Now this is an interesting question, normally a plasterer working in brewery would be suffering a sore tummy (and head) from too much beer sampling! Plasterers & painters are known in the trades for their love of the suds. Stale beer was actually added to lime plaster as a "sizing" agent - this would be similar to adding gum arabic, it acts like a glue, helping it stick to walls and also forming a "skin" on the surface to make sure the gypsum is properly hydrated.

Another possible purpose to tasting the plaster is that sugar may have been added to the lime. For some reason sugar causes the lime to accept up 14 times more water - at the price of substantially weakening it at this high level. This would not be an issue with me and my home made, high calcite lime putty, but if you were ordering the "white gold" putty from Europe, you may want to check if it has been sugared/extended by tasting, but I doubt that any company would risk its reputation with this trick.