I don't watch it very often, but the portions of food are hardly big, are they?
Anyway, the judges would only need to sample each dish, rather than eat the whole lot. I would think the plates are cleared of food so that it looks good for the sake of the programme. I dare say the production crew finish off what is left over.
There were a few dishes last night that I expect the judges only had a very small amount of - one looked absolutely disgusting!
Do Greg or John stand outside the dining room door with the third plate for the judges? And why do they have to sit in a brick dungeon for their comments afterwards? They used to be interviewed on a sofa in previous series.