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Risky to Top Off Beer in Carboy

April 02, 2012 | Comments: 0 | Views: 168

I stumbled upon a forum post in which the poster asked if he should use tap water or bottled water to top off the beer in his carboy during secondary fermentation. Apparently someone informed him that it was necessary to "top off," or raise the level of beer in the carboy, to reduce air space and limit the amount of oxidation that will occur.

One response to the post stated that some people use glass marbles to displace the beer, thereby raising the level, instead of adding water. As a home brewer since the late 1990s I've never heard of such a thing, nor have I read about it in any home brewing book or magazine.

Is It Necessary? During fermentation yeast is consuming sugars, producing alcohol and Carbon Dioxide (CO2), and a lot of it early on, so the amount of regular old air present in the fermenter is minimal. And since the CO2 is emanating right from the fermenting beer itself, there will be a layer of that gas along the surface of the liquid, so no real oxidation can take place during the fermentation process.

When you rack your beer to a secondary fermenter the process will continue at a slightly lower rate, but CO2 will still take up space in the fermenter and remain as a buffering layer above the liquid, ultimately preventing any substantial oxidation.

If your airlock is bubbling, even infrequently, there is CO2 being formed and positive pressure in the fermenter, so there is no need to top off the beer. If you find that your ending up with less than five gallons when making a five gallon batch of beer you need to plan ahead, not add plain water later. During a 60 minute boil I typically lose about 1 quart due to evaporation. Expect to lose more to absorption if you're doing a partial mash or all grain.

For extract brewers doing a concentration and blending with 3 gallons of cold water in the fermenter, it's a good idea to start your boil with an extra half gallon, just to be safe. You should not be needing to top off beer in the secondary fermenter to bring you up to 5 gallons, you should be fermenting at least 5 gallons to begin with, and it's a good idea to use a 6 gallon fermenting bucket or carboy.

It's Not Worth the Risk! The person who recommended topping off the fermenter to this home brewer may have been confusing the process of wine making with beer making. And he wouldn't be the only one; during a brief perusal of the web I found one blog published by a brewer who actually compared the two and suggested topping off beer in the secondary because he thought it made sense, since he does it for his wine.

The fact is, after primary fermentation a wine is racked to a glass carboy, degassed, and topped off to minimize oxidation before being left to settle for 30 days or more. This process involves mixing in sulfites which halt the fermentation process. Sulfites also acts as a preservative and can help reduce oxidation during long term aging in the carboy or in bottles.

Typically a commercial grade wine of the same variety is used to top off the carboy. This is the recommended practice, although water may be used in some instances. I use wine, never water.

The major difference is that the wine fermentation has been halted by the sulfites, and it sits in the carboy for about a month. Topping off is a good idea when it comes to wine production, and it will not adversely affect the wine because preventatives are present.

When racking a beer to the secondary fermentation is not halted, and no sulfites are added. The beer is typically bottled within 10 days of secondary, so reducing the air space in the carboy for beer production is not at all necessary, and is not a good idea! If you're worried about oxidation during long term conditioning in the bottle you can use special bottle caps which absorb the surplus oxygen.

Personally I recommend NEVER topping off beer in any fermenter, primary or secondary. The risk of contamination by adding water or pouring in glass marbles is greater than any potential oxidation that may occur in the first place. It's just not worth it. Leave the beer alone!

Drew Vics is a member of the American Homebrewers Association and has been home brewing since 1999, with extracts as well as all-grain. He has a background in graphic design and web design, and is also a songwriter and musician. He writes articles on beer brewing and other beer related topics at his website

Source: EzineArticles
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