I always see people mentioning beer in their chum recipes. Most of the beer we all drink is highly pasteurized, with no trace of live yeast culture. Unless you are using some expensive, micro-brewed, live-yeast beer; pouring a 12 ounce can in your bucket isn't going to do anything but waste beer.

If you are trying to make chum in a short amount of time, add a cup of sugar and a package of baker's yeast. This should get the mixture fermenting within a few short hours. However, if you are making your chum a month or more ahead of your trip; do like Standalone said "water, maze and time."

Yeast is a fungus. As such it needs sugar, water and oxygen to reproduce. Any grain you use has very little sugar content. What it does have is a complex carbohydrates, starch and fiber. Naturally occurring bacteria will produce enzymes - namely amylase - which will break down the starch into sugars that the yeast can act on. One of the best sources of these naturally occurring bacteria is moldy bread. You can also purchase amylase from brewing supply stores and from Amazon. It's pretty cheap and you don't need very much.

Also, I see a lot of guys talk about burping the bucket, or leaving it open all together. At first you do want to leave the bucket open. The exposure to atmospheric air allows for bacteria and yeast to colonize the mixture and for these organisms to reproduce rapidly with oxygen. However, after vigorous fermentation subsides - usually with 48 hours - you want to close your bucket up tight. In a short period of time the yeast will use up all the remaining oxygen in the bucket and begin anoxic fermentation. During anoxic or ammonia fermentation, yeast and bacteria produce chemical byproducts such as Butyric acid. Butyric acid is an amino acid that is associated with the smell of human vomit and stinky cheese. Cheese is loaded with Butyric acid. Catfish are extremely sensitive to amino acids, including Butyric acid. This is exactly why cheese-based baits work so well.

I realize that I probably just went way too deep into the manufacture of chum. You'll have to excuse me. I'm a chemist by trade, studied marine science and oceanography at Texas A&M and one of my hobbies is catfish chemo-sensitivity research.

Anyhow, grain, water and time are all you really need. Nature will do the rest. If you want to speed it up add some sugar, amylase and bakers yeast.