Wort aeration is an extremely important step in homebrewing that is more often than not completely over-looked by extract brewers. The fact of the matter is that one of the best ways to prevent fermentation problems is to ensure that your wort is well aerated. For even though yeast doesn’t require oxygen in the latter stages of its life, it is vital to growth and reproduction, and thus vital to good beer, that plenty of oxygen be on-hand in the earlier stages.

When to Aerate

There are basically only 2 rules to aeration :

  1. Do not aerate when the wort is too hot. A cooler wort will accept a lot more air than a warmer one, so it is to your own benefit to wait for it to cool down before aerating. There is also the much-debated issue of hot-side aeration, which could cause off-flavours in your beer. What happens is that when you aerate hot, oxygen binds to certain compounds in the wort so the yeast cannot consume it as it normally would. It can stay bound for several weeks to several months before unbinding again. Once unbound the oxygen does to your beer what it does best : oxydizes. So you want the wort to be as close to room temp as possible when you aerate it.
  2. Do not aerate after fermentation has begun. It is fine to aerate right after pitching the yeast. Indeed, that’s exactly what many people do. However, once fermentation has begun, it is gernerally considered bad for the beer to introduce any oxygen. Though realistically the young beer can benefit from the introduction of fresh oxygen at very least for the first 5 or 6 hours of fermentation, and probably twice that.

Another possible exception to the above rules is that occasionally aerating the wort is the only way to get things going again if your fermentation sticks. Of course, a stuck fermentation is often a sign that the wort wasn’t aerated properly in the first place, or that you messed something else up, so keep good notes and remember that a bit of preventative medicine goes a long way.

Agitate the Carboy

It is possible to get a good aeration without any special gadgets or equiptment other than your standard carboy. When we used a 23l carboy as our primary, we would aerate simply by filling the carboy about three-quarters to four-fifths, corking it, then tipping it over slightly to one side and vigorously rocking it back and forth. This rocking should continue for 10 to 15 minutes, and can be done as 3 five minute intervals, as it otherwise may become very tiring.

Dumping 2 Buckets

Our favorite means of aeration is by dumping the unpitched wort between 2 large white food-grade buckets until the head of foam is too big and you risk overflowing the bucket. It’s easy and fool-proof, and fits with our “no muss, no fuss” style of brewing.

Aerating Yeast Starters

When dealing with small amounts of wort (500ml to 1000ml), like when using yeast starters, it is possible to aerate the wort by dumping it back and forth between two well-cleaned and sanitized mason jars. Just pour it back and forth 10 or 15 times, and you’ll have a well-aerated wort.

Using a Chiller

Another method of aeration that works really well can be employed when using a counter-flow wort chiller . You simply take the wort-out hose from the chiller and barely stick it into the top of the primary fermenter, letting the outflowing wort cascade down into the primary. If you have a good rate of flow through your chiller, you well get excellent aeration with this method.

Use an Airpump

An even easier way to aerate your wort is with a cheap fish-tank air pump and aeration stone. Although many people use this without the addition of any sort of in-line air filter, I recommend the filter. It is cheap, and easy to make.

In-line Filter

I bought 2 medical syringes (5cc) at the drug store for 30 cents each, then bought some white fish-tank filter material and some (really teeny-weeny) carbon at a pet store. I loosely stuffed the white stuff in each syringe to fill it almost half way, then poured in the carbon to fill half of the leftover space, then plugged that up with more of the white stuff. Be careful not to pack the white stuff in, though, as you’ll block the air-flow. Just putting it in loosely will be fine. Then I took plumber’s tape and connected the 2 syringes together back-to-back.

Then taped over that with regular clear packing tape. The hose from the air pump fits perfectly and snugly over the ends of the syringes. Also, I saved the end-caps from the syringes so that I can remove the filter and cap the ends for storage.

There is enough filter material left over to last me a long, long time, as well. So all I’ll ever possibly have to buy is more syringes.