Lime power for cooking - medieval pots to 21st century cans

Quicklime fireless cooking, slaking lime with water for heat without fire

I was intrigued to discover a medieval version of today's self-heating cans of soup, beans, and coffee. In a Welsh museum is an Anglo-Norman double pot, a smaller cooking pot inside a bigger one, designed for cooking without any need for lighting a fire. In the space between the two pots you could set off a chemical reaction by mixing chunks of quicklime (photo right) with water. It created heat to cook the food inside the sealed inner pot.

Quicklime, also called lime or unslaked lime, is what's inside many of today's self-heating cans too. (More explanation at bottom of page.)

A recipe from 13th century England explains how to cook with a pair of pots and no fire. It really was cooking, not just heating up pre-cooked food and drink:

To cook meat without fire....

Take a small earthenware pot with earthenware lid of the right size. Then take another pot, also earthenware, also with a suitable lid that fits well. This should be five fingers deeper than the first, and three fingers bigger round. Then take pork and chicken, cut them into nice pieces, get good spices and put them in, and some salt. Take the little pot with the meat in and put it inside the big pot. Set it upright, cover it with the lid and seal with damp, sticky soil, so nothing can come out. Then take lime that has not been slaked [quicklime], put it in the big pot full of water, but take care that no water gets into the small pot. Leave it alone for as long as it takes to go five to seven leagues. Then open your pots, and you will find your meat well and truly cooked.

The original late 13th century recipe in French (A quire char saunz fu/A cuire chair sans feu) is in Hieatt and Jones' Two Anglo-Norman Culinary Collections

So who cooked this way? Was lime cooking for medieval outdoorsmen like the modern explorers, soldiers, and campers who carry survival rations in self-heating food packs? Is the "five to seven leagues" a clue that the recipe was for people who would walk fifteen to twenty miles while their dinner was cooking and had no time to sit tending a fire? How did the meat go on cooking once the lime and water reaction died down? Was the pot insulated with grass or earth?

Cooking an egg in lime and water doesn't need a fancy double pot, since the shell keeps the food and chemicals separate. One method is described in a popular French cookery book from the 1650s (see left-hand column), but the idea is much older. An early description of an egg cooked in a potful of water and lime seems to have come from the 10th century Persian scholar al-Razi, once known in Europe as Rasis. He treated it more like a magic trick than kitchen cookery.

Quicklime cooking took on a scientific tone in an early Victorian demo at the London Gallery of Practical Science. Here the "chemical lecturer" had apparatus for cooking a steak. The meat, which was cut up for the audience to taste, looked like boiled beef but had the "richness of a broiled rump steak" according to the Oxford Herald in 1836.

The most novel matter was a lecture by Mr. [William] Maugham, on an apparatus for cooking without fire. The experiment was shewn with a tin box, in the centre of which was a drawer, where beefsteaks and eggs were deposited. In the compartments, above and below, lime was placed, and slaked with water. The usual process took place, heat was disengaged, and the victuals were perfectly dressed, without receiving any peculiar flavour or taste from the means employed. ... The operation took about half an hour.

Literary Gazette, January 1835

Twenty years later in the USA, a "vapor stove" for cooking a full meal plus coffee (see the handy faucet!) with lime heat only was patented by W.W. Albro of Binghamton, Broome County, NY.

Coffee or tea is made in the space between the two vessels A C. Meat and vegetables are placed within the dish or vessel D, which may be provided with partitions to separate the different articles. A requisite quantity of quicklime is placed within the vessel C and the cover H is placed over the dish or vessel D. A requisite quantity of water is then poured [in and] falls through the perforated tube G in a shower upon the quicklime....

From then on there were plenty more attempts to harness the power of slaking lime with water to cook food away from home and hearth. This generally seems to have been an experiment, not part of ordinary life, despite optimistic remarks in patents about the convenience of being able to cook away from a kitchen or campfire. Self-heating cans for ready-made soup etc., which came on the scene around 1900, were useful for special situations like war and travel by air balloon. The most recent cans have a simple push-button to trigger the heat-creating reaction. Other chemicals as well as lime have been tried for self-heating food and drink.

With all the disposable packaging as well as the energy used to make quicklime, the cans are nothing like a green new way of cooking, even though they use no firewood and no electricity. But if you could make a safe low-tech lime stove, and use solar energy to "recharge" the slaked lime, turning it back into quicklime.... Yes, some people are working on a "rechargeable solar stove". A long way from a medieval earthenware double-wall cooking pot found on the English-Welsh border?

Quicklime has been known for thousands of years. It is made by heating limestone to high temperatures in a lime kiln. Slaking it, or mixing it with water, produces heat. The slaked lime is a traditional ingredient in mortar, plaster, and whitewash, and has many other uses.

Don't try heating food with lime if you're not sure how to do it safely. Handling lime is dangerous unless you are experienced with such chemicals. Skin contact or inhalation can cause severe reactions.

10 Aug 2010





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