What is the purpose of scalding milk for yeast rolls?

Scalding milk used in bread making was done because historically it was necessary to kill some of the bacteria present in milk before introducing the desired yeast, because the milk is then kept warm to encourage the growth of the yeast, and any undesirable micro-organisms would also grow in these conditions.

Modern pasteurized, sealed and refrigerated milk is less likely to require this treatment.

Scaling involves heating the milk until it is about to start boiling, then removing it from the heat.