Why do recipes always specify that you use cold water? Yes, sometimes it might make a negligible difference in cooking time. I also realize that 1 tbsp. hot water contains slightly less water than 1 tbsp. cold water. But both hypotheses seem lame to me, at least when you’re cooking macaroni and cheese. Any culinary scientists out there?
Two reasons:
Cold water slows down chemical reactions, and hot water has a tendency to cook things. Dumping hot wait into your favorite Betty Crocker Cake-O-Rama Mix would cook the eggs before you mix it thoroughly, which makes the cake gross and lumpy.
In some more “challenging” recipes, the mixing can cause the ingredients to bind too quickly, so you use cold water to slow down the process.
Oops, meant “dumping hot water.” Brain fart.
I think the main reason is that hot water sits in the water heater tank for perhaps days, and may pick up funny tastes.