Open fermentation can yield some amazing flavors, but takes some special attention to temperature, cleanliness and fermenter shape. Most professional breweries that ferment in open vessels use coolships. Coolships are usually shallow rectangular shaped tanks with open tops. The idea is to maximize the surface area exposed for wild yeast and other microorganisms to land in. The shallow tanks allow for easy top-cropping (skimming) of yeast when it reaches high Krausen.

If you pay attention to your temperature control, ferment in a low traffic/low dust environment and use a shallow depth fermenter you should have no issues making a solid beer. A great spot to claim as your open fermenter's home is in a kegerator. You can completely clean and sanitize the interior, reduce the dust/particulate exposure and control the temperature. Once I get my fermentation going in a homebrew kegerator, I make sure to open the door a few times to allow fresh air in.

In the past, I have used shallow stainless steel buffet pans to open ferment with success. For this experiment I used the same methods I used when using the stainless steel pans, but I modified a 5 gallon whiskey barrel to act more like a coolship. I removed a few of the top staves creating a top opening to ferment a 2.5 gallon batch of Kolsch. An alternative would be to just pop one of the heads off the barrel and stand it on its side. This achieves an open fermentation, but your exposed surface area is smaller.

Here's what I used

1 5 Gallon Whiskey Barrel 2 Ratchet Strap 3 Rubber Mallet 4 Hoop Driver (Chisel) 5 Cleaner 6 Muslin (Cheese Cloth)

Here's what I did

Use ratchet straps to tighten up the barrel before removing hoops

Use a rubber mallet or hammer and hoop driver or chisel to lightly tap off the hoops.

Keep the hoops organized to reassemble later.

Loosen ratchet strap very slowly until you can pop up the staves on top.

Remove 6 to 7 top staves.

Put the hoops back on in the same order you removed them.

Clean exterior of barrel with PBW, then fill with 180F water. Soak 30 minutes and dump.

Fill the barrel with chilled fresh wort and (optionally) pitch yeast or allow only wild yeast from the air to innoculate your wort.

Cover the barrel with sanitized cheese cloth and place in a clean low traffic area.

Next Steps

Harvest yeast during high Krausen (if needed).

Rack to a closed secondary vessel once primary fermentation ends to reduce oxidation. I cold conditioned the Kolsch until clear at (38F), carbonated, kegged and served.