield more than one brew from a single batch; for example, maybe you ferment 5.0 gallons (19 L) of an English-style IPA, bottle a little less than gallon (~3.5 L) as the IPA and dilute the rest so you have 5.0 gallons (19 L) of ESB in your keg.
High-gravity brewing is not a technique you will likely use for every beer you make. However, it does come in handy when you need a lot of beer quickly. I’ll also discuss how to do this in your home brewery and the best styles or combinations of beers to brew with this technique.