Q. “Bring a pan of water to the boil, generously salted, add the spaghetti
or…” seems to be a default setting for recipes for cooking pasta & most
vegetables. Is there a scientific reason for cooking pasta etc in salted
water? I haven’t done so for decades but wonder if I’m missing something?
A. Indeed, you are missing something when it comes to pasta. Italians believe, quite rightly in my view, that if you salt the pasta water correctly, you shouldn’t need to season it afterwards. Not only that, but according to the great Harold McGee ‘salt in the cooking water not only flavours the noodles, but also limits starch gelation and so reduces cooking losses and stickiness.’ So the equally magisterial Marcella Hazan suggests the following ratios: 1lt water per 100g dried pasta or 4lt per 450g dried pasta. And 1 ½ tbsp salt (22.5g) per 4 lt water.
With vegetables it is another matter. We cook vegetables to soften them, and so make them edible and easy to digest. It doesn’t matter which cooking method you use, you’re bound to loose some of their nutritional qualities, because heat causes chemical reactions in the vegetable. And don’t think you can get those lost nutritional bits and bobs back by adding their cooking liquor to the gravy or anything else because they simply dissolve into the surrounding water. Sadly, nature isn’t quite as straightforward and sensible as that.
Basically, the quicker you can cook a vegetable, the better, but it’s not quite as clear-cut as steaming good, boiling bad. For example, it may be better to cook potatoes below boiling point at 80-85C so that the outside and inside cook evenly, and you don’t suffer from exploding potato syndrome. Steaming is a good way of cooking green veg because they’re not bouncing around in the boiling water, leaching out flavour, colour and nutrients as they do so. On the other hand, you can only steam one layer of vegetables at a time if the steam is to surround, and so cook them evenly. Also, steaming takes a little longer than boiling because boiling water dissolves and extracts some pectin and calcium from the cell walls, while steaming doesn’t have that effect. The effectiveness of boiling can also depend on the hardness and the pH level of the water. Ideally, it should be soft and neutral or very slightly alkaline. A little salt (3%) also speeds up the softening process and reduces the level at which nutrients are leached out. Incidentally, perhaps the best way to keep in all those minerals and vitamins is by chopping them up small, and cooking them in very little water in a microwave. Whatever next?