When making homemade caramel, do you stir the sugar, or just let it sit while brushing down the sides of the pan with water?
I'm assuming you're making caramel using the wet method (sugar in water). What I do is begin my caramel in a pan with a lid. That essentially mimics brushing down the sides as water condenses on the underside of the lid and sides of the pan and drips down onto the sugar while it cooks. I keep the lid on and check every so often until the mixture reaches a rolling boil, at which point I remove the lid and pick up the pan to just swirl the mixture around inside every so often to help the caramel color more evenly. Stirring in the initial stages of cooking sugar with the wet method can cause it to crystallize, and there's really no need to stir since it's easy to make a great caramel without having to do so. However, when using the dry method of making caramel, the point is to cook sugar by itself over heat, in which case you do need to stir frequently for even cooking and to avoid burnt caramel.
You have to stir it when first combining the sugar & water, to fully hydrate the sugar crystals. Failing to do so can lead to crystallization.
Also, it's very possible to over think wet caramels. A little swirling of the pan is OK to get even colour and heat distribution, as long as you don't actually stir with a utensil. You want to avoid any condensation or contamination, which is what can cause the sugar to seize. Therefore make sure to fully cool before covering.
I feel that this is a case where multiple methods can be used to achieve the same result. I actually don't stir in the beginning since I first put the water in the pan THEN add the sugar by pouring it into the center of the pan onto the water, which keeps stray crystals from getting wet and clinging to the sides of the pan during stirring. When heated gently, the sugar dissolves slowly and hydrates fully while coming up to temperature without crystallizing. Perhaps I am one of few, but I have never had a problem with crystallization using a covered pan in the first stage of cooking, and, as it actually keeps water from reducing at first, it can prevent problems from accidentally cooking at too high a heat at which point the water can reduce more quickly than desired causing the sugar to burn. Since in many cases you would either be washing down the sides of the pan or keeping a lid on while the initial amount of water is still present, you are much less likely to have a problem than you would if you were adding water to the sugar after evaporation (at which point, the hygroscopic nature of sugar could cause it to crystallize). Condensation does, however, cause the crystallization of cooled confections and caramel which is often why the shelf life of such products is shorter in humid environments. I know that some people prefer to avoid washing down the sides, covering the pan, or micro-managing crystallization altogether, but this method is what I've found to be the best for me. I've also acidified my mixture at times with a few drops of lemon juice which acts (with heat) as a catalyst to convert the sucrose molecules in sugar to glucose and fructose, at which point it becomes an invert sugar and is less easily crystallized.
what sort of "contamination" are you referring to? I've always made my caramel with out a lid, without stirring or swirling and just brushed the sides with water. I've never really had an issue, but I also watched it like a hawk.