Coolship
Coolship (Anglicized version of the Dutch/Flemish koelschip) is a type of fermentation vessel used in the production of beer. Traditionally, a coolship is a broad, open-top, flat vessel in which wort cools. The high surface to mass ratio allows for more efficient cooling. Contemporary usage includes any open fermentor used in the production of beer, even when using modern mechanical cooling techniques. Traditionally, coolships were constructed of wood, but later were lined with iron or copper for better thermal conductivity.
Copper Coolship at a brewery in Prague
Homebrew Coolships
Many homebrewers will construct a "mini-coolship", as seen by Devin Bell's picture. The benefit of building one is that a ball valve can be installed near the bottom of the coolship, which will make transferring the wort easier. Another option that some people have reported trying is purchasing a large stainless steel pans from a restaurant supply store.
The third, and recommended option is to use your boil kettle. At the 2015 National Homebrewer's Conference in San Diego, James Howat's presentation, Wild and Spontaneous Fermentation at Home, showed that the surface area of smaller coolships is actually extremely more than large coolships used in production breweries [1].
- Example of a 36 bbl coolship:
- 10ft x 10 ft x 1.5ft.
- Wort volume = 1122 gallons = 150 cubic feet.
- Surface area of the top surface of the wort = 100 square feet.
- Surface Area to Volume ratio = 100/150 = 0.67 square feet of top surface area per cubic foot of wort.
- Example of a 10 gallon coolship:
- 2.5 ft x 2.5 ft x .020ft (2.4 inches).
- Wort volume: 9.35 gallons = 1.25 cubic feet.
- Surface area of the top surface of the wort = 6.25 square feet.
- Surface Area to Volume ratio = 6.25/1.25 = 5 square feet of top surface area per cubic foot of wort [1].
Surface area effects both the microbe collection and the cooling rate. Using a boil kettle, while it may still not be as close to the 0.67 sq ft/cu ft ratio as a production brewery coolship, will be closer than a "mini-coolship". James Howat also recommends perhaps trying to insulate the boil kettle so that the rate of cooling is not too fast [1]. For more information on the process of brewing with a coolship, see Spontaneous Fermentation.