Bog butter, AKA butyrellite, is a waxy, buttery substance that is sometimes dug out of bogs in Ireland and Scotland. It is the result of a somewhat mysterious and ancient practice in which tallow or butter/milk was buried in wooden containers in bog peat.

Bog butter has been found buried in everything from dishes to barrels, baskets to leather or bladders -- anything that might approximate a watertight seal. The peat provides an anaerobic and acidic environment that preserves food well and inhibits bacterial growth, but it is unclear if this was a method of simple refrigeration or if it was a way of preserving through fermentation, à la the Middle Eastern smen butter.

Modern experiments in making a fermented butter in this fashion have been edible, but not entirely pleasant. Given that butter was a bit of a luxury, it is uncertain whether it would have been stored in this way in case of a famine -- it seems likely to be more useful for trade or immediate eating. It is possible that bog butter was an attempt to preserve and even strengthen butter for medicinal purposes -- for example, as the base for ointments -- which might explain why tallow was also preserved in the same way. Since butter was sometimes taken as tax, it is possible that it was stored -- or hidden -- until the taxman cometh.

The earliest examples of bog butter are thought to have been buried sometime circa 400-350 BC, and there is some evidence that the practice continued until at least 1850s-60s. Despite this, bog butter remains largely a mystery.

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