What is a false boil?

In boiling, a false boil or bump roll is a phenomenon in which a liquid appears to be boiling vigorously but is actually not. It is caused by the formation of foam or bubbles on the surface of the liquid that rise and burst. This action gives the appearance of boiling, but the temperature of the liquid is not high enough for true boiling to occur. False boiling typically occurs when the liquid is heated too quickly, or when there are impurities present in the liquid that cause the formation of foam or bubbles.