Food preservation

Here's a small sample from Not Your Usual Science, which is now finished, but getting a last polish. That will take a while, as it ended up at 460,000 words. It will be out on Kindle in a month or two.

The illustrations are from a recent visit to Sri Lanka, where I saw fish being sun-dried.

Negombo beach, tuna.

Nobody ever sat down and thought “today, I will invent technology and change society”. It was more likely to be a matter of certain aspects of technology emerging, after which people used the new ideas, and only realised later that they had changed their society. Even more likely, they found a new way, used it, and changed their habits, which in turn changed society.

Before the development of agriculture, people had to live a nomadic life, moving after the food, following the seasons. Once they had ways of growing food near a permanent home, they could settle in one place, but then they needed ways to preserve and/or store food, to stop it going bad.

A closer view of the tuna

The process would have begun slowly, because even nomads knew how to smoke meat over a slow fire, or use sunlight to make beef jerky. Fish could also be dried or smoked. Before people knew about germs, salting was a good way to stop germs growing on meat.

Water can flow out of living cells and it can also flow back in through the cell membranes. High salt concentrations outside a cell stop water going back in, so any microbes in salted food soon dry up and die. When beef or other meat is dried, the salts in the meat are left behind, and once again, the salt levels stop bacteria and fungi from growing. (If you want to know what is going on here, the key word is osmosis, but right now, we are discussing history.)

Bees have used the drying method for millions of years, collecting nectar and fanning it to evaporate off most of the water, changing the nectar to honey. Spores and germs that fall into the honey simply cannot grow. When sugar cane is crushed, the juice is boiled and this concentrates the solution to stop any fungi or bacteria surviving in it.

All sorts of fish are dried.

By good luck, heating the cane juice also destroys a natural enzyme in the sugar cane which breaks the sucrose molecule down into simpler sugar molecules which are less useful, and the whole sugar industry depends on destroying this enzyme.

Islamic societies around the Mediterranean followed to a greater or lesser extent the teaching in the Quran that drinking alcohol was wrong, but even pious Muslims still liked cooling drinks. Highly concentrated fruit juice and sugar would keep forever, as nothing could live in it, but this cordial could be mixed with cool water to make a pleasant drink.

They are mainly carried inland and sold. Without fish, the
inland folk would have an iodine deficiency and goitre.
In a very real sense, the population depends on dried fish.

When the Egyptians preserved dead bodies, they used a similar method, but they replaced ordinary salt with natron, a mixture of sodium carbonate and bicarbonate which, as we have seen, was also used in glass making. The mummies would have tasted better with salt, but as nobody planned to eat them, natron was fine.

All the same, it would be reasonable to suspect that the Egyptians knew about salting meat before they made mummies, which would mean they must have started salting meat at least 4500 years ago.

Whatever method is used, preservation either sets out to kill the food-spoiling microbes, or to slow them down, making the food last longer. Warming up food makes a perfect environment for germs to multiply, and “food poisoning” often begins with warmed-up food being set aside and then heated again.

Geoffrey Chaucer was an English poet and scholar who died in 1400, as the Middle Ages came to an end, but he knew all about this danger. In his Canterbury Tales, Chaucer has a character accuse a cook of ignoring this risk. The Jack of Dover mentioned here was almost certainly a pie of some sort:

And many a Jakke of Dovere hastow soold,
That hath been twies hoot and twies coold.

 In more modern (but similar) language, this says:

And many a Jack of Dover hast thou sold,
That had been twice hot and twice cold.

Refrigeration is a good way of slowing down germs, but as Chaucer knew, more than 600 years ago, the cook’s habit of re-warming food made it potentially deadly. Unlike Chaucer, we realise that repeated warming of food can increase the number of bacteria to dangerous levels, but even without knowing about germs, Chaucer knew that reheated food was dangerous.

We can look at a food preservation method today and see the science which lies behind it, but each of the methods must have been originally discovered by chance, perhaps when an animal drowned in a brine pond, and was later found, free of rot.

Food left too long over a low fire may have been dried or smoked, wheat and barley stored in pots in hot dry places stayed dry and undamaged, and so on. Freezing of dead animals caught in a snowdrift may have preserved their meat, but looking into this actually killed one scientist, Francis Bacon, also known as Lord Verulam:

Mr Hobbs told me that the cause of his Lordship’s death was trying an Experiment … it came into my Lord’s thoughts, why flesh might not be preserved in snow, as in Salt. They … bought a Hen, and made the woman exenterate it, and then stuffed the body with Snow, and my Lord did help doe it himselfe. The snow so chilled him that he fell immediately ill … they put him into a good bed, warmed with a Panne, but it was a damp bed that had not been layn-in in about a yeare before, which gave him such a colde that in 2 or 3 dayes … he dyed of Suffocation.
— John Aubrey, discussing Francis Bacon (1561 – 1626), Aubrey’s Brief Lives, 179.

Whichever way the food was preserved, even without knowing anything about the spores, bacteria or fungi, humans stopped their food spoiling. The result was that people were able to live through bad seasons or times when there was no food to be had. They were also able to store food such as turnips or hay to keep animals alive, and dried foods were light enough to carry on long journeys.

Unfortunately, some preservation methods also destroyed any vitamins that might have been in the foods. Sailors and other travellers who tried to live on salt meat and ship’s biscuit (a very dry sort of bread) risked developing ‘disease’, as scurvy used to be called. On short voyages, the passengers and crew had enough vitamin reserves in their bodies to stay fairly healthy, but as voyages grew longer, people began to sicken, or even die, killed by the preserved food they thought was keeping them alive.

Pickling with a mixture of salt and vinegar can stop vegetables spoiling. Salt does not destroy vitamin C, the cure for scurvy. Salt meat has no vitamin C because the original meat had none, but pickled cabbage, sauerkraut, still has most of the vitamin C found in the original cabbage. Lime juice was boiled to a concentrated germ-resistant syrup. That usually kept some of its vitamin C, so long as the lime juice had not been boiled in copper pots. Copper surfaces are very good at destroying the vitamin.

Preserved foods allowed Europeans to discover the whole world and then dominate it. It was a mixed blessing, when you consider how they treated those they dominated!