If one eats very slowly, this is not considered eating at all. Thus, if he ate half an olive volume of a prohibited substance, and then another half, but took longer than a certain time period, he is not liable. How slow is slow?
Rabbi Meir says that we estimate how long it would take a person to eat the food if it had be crumbled into pieces as small as parched grain, and then eaten one by one. However, the Sages say that this time is measured by how long it would take a person to eat half a loaf of bread, four egg-volumes, and some say, three egg-volumes. The bread for measurement is made of wheat, which is eaten faster than barley, and in practice this time limit is between three to nine minutes. There is also an opinion that one can eat as slow as he wants, as long as he does not pause for the time it takes a normal person to eat half a loaf.
Consequently, if a Kohen drank a quarter of a “log” of wine (about 30 milliliters), during the time that it takes to eat a half a loaf of bread, he is forbidden to enter the Temple to perform service. After the Torah prohibits Kohanim from serving in the Temple while drunk, it continues to say that he needs to “Distinguish between the sacred and profaned, permitted and forbidden, and teach the sons of Israel.” By extension, one is not a allowed to render decisions on the matter of law while drunk. However, one is allowed to teach the Talmud.
Art: Hendrick Terbrugghen - The Merry Drinker