Coolship

Copper Coolship at a brewery in Prague

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.

Homebrew Coolships

Miniature Coolship by Devin Bell

Boil kettle coolship by Gail Ann Williams. Cheese cloth was used to keep out debris, and a chair was carefully placed to keep out wild raccoons.

(This section in progress.)

Many homebrewers will construct a miniature coolship, as seen by Devin Bell's picture. Devin has reported good results from using his miniature coolship . 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, as well as food grade plastic trays.

The third 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, brought up the issue of surface area to volume ratio . The surface area to volume ratio of a hot liquid, directly affects the cooling rate of that liquid (it affects the cooling rate of all objects, not just liquids) . In other words, the greater the surface area of a given volume of liquid, the faster it cools. For example, imagine 100 liters of hot liquid is in a very wide and flat container. It will cool much faster than if it was in a perfectly square container, and even faster still than if it was in a spherical container. See this article for another explanation of how surface area to volume ratio affects cooling.

Surface Area to Volume Ratio Example

James Howat's example of how to find the surface area to volume ratio of a coolship is found below. Note that this example is not a true surface area to volume ratio equation, but a simplified version that only measures the top surface of the coolship. It makes sense to only consider the top surface of the coolship since most of the heat will escape from the uncovered top of the coolship. A true surface area to volume ratio would show an even larger difference between the two example coolships below . Additionally, this example shows that the surface area to volume ratio is not linear across vessel sizes.

Example of a 36 bbl coolship:

Dimensions of the example coolship: 10 ft x 10 ft x 1.5 ft.

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 per cubic foot.

Example of a 10 gallon coolship:

Dimensions of the example miniature coolship: 2.5 ft x 2.5 ft x 0.20 ft (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 per cubic foot.

The above example shows that the surface area to volume ratio of the 36 bbl coolship is much less than the surface area to volume ratio of the 10 gallon coolship, thus it will cool slower. A typical boil kettle (math not provided due to it involving circles) has dimensions that provide a surface area to volume ratio that is closer to the 36 bbl coolship (estimated 1-2 square feet per cubic foot). Further insulation of the boil kettle may help obtain a cooling rate that is comparable to the 36 bbl coolship. Other factors that influence the cooling rate of wort are the temperature between the wort and its surroundings, and what the thermal conductivity is of the material that the coolship is made out of.

Another factor that is affected by the surface area to volume ratio is the inoculation rate. The larger the surface area, the more microbes that are collected. However, it has been shown that the surface area to volume ratio of large commercial coolships is adequate for collecting microbes, so in theory this shouldn't be a concern for homebrewers . For more information on the process of brewing with a coolship, see Spontaneous Fermentation.

Editor's note: a discussion on the merits of cooling rates for coolships is worthy of a separate, in-depth analysis, and currently isn't covered here.

See Also

Additional Articles on MTF Wiki

• Spontaneous Fermentation
• Lambic

External Resources

• King's Coolship, BrewingTV Episode 42.
• Lambic and Wild Ale blog; Cool Ship posts.
• The Sour Hour, Episode 11 with Rob and Jason from Allagash, Jean Van Roy from Cantillon, and Vinnie from Russian River.
• Koelschip, Lambic.info.
• Amos Browne (Browne and Bitter blog) shows that not all coolship projects succeed.
• Amos Browne's second attempt (Browne and Bitter blog) with lessons learned from the first attempt.
• Slow Learning: Sour Beer Experiments, by Gail Ann Williams.
• Black Project's Coolship explanation by James Howat.