Cooking advice gets transmitted with a confidence that has nothing to do with whether it is true. I collected the ones I had been given and tested the ones that were testable, which took a couple of years of paying attention.
Most were wrong. Two were right for reasons different from the ones given.
Searing seals in the juices
The most repeated claim in cooking and it has been thoroughly disproven for a long time.
A seared surface is not waterproof. Meat that has been seared loses moisture at broadly the same rate as meat that has not, and the experiments demonstrating this are old and unambiguous.
What searing does is create flavour through browning, which is an entirely sufficient reason to do it. The sealing explanation was a nineteenth century hypothesis that stuck around long after it was abandoned by the people who study it.
So: keep searing, discard the reason.
Salt makes water boil faster
It does the opposite, very slightly. Dissolved salt raises the boiling point.
The effect at cooking quantities is small enough to be irrelevant — a fraction of a degree — so in practice it neither helps nor hinders.
Salt the water because it seasons the food, which it genuinely does and which is the only reason worth having.
Alcohol cooks off completely
Widely believed and not accurate.
Studies measuring residual alcohol after cooking have found that substantial amounts remain, depending heavily on cooking time, temperature and whether the pot is covered. Brief cooking retains a lot; long simmering retains less; nothing tested reaches zero.
For most people this is irrelevant. For anybody avoiding alcohol for medical, religious or personal reasons, it matters, and they are frequently told confidently that it does not.
You must not wash mushrooms
The claim is that mushrooms absorb water and become soggy.
Testing this is easy and people have. Mushrooms absorb a very small amount of water in brief washing — a few percent of their weight — which is far less than the water they already contain and far less than they release during cooking.
Sogginess comes from crowding the pan, not from washing. Wash them, dry them roughly, and cook them in a pan that is big enough.
Adding oil to pasta water stops sticking
The oil floats on the surface and has almost no contact with the pasta. When you drain, most of it goes down the sink.
What little coats the pasta then prevents sauce from adhering, which is the opposite of what anybody wants.
Stirring in the first two minutes is what stops sticking, because that is when the surface starch is at its most adhesive.
Beans must never be salted before cooking
The claim is that salt toughens the skins and prevents softening.
Testing suggests the opposite. Beans soaked in salted water and cooked in salted water tend to soften more evenly and have skins that split less, because the salt affects the pectin in the skin.
The persistent belief may come from confusion with acid, which genuinely does slow softening. Tomatoes added early to a pot of beans will noticeably extend cooking time.
The two that were right
Let a roast rest before cutting it. This one holds up. Resting allows moisture that has been driven toward the centre to redistribute, and a rested piece of meat loses visibly less liquid when cut. The mechanism is not quite what people say — it is about temperature equalisation more than about muscle fibres relaxing — and the practical advice is correct.
Do not crowd the pan. Entirely correct, for exactly the reason given, and it is the single most consequential piece of kitchen advice on this list. Too much in a pan drops the temperature, water is released faster than it evaporates, and everything steams instead of browning.
Why the wrong ones survive
Something I have thought about since.
Most of these are unfalsifiable in normal cooking, because nobody runs a control. You sear the meat, it is good, the explanation goes untested.
They also tend to come with a mechanism that sounds plausible, and a plausible mechanism is very convincing to people who are not going to check.
And they are passed down by people we trust about cooking, which makes questioning them feel like questioning them, rather than questioning a claim.
The useful habit, which I have adopted slowly, is to separate what to do from why to do it. A lot of traditional practice is correct and the explanations attached are frequently later inventions.
The ones I could not test
For completeness, some claims are not testable in a domestic kitchen and I have left them alone.
Anything about how a particular pan material affects flavour, where the differences are small enough to be swamped by everything else.
Anything about resting dough for specific durations, where the variables are too numerous to isolate at home.
And most claims about what time of day something should be cooked or eaten, which are cultural rather than empirical and are not the sort of thing an experiment settles.
I have kept doing several of these anyway. Untested is not the same as wrong, and a habit that costs nothing is not worth fighting.