Some food is untaxed. For example, cakes are untaxed but biscuits are taxed (or maybe it's the other way round). There was a court case to decide whether Jaffa Cakes were cakes or biscuits for the purposes of VAT: the court ultimately applied the principle that cakes were soft when fresh but hard when stale, while biscuits started off hard and then went soft; hence Jaffa Cakes were officially cakes.