"I will not move my army without onions" declared General Ulysses S Grant in an advisory to the US federal government in 1864. He was immediately sent three train carriages loaded with onions, which the soldiers ate and used for their anaesthetic properties to treat gunpowder burns. Failure to send such an essential consignment might have ended in tears for the government, but the delivery would certainly have precipitated the odd bout of blubbering among the soldiers in any case.
Slicing onions breaks up cells that release a slew of chemicals, which quickly generate sulphenic acids. The resulting gas reacts with the water in the eye to form a weak strain of sulphuric acid, which is why you probably resemble a six-year-old whose birthday party has been cancelled whenever you make salsa. There are hundreds of ways to prevent a sobbing fit when you slice an onion, some being more effective than others. Many believe that a mouthful of chewing gum stops the gas from reaching the eyes, while others just stick their tongue out in the vain hope that their lolling licker will absorb the fumes before they travel further north. Rather than looking like a panting beast when you're cutting up onions, you may prefer to add water to the onion to inhibit the gas, or pop the peeled onion in the freezer for ten minutes prior to chopping. But many chefs prefer a swift slicing action and a very sharp knife that cuts - instead of crushes - the onion, as the simplest and most effective solution.
Of course, like politicians, some onions cause more trouble than others. Generally speaking, there are three types of onion: yellow, red and white. Yellow onions are the ones that will turn your visual sprinkler systems on, since they are very pungent. The tiny shallot is a prime example of a feisty, flavourful onion that's to be treated with respect. Red onions are milder, yet still pack a punch. They're great for slicing into rings and adding to a salad for colour and taste. The inoffensive white onion will cause you far less grief at the slicing stage, and will still endeavour to bring flavour and texture to salads, casseroles, curries - you name it.
Whatever your tolerance levels, it's a fact that the more pungent the onion, the more good it will do you. Shallots, for example, are rife with phenols (which provided General Grant's troops with their anaesthetic and antiseptic treatments). And Western Yellow onions contain the most flavonoids, which have antioxidant properties that can supposedly ward off stomach cancer. In fact, onions are believed to be effective at reducing cholesterol, treating colds, combating heart disease and reducing the risk of osteoporosis. What better to keep an army marching?