A fork?

The Nitrobacteria and Nitrosomonas need air in the mixture to help break it down. It sets too compact and stale after the first heating process. Also azotobacteria and clostridium absorb nitrogen from the air.

Oh that sort of need DB!

Lol, Denise.

Actually, you don't need to turn it. Leave it alone and it will turn into perfectly good compost on its own, it just takes longer. We empty our bins once a year, throw the material that hasn't broken down sufficiently into an empty bin and use the rest.

I can be really boring on this subject, but here's a bit in layman's terms to be going on with - if you don't turn the heap, it usually doesn't get hot, so the only bacteria breaking anything down are anaerobes - turning it regularly means other bacteria (mentioned above by Docbob) are present, and these work faster, so, with regular turning and the right composition and moisture level, you can have an aerobic heap ready for use in 3-6 months - an anaerobic one can take up to two years.

Even if it's in winter, I still like to 'invert' the contents of my bin. This brings the 'bottom to the top', breaks up any compacted bits, and adds air to it.