Dear Mr. Wizard
I've been homebrewing for approximately four years now, and to this day it remains my primary obsession. I've wanted to get into brewing some high-gravity beers such as barleywines and imperial stouts. I've read quite a few articles on high-gravity fermentation, but I still have a number of questions I was hoping you would be able to answer for me.
- I've read that pitching a strain of champagne yeast after racking to the secondary will assist with the full attenuation of the beer to the desired alcohol level. Is this a recommended procedure? If so, wouldn't you need to re-oxygenate your beer again in order for the additional yeast to begin fermentation? If so, wouldn't the addition of oxygen at this point cause some considerable off-flavors? Is champagne yeast the strain to use or should you pitch some additional alcohol-tolerant ale yeast? Also, is it necessary to build another starter for this procedure?
- I've seen many recipes for high-gravity beers that indicate quite extended primary and/or secondary fermentation schedules (some two to three months). I would surmise that after such extended fermentations, most of the yeast will have settled out of suspension. Some of these recipes recommend pitching an additional smack pack of your original yeast at bottling to ensure adequate carbonation. Is this practice usually necessary and is it safe (i.e. exploding bottles)? Again, wouldn't you need more oxygen for the yeast to go to work? I would guess that this procedure may also be recommended prior to bottling after extended lagering at low temperatures. Would you recommend doing this along with adding more yeast to the secondary as discussed above? Your enlightenment on these issues would be greatly appreciated.
Mr. Wizard replies:
There are several schools of thought on high-gravity fermentations and how best to ferment all of the fermentables in the wort. The idea that appeals to me the most is based on some very simple principles. I answered a rather similar question in the last issue of BYO (February '00) but there are a couple of points you raise that I didn't address.
My basic philosophy with high-gravity beers is pretty simple. Pitch enough yeast, aerate the wort well and get on with it! Most brewing strains can handle wort gravities up to about 1.080 without much problem and many will work fine with worts up to about 1.100.
In response to your question, I would personally never add more oxygen to fermenting beer - period. Adding more yeast, on the other hand, is often beneficial when fermenting a high-gravity wort. Additional yeast is also frequently added to beer following very long aging periods prior to bottling. This practice is safe as long as the beer is completely fermented when it is bottled; it's really no different than normal bottling.
It is important to understand that yeast does not require oxygen to ferment; rather it needs oxygen to multiply - oxygen is required by yeast cells to synthesize sterols and unsaturated fatty acids that are used to build new cell walls. Fresh yeast that comes out of a propagation step contains an excess of these cell-wall-building compounds and is capable of limited multiplication in the absence of oxygen. When wort is first pitched after cooling, it is very important that the wort is aerated because the excess of sterols and unsaturated fatty acids is insufficient for the intensive growth in the early stages of fermentation.
A similar method used by many brewers to help finish a fermentation is to add a portion of actively fermenting beer to a slowing fermentation. This technique of "kraeusening" is traditionally used as a method to carbonate lagers but can also be used to solve other problems. With or without kraeusening, lagers are carbonated during aging because they are aged under pressure. For this reason high-gravity lagers, like doppel bocks, are allowed to naturally clarify during their long lagering period without having to worry about bottle conditioning. All traditionally aged commercial lagers employ this method, but most homebrewers treat ales and lagers the same when it comes to carbonation. If you use a traditional lagering method, there is no need to add more yeast before bottling, although you will need a counter-pressure bottle filler.
Some fermentations begin to slow down toward the end because of premature flocculation of the fermenting yeast. A simple technique to keep these sorts of fermentations on track is to "rouse" the fermentation. In a commercial brewery, rousing may involve transferring the beer to another fermenter or pumping the beer around in the fermenter to mix it up, but at home rousing is simple - just gently rock your carboy or fermenting bucket and the fermentation has been roused!
Like I said, I don't like to aerate beer during fermentation, but this answer would be incomplete if Yorkshire stone squares were not mentioned. Yorkshire stone squares are a type of fermenter developed in Yorkshire, England. Sam Smith's in Tadcaster is famous in the United States for its use of stone squares, although it has been reported that Sam Smith's no longer uses this technology. A Yorkshire square is an open fermenter with two chambers separated by a deck and connected with some tubes. The center of the deck has an opening that flares upward to allow the fermenting beer to spill up onto the deck.
The key feature of a square is a recirculation device that actually pumps the beer from the lower chamber and sprays the beer through a device resembling a shower-head onto the shallow deck that separates the upper chamber from the lower chamber. The beer in the upper chamber flows back into the lower chamber through tubes called organ pipes. These things sound really strange when described - it's no surprise they were invented in merry old England. The pump-over simultaneously rouses and aerates the fermentation. This technique works for the brewers that use it and there are some really nice beers made using this method. One of the side effects to aerating a fermentation is abnormally high levels of diacetyl; that's a trait of beers fermented this way. If all else fails, aerating your beer during fermentation will not be the end of the world. You may even be pleasantly surprised with the resulting beer!
Mr. Wizard, BYO's resident expert, is a leading authority in homebrewing whose identity, like the identity of all superheroes, must be kept confidential. To see more of Mr. Wizard, check out the latest issue of Brew Your Own available at better homebrew shops and newsstands.