Why shouldn't you compost cooked food and meat?

Because a domestic compost heap cannot reliably reach the temperatures needed to handle them safely, and because they attract exactly the wildlife you do not want.

The problems:

Pests. Meat, fish, dairy and cooked food — particularly anything oily or containing fat — are highly attractive to rats, mice, foxes and flies. A heap containing them becomes a food source, and rats in particular will nest in the warm, sheltered interior. This is the single most practical reason and the one most people encounter.

Pathogens. Meat and cooked food can carry organisms that are destroyed only at sustained high temperatures. Commercial composting operates as a hot process, holding temperatures around 55–70°C for days, which kills pathogens and weed seeds. A typical garden heap is a cold process, running at ambient to modestly warm temperatures — it composts perfectly well, just slowly, and it does not sterilise.

Smell and anaerobic conditions. Fats and proteins break down slowly and produce strongly unpleasant odours. Oils also coat other material and exclude air, pushing the heap anaerobic — which smells worse and composts poorly.

Legal restrictions apply in some jurisdictions to composting animal by-products, particularly where livestock could access the material.

What to do instead:

Council food waste collection, where available, goes to industrial in-vessel composting or anaerobic digestion designed for exactly this.

A Bokashi bin ferments cooked food, meat and dairy anaerobically with inoculated bran. The output is pickled rather than composted, and is then buried or added to a heap where it breaks down quickly.

An enclosed hot composter or a wormery, though worms dislike meat and citrus.

A dedicated sealed digester sunk into the ground.

What is fine: raw fruit and vegetable scraps, eggshells, coffee grounds, tea leaves, and plenty of dry brown material to balance them.