This week I’d like to write about canning.
No, no, no, this isn’t a column about corporal punishment in Singapore. “Canning,” not “caning,” as in, “Open up another can of beans, Ma, company’s coming up the walk.”
Canning is a form of food preservation, something humans have been interested in ever since some early hominid discovered the principle of the best-before date: a haunch of mastodon is best before it turns green.
Food spoils for a number of reasons. Topping the list are microorganisms. Bacteria and fungi feed on the same food we do and excrete noxious substances in the process. Enzymes, which are present in all raw food, are catalysts: they speed up chemical reactions, which in turn alter textures and flavors. Reaction with atmospheric oxygen causes fruits and vegetables to turn brown and oils to become rancid. Insects and rodents eat what they can get at.
No single method of food preservation protects equally well against all of these hazards. A lot depends on the climate. Canned food stored in Antarctica has remained edible for 50 years, but canned food stored in the Amazon rain forest wouldn’t.
The oldest methods of preserving food are drying, salting and smoking. Microorganisms require water; drying removes it. Salting accomplishes much the same thing; the salt binds with water molecules in the food, so there’s less water available for microorganism growth. Smoking both dehydrates foods and impregnates them with bactericidal chemicals such as formaldehyde and creosote. (Yum!)
More modern methods of food preservation include freezing, dehydration (a fancier and more effective form of drying), freeze-drying (dehydration using cold instead of heat), irradiation, and the one I want to talk about specifically, canning.
In 1795 the French offered a prize for the invention of a new method to keep food safe for military troops in the field. In response, Nicolas Appert, a chef in Paris, developed the canning process–which involved not only coming up with the idea, but inventing the necessary containers, in his case, glass bottles closed with cork and wire. At the same time he invented the process (he won the prize in 1810), the tin-coated metal can was patented in England. The two new inventions were obviously meant for each other, and so Appert’s process became known as canning.
Home canning really took off after 1858, when the American John Landis Mason invented a practical airtight glass jar-and-lid combination now called the mason jar: a jar sealed with a metal disk and rubber sealing ring, held tightly in place by a screw-on lid.
Whether canning is done at home or in a factory, the process is basically the same. First, you need something to can, usually high-quality fresh produce: an ear of corn, for example. The produce is washed, sorted and prepared for canning. In corn’s case, that process includes getting the kernels off the cob, since canning an entire ear of corn is problematic, to say the least.
At home, people scrape corn off the cob using a sharp knife. In factories, they do much the same thing, only there are six knives, they’re very carefully shaped, and they rotate around the ear at high speed. Ears of corn are fed one at a time into this machine, tip first. The knives can be adjusted to slice off the kernels at any level you please, and they’re designed to automatically allow for the tapering shape of the ear–important, because otherwise you’d end up with some kernels not sliced off at all and others sliced off with a large chunk of the cob still attached.
There are completely automated machines for doing this, but in many factories–such as the one I contacted in Minnesota to find all this stuff out–the machines are fed by hand, an operator individually placing the ears of corn onto the conveyor taking them into the slicing machine. A skilled operator, I’m told, can feed 6,000 ears of corn an hour into the machine. (And you thought YOUR job was boring…)
Once properly prepared, the produce is placed in the canning container (glass or metal). Water or syrup is sometimes added, though the container is never completely filled. The remaining air is driven out by heating the filled containers for a few minutes (which causes the contents to expand until there’s no room for any air), then the container is sealed and the sterilization process begins.
How hot the can has to be heated and for how long depends on the food. Many fruits have lots of acid in them; they can be sterilized by putting the cans in boiling water for less than half an hour. Meats, fish, poultry and vegetables, however, don’t have much acid and have to be heated at 115 degrees Celsius for a longer period of time. You can’t heat water past its boiling point of 100 degrees at ordinary air pressures, so these foods require a pressure-canner.
Improperly canned foods–foods not boiled long enough, or at high enough temperature–can literally kill you, because of an organism called Clostridium botulinum, which produces a toxin that causes a sometimes fatal form of food poisoning called botulism.
The traditional “tin can” is actually made of sheet steel; it’s only coated with tin, which keeps the steel from corroding. The sheet steel is rolled into the shape of a can, then seamed; the top and bottom are die-cut and attached separately. Since the 1960s, aluminum cans have been increasingly used for canned liquids; the cylindrical part of aluminum cans is seamless, with only the top added separately. Of course, as already noted, glass containers are also used as “cans;” there are also plastic cans and even “cans” that are flexible plastic pouches.
The biggest problem with canned food is that the heat treatment to prevent spoiling also causes foods to lose juices, texture, flavor and nutrients, which, when you think about it, are all the most important elements of food. This is why I like fresh or frozen peas, but I hate canned peas.
On the other hand, the only time I ever ate haggis, it came out of a can, so maybe I should give canned peas another try.
After all, if you can eat canned haggis, you ought to be able to eat anything.
