A food waste digester will safely compost all kitchen food waste, cooked or uncooked, including plate scrapings, left over takeaway food, meat, fish, small bones, bread, dairy products, vegetable peelings and fruit.
The 3 most popular domestic food waste digesters available in the UK are the Green Cone, the Green Johanna and the Hotbin.
They are installed in the garden and look quite similar to normal compost bins. All use natural processes to break the food down without producing methane.
The Green Cone is a food waste digester which will process all the household food waste, cooked or uncooked, produced by an average family of four - about 4 to 7 kg per week.
This is a great low-maintenance system if you simply want to reduce the amount of rubbish that goes into your bin, or if you're fed up with having a smelly bin which is only emptied fortnightly.
It doesn't take garden waste, doesn't produce any compost, and rarely needs to be emptied. Just throw in your kitchen waste! That's it!
The Green Cone is 27.5" high, 23" diameter at the base and 11" at the top, consisting of an outer cone with lid, an inner cone, and a below-ground basket.
The basket and inner cone are made of 100% recycled polypropylene. The cone and lid are UV-stabilised high density polyethylene.
The Green Cone is heated by the sun so it must be sited in the sunniest part of the garden – it won't work in a cold, dark or damp position. It also should be somewhere that's easy to get to as you will be emptying your kitchen caddy into it every couple of days.
To install the Green Cone dig a hole about 30" (80 cm) diameter and 24" (60 cm) deep – deeper on poorly draining soil. The base of the hole should be covered with well-draining materials such as coarse gravel or small stones.
The cone goes into the hole which is then back-filled, making sure the rim of the cone is below soil level to stop any smells from escaping. (More detailed instructions are supplied with the unit)
The Green Cone works by heating the air inside to encourage bacterial growth, and by allowing earthworms to move freely in and out of the basket to break down and remove the waste.
The Cone's contents are reduced down to carbon dioxide, water and a very small amount of residue.
If properly fitted the unit won't smell or attract vermin.
For an average family of 4 the basket should only need emptying every 2-3 years.
A Green Cone is very easy to use. Simply open the lid, tip in the contents of the kitchen waste caddy, and close the lid. No layering or stirring is required. In cold weather it may need a little accelerator powder to be added with the waste.
The unit will take a small kitchen caddy of waste every 1 or 2 days in the spring and summer or every 2 or 3 days in the winter.
Waste that can be processed includes meat, fish, poultry, small bones, bread, cakes, dairy produce, plate scrapings and leftover takeaway food, fruit, vegetables including leaves and peelings, crushed eggshells, tea bags (check bags are not plastic) and coffee grinds. It will also process a small amount of dog poo.
In our view the Green Johanna is the best of all. It’s a very simple, easy to use closed hot composting system which will compost all kitchen food waste, including cooked food, meat and fish, and garden waste too. It will process the average food waste of a family of 5.
This is a Swedish designed composter which received a Gardeners' World Magazine Star Buy award in 2012.
It's made of recycled plastic, cone-shaped, with small holes in the base which allow air and earthworms through, but are too small for rats or mice to get into the bin.
The bin is 37.5" tall, 31.5" diameter at the base and 21" at the top, with a capacity of 330 litres.
Unlike the Green Cone or traditional compost bins, a Green Johanna must be positioned in the shade, out of direct sunlight, the shadier the better. If the temperature inside the bin gets too high it will kill the micro-organisms which break down the organic materials in the compost.
It must also sit directly onto the soil, not a hard surface or concrete slabs.
There is an optional insulated jacket which can be fitted in the winter to keep the composting process active when outside temperatures fall below 5 degrees C.
Adjustable vents help regulate temperature and moisture levels, controlled by turning the lid.
This system operates at its best with a mixture of 2 parts food waste to 1 part garden waste. The materials should be added loosely in thin layers, with each addition of food waste covered with a layer of preferably chopped or shredded garden waste.
A special stirring tool is supplied with the Green Johanna to mix the previous material each time new waste is added.
The compost is ready after 4 to 6 months and is easily removed through 2 doors at the base.
A Green Johanna will compost weeds, leaves, grass clippings, sawdust, wood shavings, shredded paper and cardboard, cooked food waste, bread, meat, fish and bones, dairy foods, crushed eggshells, coffee grounds, vegetable and fruit peelings.
The video below is a useful comparison of the Green Cone and the Green Johanna.
If you are prepared to put in a little more time and effort, this is the one for you. But, be warned - monitoring the temperature and adjusting the food supply can become a little obsessive!
The Hotbin is designed and made in the UK.
The standard *Hotbin Mark 2 is a highly insulated 200 litre capacity bin, measuring 1145mm x 550mm x 550mm. It was voted Best Compost Making Product 2018 by readers of Grow Your Own Magazine.
The new *Hotbin Mini is half the capacity at 100 litres and measures 1125mm x 450mm x 450mm. It was awarded the RHS Chelsea Product of the Year 2019.
The Hotbin is designed to operate at an internal temperature of 40 - 60°C. The makers say it will compost kitchen and garden waste 32 times faster than a traditional cold bin, producing finished compost in 90 days or mulching compost in 30 days.
It looks a bit like a tall wheelie bin and, at first glance, appears to be made of expanded polystyrene. However, it's actually made of a specialist highly insulating and durable plastic - expanded polypropylene (EPP) - often used for car bumpers and 100% recyclable.
There is a thermometer in the lid together with a ventilation valve to control the internal temperature, plus a long stem thermometer to check the temperature of the composting waste.
The Hotbin will take all cooked and uncooked kitchen scraps - plate scrapings, meat and fish leftovers, fruit and vegetable peelings - plus general garden waste including grass clippings. Provided high temperatures are maintained it will also safely compost pet waste (source).
To maintain a high temperature between 40-60°C the Hotbin needs at least a 5 litre caddy of kitchen or green garden waste to be added regularly twice a week. This is the average amount of waste for a medium household of 3 to 5 people with a small to medium sized garden. The Hotbin Mini will take the waste from an average 1-2 person household with or without a small garden.
If less waste is added the bin will still operate but at a lower temperature. The waste will take longer to break down and you will not be able to compost cooked wastes or animal waste as there will not be enough heat in the bin to destroy the pathogens in these types of waste.
Kitchen waste or grass clippings must be mixed with the correct amount of a bulking agent such as woodchip to maintain the airflow and add carbon to the mix. The manufacturers recommend about one part woodchip to 10 parts food waste – two handfuls for each 5 litre caddy of kitchen waste.
Shredded paper or cardboard is also recommended to control the moisture content - for every full container of waste about half the same container of shredded paper is added.
Many people absolutely love these bins and they have received various awards, but they do need more attention than a Green Cone or Green Johanna to ensure they have enough to eat in the right proportions with the right amount of air and moisture.
See Alys Fowler's article on the Hotbin in The Guardian here.
The video below has more details of how to operate a Hotbin.
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