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'''Coolship''' (the Anglicized version of the Dutch/Flemish ''koelschip'') is a broad, open-top, flat vessel in which wort cools. The large surface area in relation to volume allows for relatively efficient cooling. It is also an integral step in the process of making Belgian lambic and other [[Spontaneous_Fermentation|spontaneously fermented beers]]. Historically, coolships were constructed of wood, but later were lined with iron or copper for better thermal conductivity. Most modern constructed coolships are made from stainless steel, although copper coolships are still used in many Belgian lambic breweries as well as a few breweries outside of Belgium. Pre-dating the specific application of coolships by Belgian lambic brewers for inoculation during cooling, some German and English brewers also still use copper coolships (''kühlschiff'' in German and "cooler" in Great Britain) as chillers to partially cool wort to 55-75°C (131-167°F) before either chilling the wort in a closed system or transferring the warm wort to a fermenter to cool and finally pitch yeast, a process which was once common throughout Europe <ref>[http://craftybeergirls.com/2018/03/18/coolship-field-trip/ Lauren Lerch. "Coolship Field Trip". Crafty Beer Girls blog. Retrieved 03/18/2018.]</ref><ref>[http://www.uerige.de/brauerei-brauprozess.html "Malz – aus Gerste und Weizen ". Zum Uerige website. Retrieved 03/18/2018.]</ref><ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2814130411948488/ Various members of MTF. Milk The Funk thread on the use of coolships in historical German brewing. 07/28/2019.]</ref><ref>[http://zythophile.co.uk/2019/10/18/do-you-gyle-your-ale-after-it-leaves-the-cooler-and-finishes-fermenting-in-the-vat-or-krausen-your-beer-post-coolship-when-its-run-out-of-the-foeder Martyn Cornell. Zythophile website. 10/18/2019. retrieved 10/18/2019.]</ref>. Saison breweries used coolships during the 1800's in a similar fashion to German brewers to cool the wort before pitching yeast <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2275507945810740/?comment_tracking=%7B%22tn%22%3A%22R%2317%22%7D Georges Lacambre. Dec, 1851. Translated by Lucas Blasty on Milk The Funk Facebook group.]</ref>.
Contemporary usage also includes using a coolship as an open fermentor for the production of non-sour beer. For example, [https://web.archive.org/web/20220126000613/https://www.anchorbrewing.com/blog/brewing-insights-open-fermentation/ Anchor Brewing Co] ferments fermented beer openly, but because the wort is pre-chilled before entering the vessel, Anchor Brewing no longer refers to these as "coolships" but as "open fermenters" <ref>[https://web.archive.org/web/20230326181248/https://www.anchorbrewing.com/blog/anchor-terminology-coolship/ "Anchor Terminology: Coolship". Anchor Steam website. 04/12/2012. Retrieved 09/10/2018.]</ref>. Contemporary experimental usage of coolships includes allowing wort to cool and become inoculated with microbes from the environment, as well as adding cultured yeast at some point in the process, and optionally using the coolship as an open fermenter to conduct the primary fermentation in rather than conducting the primary fermenation in barrels like in Belgian lambic brewing. This is not considered to be full "spontaneous fermentation" since yeast and/or lactic acid bacteria are added to produce a more controlled fermentation, but the resulting beer might benefit from or be otherwise altered by the wild microbes or the effects of the lack of head pressure/exposure to oxygen caused by cooling (and optionally fermenting) the wort in a coolship <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2987548407940020/ Brandon Jones of Yazoo Brewing Co. Milk The Funk Facebook group thread on using a coolship and pitching Bootleg Biology yeast. 10/18/2019.]</ref>. A less common practice that has been gaining some traction in the US is using a portable coolship. These coolships are designed to be transported, often in the back of pickup trucks. The coolship should have a baffle that prevents the dangerously hot wort from spilling out of the coolship. The coolship can then be transported anywhere to inoculate the wort. See [http://allaboutbeer.com/article/portable-coolships/ this All About Beer Magazine article].
This article will focus on the use of a coolship to initiate spontaneous fermentation and will not significantly address the use of coolships to partially cool wort as in the German/English/saison methods of chilling wort or to conduct open fermentation.