Three matters are forbidden to a nazir: tumah, head-shaving, and products of the grapevine. All products of the grapevine may be combined with one another, and he is not liable until he eats an olive’s bulk of grapes. [According to the] earlier mishnah: until he drinks a reviis of wine. R’ Akiva says: Even if he soaked his bread in wine, and there is in it enough to add up to an olive’s bulk —- he is liable.