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HOT & COLD COMPOSTING

Benefits of hot composting over cold composting

Hot (40-65°C) Cold (0-40°C)
The right hot composting system will work all year round – which is relevant when composting food waste.
Cold heaps 'stop' in winter (-5 to +5°c). Anything added piles up until spring when the sunshine warms up the heap.
Hot Composting can take a wider variety of food waste types without causing issues.
70% all household food waste is not added to 'cold' compost bins as it is likely to cause issues with odour, rats and flies.
Hot composting kills weed seeds faster. The higher the temperature the more seeds are destroyed.
Many seeds will survive in 'cold' composting heaps.
Hot composting kills pathogens and unwelcome bacteria. Which and how many is a function of both time and temperature. 60C for 1 hour equals good sanitisation.
You need to leave cold compost a long time (12-18 months) to achieve the same level of sanitisation and bacteria to die off.
Hot composting is 32x faster than cold composting.
An ‘outdoor’ heap averages the same temperature as ambient air temp - i.e. 10°c. At 10°c the heap it is 32 times slower than at 60°C. If a soft waste like grass takes 6 months in a cold hep it will take about 2 days to reach the same state in hot heap. In general; cold = 12-24 months and hot = 1-3 months.
A hot heap rarely produces putrid odours. Hot heaps transfer water away from the heap as steam (as long as the waste has free air space which is normally provided by bulking agent).
In a cold heap, water is not evaporated; it has to drain to the ground. This happens slowly and poorly in compost, so it gets water logged and turns anaerobic and putrid. The main solution is not to add 'wet' food waste to cold heaps - most of our diet is foods with 80% water.
A hot bin will kill fly eggs & larvae - so no swarms of flies or maggots in a hot compost bin. It's too hot at the top for ants, rats, and most things you don’t like to see in a heap.
Flies will lay eggs and larvae (e.g. maggots) will be present in a cold heap, and often swarms of flies can come out when lid open.
Table excludes Vermicompost/Worms/Bokashi/AD, etc.

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