Dear friends, let's walk through the frying pans one more time. Rather, on the question of why, even with high-quality non-stick pans, products begin to stick (for someone - it happens earlier, for someone - later), and this trouble begins from the center pans?
Well, why the food starts to stick is understandable.
There is damage to the non-stick coating, and here it is - the result.
Damage to the non-stick coating even in good and high-quality pans, which are looked after according to all the rules - the pieces of iron are not scrape, do not wash with suspicious liquids, do not put hot under cold water, most often occurs during cooking food.
At the very moment when we pour oil into a hot frying pan.
Pouring oil into a frying pan that is already hot is a habit for many. I don't know why it appears, but with a non-stick coating, such tricks end up badly: temperature difference (hot frying pan - cool oil) affects it no better, this is the difference when a hot frying pan is pushed under a cold water.
But why does the middle suffer more?
It's simple. The middle is not the one that suffers more, it is just that during cooking or warming up, the middle gets less oil. Even when the layer of oil is so thin that it is very difficult to see it, the problem is still present.
I'm not kidding, I was surprised myself.
To be honest, I, like many others, thought that when the butter "scatters" to the edges of the pan, the curved bottom is to blame. Or the bottom that deforms during heating. However, the question - why such a phenomenon is observed even on thick-walled cast irons, in which the bottom cannot bend by default, still surfaced periodically.
And then I came across an explanation. Thermocapillary convection is to blame.
A whole study is devoted to her - "On formation of dry spots in heated liquid films", but, to be honest, clever words will say little to a person who took a physics course at school and has since then happily forgotten it.
Having made my way through the jungle of terms, I realized that when heated, the oil moves from the center of the oil slick to the edges, and thus forms what the author of the study (Fedorchenko) calls a “dry spot”. This is due to the surface tension, which, as I understand it, is higher at the edges than in the middle, and increases during heating.
If someone is interested in the mechanism of this phenomenon. which occurs during heating, then you can read for yourself, delve deeper. Well, as for the usual kitchen practices, it is enough to remember - in order to avoid oil escaping from the middle of the pan, it is necessary - completely cover the entire bottom with oil, do not overheat the pan and stir the food as often as possible.
Although I would, in the first place, put the rule "do not overheat", because many times I observed how even a sufficient amount of oil scattered to the edges, leaving the middle of the pan "bare". By the way, butter is more prone to such shoots than vegetable oil - I think you also noticed that a piece butter, melted for frying, very quickly begins to form separate "lakes", even if it melted butter.