Ugh...been through that only recently.
The junior football club chest freezer had been turned off by some bright spark at the end of last season and left closed. One of the other Mums and I were the bunnies who opened it
.
Gag reflex on overload - we managed to clear it out with passing out and then I asked Mike to bring the high pressure water cleaner down. Took the freezer outside; turned it on its side and hit the thing inside. Then I doused it oil of cloves mixed with water to kill off any of the mould spores after we gave it a good scrub.
Worked like a charm
.