Carboys are glass jugs, much like water cooler bottles, that brewers use for making beer, wine, hard cider & mead. They come in a range of sizes, from 3 gallon to 6 gallon. A glass carboy does not allow oxygen to pass through and change the beverage inside. The effects on oxygen on beer, wine, mead and cider, after fermentation is over, can be tasted and smelled. Most brewers and drinkers agree that these are not positive. Carboys will , with careful treatment, be usable for a very long time.
Using a carboy as a fermenter
Carboys need to be sanitized. A solution of one tablespoon of bleach/1 gallon of water makes a great sanitizer. Carboys will not absorb any bleach aroma and can be filled in advance.
I take advantage of a sanitizer filled carboy to sanitize my wine thief/hydrometer. Just stand it up in the carboy, then rinse.
A carboy used as a fermenter should have some headspace. A 6-gallon carboy is usually a fermenter for up to 5 gallons of homebrew.
You will need some accessories for your carboy:
special brush to clean it
handle (install under the lowest bump on the neck)
a milk crate (handy for moving carboys and keeping them off rough floors, like concrete)
Be careful not to place a filled carboy on a surface that is not totally clean and smooth. You don’t want to create any pressure points that could crack the glass. You can set the carboy on a flattened piece of cardboard or on a towel/rug.
When fermentation is underway, you may not have enough headspace. Foam can potentially clog the stopper/airlock. When that happens enough pressure can build up to crack the carboy. The orange cap in the picture is attached to a 3′ piece of 7/16″ tubing that is submerged in a jug of water. Any foam will exit this way and end of in the jug. When the foaming stops you can leave the blow-off in place or exchange it with a stopper and airlock.
Always strain out whole/leaf hops when you ferment in glass. Hops that don’t clog the stopper or blow-off will end up clogging your racking cane. Bummer.
A stick-on thermometer is a great accessory. Place it below the three gallon mark, and you can see the temperature as you top it off. You can then change the temperature of the water to hit your target pitching temperature.
Keep your beer covered when it is in a clear container. UV light hitting the hop oils will produce an aroma that is unmistakably “skunky” . A paper bag with a whole cut in the middle of the bottom works well. T-shirts and zip up hoodies are stylish, too.
Using a carboy for secondary
The term secondary fermenter can be a bit of a misnomer. When used in brewing, most, if not all, fermenting should happen in the fermenter. But sometimes there will be some fermentation happening slowly so a carboy with an airlock is the best place for that to happen. Not all beers need time in a secondary. If you are learning to brew or brewing an ale with less than 5% alcohol, the secondary is entirely optional. Typically these are the styles of beer new brewers get started on so basic brewing kits don’t always include this equipment. However, there are some styles of beer that really need time in secondary to come out their best: higher alcohol, over 5-1/2% ales, all lagers, brews that you want to oak or add other things to or beers that you plan to keg.
Other benefits, for all beers, are:
Less sediment in the bottom of the bottle
Less chance of yeast autolysis occurring, where the poor starving yeast starts to cannibalize the other yeasts cause you aren’t feeding them
Better, more consistent carbonation. Sometimes, when fermentation is over, there is still some C02 in the beer that hasn’t yet moved out of the beer and airlock. When you prime a beer that still has some gas in it, you might end up with an overcarbonated brew
A head start on conditioning. You brew is “born” on the day it is done fermenting. You will hear us talk about conditioning and whether or not a brew is ready to drink. All beers need time after fermentation is over to mellow and mature. When you bottle directly from the fermenter then the carbonation and the clarifying/settling out will mostly be done in the first two weeks. The beer is ready to drink and you will probably notice the brew tastes better and the head retention will improve during the next 4-6 weeks. If you let your brew have more time in the carboy, the clarifying and conditioning will happen there and when you do bottle or keg, you’ll have more, better conditioned brew.
You can schedule bottling or kegging when it is convenient for you. As long as it has had a week or two, bottle when you want.
You should use a carboy for secondary that you can fill up. If you make five gallons of brew, use a five gallon carboy for secondary.
You can have it filled with sanitizer ahead of time. I like to rack the sanitizer I use on brewday to fill the carboy that I’ll be using later on. It keeps sanitizer going through my siphoning equipment and doesn’t waste sanitizer.
Keep the carboy covered or in a dark place. Light hitting the beer will create an unmistakeable skunky aroma.
Don’t forget to check the airlock when you are doing a long term secondary.