Is it normal for hot mustard oil to foam strongly when ingredients are added, and why does it? I noticed that my mustard oil (of indian brands, as bought outside india, from specialty grocers carrying indian ingredients) tends to foam/bloom much more than other strongly heated oils when adding dried spices, gram flour and similar ingredients.

Is this an innate behaviour of this oil or a sign of an adulterated oil? If it is innate, what is the scientific reason behind this behaviour?
This is because all the Indian brands I know use the cold press method. In that process, some moisture is left in the oil that makes foam while heating. It's absolutely normal, and it's good that it has no chemicals. Hope this will help.