TOP 4 Compost Bins? Grow Your own List HOTBIN
HOTBIN composter is listed in the top four composting bins in this weeks Grow Your Own Magazine.
You might want to take a look at out post on tumblers plus our post comparing HOT v COLD composting along with our HOTBIN reviews.
Tumbler versus HOTBIN
Tumbler compost bin versus HOTBIN with no turning
If you have landed on this page, you are probably trying to decide whether to buy a tumbler compost bin or the HOTBIN. We offer you a quick ‘expert’ recommendation and a more detailed list of items so you can evaluate the type of compost bin for yourself. Alternatively jump to over and read what HOTBIN customers say
Our expert recommendation: As soon as you set a goal to compost all food waste (including meat, leftovers, bread, pasta, etc), and you want to compost all year round (through winter), with no vermin, flies or odour, then you need to opt for a specialist ‘hot composting bin’. Many tumblers are not capable of hot composting. If you hot compost and use a bulking agent there is no need to turn your compost.
Decide for yourself (list of things you should review):
To establish if a product is “better” you need to take a step back and ask – ‘What am I trying to achieve?’
There are two sets of features to look at. The first group looks at whether you want to hot or cold compost, and the second group look at how easy the compost bin is to use.
Group 1 – Hot or cold composting?
Do you want to:
- Compost ALL food waste from a typical domestic home
- Compost all year round (i.e. through winter)
- Compost faster typically less than three months
- Compost difficult garden wastes (e.g. weed seeds, couch grass, etc.)
- Compost without rats, flies or odour
- Compost without turning (fork over the heap)
Vendors will try and persuade you their bin will do ‘a lot’ and you can ‘control things’. To a degree this is true – but there is a huge performance gap between a bin designed to hot compost and a tumbler that holds waste while it cold composts.
- Feed it the right mix of chopped up waste
- Retain heat – ie insulate it by using specialist insulating materials
- Aerate – harness the science of buoyant airflow to get air to each bacterium at microscopic level
- Control water – remove excess water from the mix
- Enclose the waste, remove odours and control vermin and flies
The items are connected – get all five right and it is a virtuous circle, get one wrong and it can quickly form a vicious circle, spiralling downwards out of control.
Feed it: Some materials compost faster than others. Feeding chopped up, ‘easy to digest’ waste allows fast digest and hence fast heat release.
Retain heat through Insulation:
All things compost faster as a function of temperature (read about the Q10 equation here)
. No compost heap will compost faster unless
it retains heat. Plastics are very poor heat insulators – do not get fooled by names like ‘thermo’ and a few extra mm of plastic. You need a top quality, waterproof insulated material/ Just like your loft insulation ask for U or R value rating! Most tumblers have no insulation of any significance so they do not retain heat. The HOTBIN is designed to control both conductive heat loss (via insulated walls) and convective heat loss (hot air flow). If your goal is to hot compost; walk away from non-insulated bins. If you goal is to compost typical amounts (2-5Kgs) of food waste through winter, check the insulation works – look for user endorsements offering time & temperature graphs using on known amounts of waste (Kgs/week). We are NOT aware of any insulated tumbler guaranteeing winter hot composting of 2-5Kgs per week.
Aerate the waste:
You can hot compost without turning! The science (ref in T Huag, Compost Engineering) states air introduced via turning will last only a short time. If you have twiggy/woody material that maintains ‘free air space’ structure and a temperature gradient, it will aerate via buoyancy air flow. To learn more about the theory of “no turning” visit our buoyancy airflow and free air space faq
Plus you need to take into account spinning or turning a compost tumbler is not always easy.
100 litres = 50 Kgs, 200 = 100 Kgs.
Even with levers this can be hard and it places huge stresses on plastic and metal joints.
Control moisture: This is critical to the composting process. Kitchen scraps are wet, as is grass clippings need to be balanced with dry materials. Some tumbler models have drain holes in the drum, and also a collection chamber in the base to receive the “compost tea”.
Wet waste: Wet waste tends to rise and then slumps to bottom – it churns into a solid sludge- the last thing you need! Wet waste is the norm when composting all food waste. This is really easy to handle in the HOTBIN – you just add shredded paper and bulking agent to balance the system.
N.B. Leachate: most of the excess water is driven off as steam in hot composting. Some excess will drain down. Look for a bin/tumbler that has some form of leachate collection
Control Odour: All composting produces odour. Aerobic composting avoids anaerobe pungent putrid odour – but it has a cabbage odour. You need to filter odour and reduce the any possible chance of attracting flies and vermin. Check if your tumbler has any odour filter mechanism – the HOTBIN does!
Pest control: Do not get sucked in by statements like “compost tumblers are 100% pest proof since they are fully sealed”. We believe no domestic compost bin is rat proof. Rat experts will tell you they will eat through all plastics (be it 3, 15mm PE or 50 mm EPP as in the HOTBIN) if there is any gap. Understand vermin – what attracts them (odour, warm and quite nesting sites), then look for design that makes the bin highly rat resistant. If you bins has ANY open holes of 0.5cm or larger and odour you will have problems sooner or later. Always look for off the ground, and look for a filter that removes residual odour to a very low non-nuisance level.
Group 2 – Usability factors
What are the key items that make it easy to use;
- Loading and unloading
Assembly: Bit of a preference – we suggest you look for bins that come ready assembled or at least require very little self assembly. HOTBIN requires none.
Loading and unloading: Small loading and unloading hatches panels are fiddle and difficult to use – it is a big issue for some composter. Some tumblers are good – others are hopeless. The HOTBIN is OK.
Batch or continuous: You can fill the HOTBIN to the top and leave a batch to mature (batch) or more commonly, you keep filling at the top and take out the compost from the bottom without stopping (continuous). With most tumblers there is the issue of when to stop adding new materials so that the whole composter can “finish” and the compost can be removed. Dual chambers are better than single so you can swap compartments, otherwise you may be looking at two bins. (This is a bigger issue if your goal is compost food waste over winter as you cannot stop for 2 months.
Durability: Choose carefully! Tumblers tend to be more heavily constructed since they need to be strong enough to hold the full weight of the composting materials. This does not always work – many fail at the joints and stands. Inspect the supporting legs and the central axis connection – they should be built to last years of use (Check for customer’s reviews after years of use!). The HOTBIN has no moving parts – and only a door to take on and off.
Size & Capacity: Avoid thinking bigger is better. Hot composting is typically 10-30 times faster – so you need vastly less capacity. When hot composting, match the size to the amount of waste – it is harder to get a big tumbler hot with a small amount of waste – the laws of physics do not support small amounts of waste getting or staying hot in large empty bins!
Price or rather value for money:
- The HOTBIN = £120-150
- Non-insulated tumblers = £70-500
- Insulated tumblers = £170-£450
HOTBIN composting supply a compost bin. If you are wondering how and why we are open about offering the secrets of buying the right bin – well its straight forward – our product is excellent, the customer’s reviews say it is excellent, we have used robust composting science and engineering for the design and operation. We have confidence you will choose the right product.
Jump back to HOTBIN products page. Jump back to your shopping cart
Grass composting in the HOTBIN
How to compost grass in the HOTBIN composter. What can you expect when you add grass into the HOTBIN
As we explained in our previous grass post there are advantages to adding cardboard (or shredded paper) plus bulking agent (wood chip) to the HOTBIN to help you compost grass most successfully; it helps calm the ammonia smell and creates extra structure.
Here’s what happens to grass in your HOTBIN through a series of pictures.
Grass added to the HOTBIN
One hour later …
24 hours later…see how it has shrunk already!
48 hours later…
4 days later…this picture speaks for itself
7 days later…It’s almost gone and is steaming away!
Our control experiment!
We put some grass in a bag outside with no insulation… the temperature never gets above 30C
After 24 hours…
After 48 hours…We added some insulation on the top to see if this helps?
After 4 days…The insulation hasn’t made a difference!
After 7 days…there is still no real drop in volume
How to compost grass lawn mowing
To get fast superb results when composting grass lawn mowings in the HOTBIN:
Add 40 parts grass with 20 parts shredded paper and 1 part wood chip (bulking agent)
Typically this is a medium sized lawn mower collection box (40 litres) with a full carrier bag of shredded paper (20 litres) and 4 hands full (one 2-litre measuring jug) of bulking agent.
If you want to view a photographic sequence of grass compost stages, you can jump to our post on steps / stages of grass composting.
Below we explain why this recipe works, why just adding large amounts of grass can be problematic and offer 6 different options for handling large volumes of grass cuttings
The problem often seen when composting grass is you end up with a black slimy layer that stops the compost heap working.
In a HOTBIN you should get brown mulch in 7 days
Grass is one of the quickest materials to compost. In the HOTBIN you can typically convert grass to mulch within 7 days. Grass is so quick to heat up to 60-70C, the HOTBIN team recommend it to help accelerate and increase temperature quickly.
BUT! You can end up with a black anaerobic slime
In traditional compost heaps, it is one of the most troublesome materials to compost. Grass often heats up for 2 days and produces a very distinctive whiff (ammonia/urine). After 2-days it then ‘collapses’ into a cold, wet, slimy black mass that smells horrible (anaerobic mush).
Funnily enough we don’t have a picture of this as if you do it correctly in a HOTBIN it shouldn’t happen!
Composting grass successfully requires a little bit of extra composting knowledge but the real secret is matching the amount of grass you generate with the time and effort you have available.
Why does grass turn into a slimy putrid mess?
The ‘black slime’ is due to anaerobic conditions, i.e. excess water and too little airflow. Grass (lawn mowing) has a high water content (>80%) and no lignin (i.e. no woody stalk). As grass starts to decompose, the plants cells break down and become soft; water is released. The grass collapses and forms a thick impervious layer and airflow decreases. This in turn means the water is trapped, the process slows and a vicious circle is created where water is not removed, all oxygen stops flowing and aerobic bacteria cease to release heat. The heap cools and anaerobic bacteria take over releasing obnoxious odour and resulting in a ‘black slime’.
The golden rules for successfully composting grass are:
- Remove excess water
- Keep the grass aerated
- Balance the mix to avoid ammonia odour
So how do we get rid of excess water, keep the waste aerated and avoid both ammonia and or anaerobic odour?
- To remove excess water
You need lots of heat, i.e. you need to be ‘HOT composting’
- To keep the grass aerated (i.e. get air/oxygen into the grass layer)
You need buoyant airflow which requires a temperature gradient and a structure with spaces and gaps so the air can flow up.
Unless you have the means to force airflow (e.g. a pump / blower), or you can constantly turn/tumble (yes we mean constantly), then you are reliant on “buoyant airflow via the chimney principle” – and this requires the grass to maintain a structure with small air spaces (ie not a thick wet slimy mass!).
To get a structure that stops grass collapsing into a slimy heap, you need to add what we refer to as a bulking agent (typically this is wood chip). The bits of wood chip act like ‘stacking blocks’ and the air flows around them. Simple but essential!
- To avoid ammonia odour
To prevent excess ammonia, you need to be adding a fast/easy to digest carbon material like shredded office paper or chopped up corrugated cardboard.
The odour is caused because grass has an excess of nitrogen which the bacteria are unable to use as fast as it is released. So it forms ammonia gas and evaporates away. You are most likely to notice this when composting and/or turning large quantities of 1-2 day old grass lawn mowing. After 3 days things slow down and the nitrogen is no longer in excess. Turning grass heaps does not prevent the odour – it enables the trapped gas to escape ‘all in one go’. (If you have done this job, you may well come back inside the house and realise your clothes smell of ammonia!).
The HOTBIN does have an odour filter in the lid that does remove ammonia odour. But, when you add a whole box of grass in one go without anything else, the filter gets temporarily overload for 2-3 days. To prevent the odour during the initial 2-3 days you need to balance the carbon/nitrogen ratio.
You achieve this by adding a dry high carbon waste. The key here is to add ‘easy to digest carbon’ such as corrugated cardboard or paper shredding. Woody items like sawdust, shavings, wood chips are high carbon – but they are not easy to digest, so will not balance the C/N during the critical 2-days of intense activity. Here is the challenge – you need a lot of dry carbon! A 40L grass box (a typical mower box), needs 20L of paper – that’s a whole carrier bag full. It also needs to be mixed with the grass. Not everyone wants to do this, especially after cutting the grass. Below we outline a few options about different methods you might want to follow.
Large amounts of grass waste need extra steps to compost quickly, without ammonia and without turning putrid. Is the extra effort worth it? We think so! Each year fertilising grass lawns consumes considerable inorganic fertiliser – adding the nutrients back via compost is environmentally better.
Below are six options/choices for composting grass. Often you can ‘mix ‘n’ match’ routines at different seasons and times of the year to cater for the varying grass volumes.
1) Small to medium lawns – add grass into your HOTBIN each week
The HOTBINn will easily compost grass from a small-medium lawn (approx 40 litres/week or 1 large grass box per week, filling about a quarter of the bin each time).
This will generate some odour that you may well notice for 2 days. If this bothers you, there are a couple of methods to solve this:
- add shredded paper or corrugated cardboard in ratio 2 parts grass to 1 part paper
- Only add half a box, then return 3 days later add the other half
|Grass volume / Weight
||To Avoid wet slime
||To Avoid Ammonia
|40 litre (approx 20 Kg)
||Add 2 litre (a measuring jug) of bulking agent. Mix in well
||Add 20 litre (a full carrier bag) of shredded office paper or chopped up corrugated cardboard).
Results in approx 1.6 Kgs of compost in 30-90 days
2) Large lawn – use a dedicated HOTBIN for grass
If you have a large lawn and generate 3, 4 or more boxes each week, then you will need to consider a dedicated HOTBIN. It will cope with 2-4 boxes (about 60-80L) per week.
The same rules apply – but adding and mixing in large amounts of paper is intensive and requires a high degree of commitment – perhaps not what you want straight after cutting the lawn! Large lawns allow the HOTBIN to be located away from your seating area – so we suggest you save your effort of adding shredded paper to eliminate ammonia odour – just leave the HOTBIN down the garden and reap the benefit of fast compost without anaerobic slime.
|Grass volume / Weight
||To Avoid wet slime
||To Avoid Ammonia
|80 litre (approx 40 Kg)
||Add 4 litre (a measuring jug) of bulking agent
||Leave remotely and accept ammonia for 1-2 daysAdd 40 litre (a full carrier bag) of shredded office paper or chopped up corrugated cardboard).
Results in approx 1.6 Kgs of compost in 30-90 days
3) Leave the cuttings to compost on the lawn
Many gardening sites now actively promote leaving grass cuttings on the lawn. Normally you use an adapted/special mower blade that chops the grass into very small pieces (2-5 mm) and thoroughly spreads them. The method is to weekly trim of top third of grass and spread this evenly so it composts quickly, adding nutrients back to soil, but not creating thatch. If you have the grass ‘trail line’ down side of mower, then this will rot into mulch that blocks light and growth and does create thatch. Please refer to manufacturer for correct mower blades/settings. If you walk regularly on your lawn – you may find bits get on your shoes and are walked back into the house!
4) Best of both worlds’
Add the first few cuts of the year which tend to be large (say 3-4 boxes) into your empty HOTBIN. The bin is full for a week or so, and then rapidly becomes half-empty allowing ongoing use with food. After the spring cut, leave grass cuttings on lawn. Occasionally (e.g. when cutting hedges) add the grass box back on the mower and collect grass to complement garden ‘browns’.
5) Transfer grass to Local Authority
This is unlikely to interest HOTBIN users, but it is possible to have grass collected at the kerbside and taken to the council recycling centre. We are strong believers in home composting and believe in the environmental benefits of saving fuel and transport.
6) Allocate a large, remote area of garden to build smelly grass mounds
The mounds will tend to be smelly and go anaerobic, but it is fast to empty and dump lots of grass. We had rave reviews on how fast and efficient the HOTBIN is with grass – so maybe you do not need this option anymore!
So in essence it is easy to compost grass in your HOTBIN but depending on the amount you need to consider which methodology is best for you.
This AUTUMN could be the time to RETHINK composting?
Autumn is coming – It’s will soon be time to start that big garden clear up again! Should you start to RETHINK your composting method now too?
You may well have wheel barrow loads of plant and weed being removed over the next few weeks.
What are you going to do with all your autumn garden waste?
1) Pile it all up as normal in that big heap – come back in spring hopeful of compost but most likely disappointed that you face the prospect of waiting another 12 months for your compost?
2) Take a different approach – join the HOTBIN composters and be sure of a fabulous batch of compost ready to dig in with you spring planting preparation?
3) Leave it out for the council green waste team to sort out – Oh dear! All that fuel, cost and effort to centrally reprocess it. Taking all that goodness from your soil this year, which means next year it has to be replaced by buying even more fertiliser, that takes even more energy and resources to make?
Composting during the cold autumn, winter and early spring months can usually be a very slow process. Especially when the temperature falls below 5C, the rate the bacteria work is almost nonexistent. The secret to fast composting is heat – and lots of it. Compost forms 64 times faster at 60C than it does at 10C. If you can keep your waste hot (between 40-60C), it will compost in 20 to 90 days!
There are many help sites that recommend building huge piles (minimum 1X1X1 m3), and then turning them regularly to keep them aerated and hot. But even this technique will struggle in winter as the heat produced by the bacteria is quickly lost to the cold air. (And it requires quite a bit of effort and space too)
This is why so many HOTBIN composters are happy – all the hard work to help support natural high temperature composting is provided by the HOTBIN. As long as you keep feeding it every week with enough waste – it will keep running at 60C. It has been tested and proven even with outdoor temperatures as low as -15C.
Not only can you get rid of all that garden waste, you will also be able to compost all your food waste over winter too.
Now if you were an early HOTBIN starter, your HOTBIN might be full already! If the bottom layer has been in there for 90 days, now is a good time to empty it to make room for your Autumn garden clear up.
It is always best to shred as much as you can (the smaller the pieces, the larger the surface area, the easier it is for the bacteria). Now if you don’t own a shredder then you can always use your lawn mower!.
Now you are ready to fill up HOTBIN to the top and get it back up to 60C .
If you have a large garden you may still have too much waste . So the best thing is to store it in pop up bag or on another heap. Remember to keep it covered to protect it from the rain. Where possible we suggest you store bags on stones/gravel so water drains out and some air can get in through the holes in the bottom.
You can add the excess waste every 4 days (about 20 litres 10 cms depth). As the ‘waste pile’ gets colder and older, reduce how much you add each week – But keep adding your food waste! (The bacteria need some easy to digest waste to keep the temperatures at HOT composting levels between 40-60C).
Keep going until all autumn waste is gone.
As soon as you start to collect a lot of autumn leaves – check out the ‘composting autumn leaves post’ as you need to tweak the recipe to hot compost leaves.
Remember the key to keeping it HOT is a BALANCE of ‘easy to digest waste’ made up of green stuff, food waste, plus shredded office paper’ (which creates heat quickly) with the hard to digest woody cuttings (heat released slowly), or partially composted waste (energy depleted).
Why not take up the challenge – find out what others have experience by visiting our ‘product reviews’ at www.hotbincomposting.com. Explore more about how it works by looking at our extensive ‘how to compost’ database, for example our ‘principles of hot composting’ article.
The HOTBIN is a simple design that helps maximise what nature does by bringing together the right conditions to make HOT composting easier. It does this by providing effective aeration between the bottom air inlet plate and the air outlet rotating valve, removing excess water through the valve as steam and allowing you to control the rate of heat loss.
How do I prevent maggots and flies getting into the HotBin?
The quick answer is “Get your waste hot (>40C) as quickly as possible”
Flies and maggots in the HotBin are a real rarity. They can occur and it tends to be when the HotBin is in the ‘set up’ phase before the temperature has risen above 40C. Below we explain why and how to prevent this happening. House flies and fruit flies can lay eggs in the your composting waste anywhere from the kitchen, kitchen caddy / bags holding waste and possibly at any time when the lid is open or the door is not fastened tightly.
A hot (above 40C) HotBin will kill all fly eggs, maggots and flies.
In our customer surveys 99% state they are satisfied or very satisfied with how the HotBin reduces and prevents flies – but we do get the occasional issue with maggots and flies and it is a guaranteed sign that the waste inside has not risen above 40C.
We do not believe there is a 100% sure way to prevent flies laying eggs in your compost waste, but the following will reduce the chances of them laying eggs:
Ensure the lid is tightly closed at all times (unless filing!)
- Ensure the door hatch is on tight and the cam belts have been used to pull the door on tight
- Cover all waste at all times (eg kitchen caddy, collection bags)
- Clear up any waste dropped around the HotBin – it will be a fly magnet
It is often the case that your waste already has fly eggs in it. Accepting this is possible, the next step is to prevent the eggs hatching into larvae / maggots. You do this by getting your HotBin Hot (>40C) very quickly (within a few days). Heat prevents any fly eggs hatching.
The basic technique is to add lots (at least half full) of ‘easy to digest’ waste (eg grass, food waste, shredded office paper, corrugated paper).
Quick tips to help you do this:
1) Add a box of grass mowing and mix into the waste already in the HotBin
2) If no grass, add 2-3 cups of either chicken pellets or chicken poo
3) Check excess water is not seeping from the aeration mesh in base – if it is, add half a bucket of cardboard pieces and half a bucket of wood chip (from black bag supplied).
You can find more information on getting to 60C in the PDF ‘how do I get to 60C check list’
Please note: you might occasionally have flies hovering around the valve or crawling on the door hatch panel. We can’t stop this. There is always some residual odour around the valve, and often some old compost on the door. They normally give up and move on when they are unable to find the food source that generates the odour i.e. they cannot find the place to eat and lay eggs. If they bother you and you are not adverse to using chemicals, then any of the fly/crawling insect sprays can be spayed on the HOTBIN parts to keep them away – but outdoors this is a bit of a losing battle – it will wash off in the rain quickly. But do try to keep the area free of dropped food & compost.
A text book start for the HOTBIN
The Compost Woman, who knows an awful lot about composting, reviews the HOTBIN! And I’m pleased to announce she has had a text book start as she has already reached 60C!
She started with an very full HOTBIN having plenty of material available for her base layer.
After 24 hours there was already a noticeable difference as the the material started to decompose.
She is a freelance Forest School Leader and Environmental Educator who works with both adults and children on all sorts of things. As well as a volunteer Master Composter and Master Gardener, helping people make compost and grow veg at home or at school.
There is more than ONE alternative to sending food waste to Landfill
Ban food waste from Landfill?
Collect and reprocess it via anaerobic digestion (AD) instead? Well yes and no!!
Respect the 3Rs: we should reduce food waste. Accepting there is always going to be some waste to treat…
There have been renewed calls to ban food waste from landfill in the Guardian today . The report’s co-author Quentin Maxwell-Jackson is reported by the Guardian to state: “Anaerobic digestion technology has so many clear advantages over other waste treatment and energy generation options that it is very surprising it has not taken off in a big way yet in the UK.”
Calls to ban food waste have been made before. The Government’s stated policy is collection and reprocessing food waste via AD.
It is still probably still too early for the policy makers to ban food waste from landfill as the UK does not have the capacity ‘coming on stream’ to reprocess it via alternative means.
Every new AD plant takes time to get planning permission, to build and commission. At out last reckoning, about 3 major were due to come on stream next year and we estimated the UK needed 300 to divert food waste from landfill – it is going to be a huge cost and long path.
AD makes a lot of sense – we need a collection/reprocessing technology that caters for the majority and we know only about 15-20% of the UK population does (or will) home compost and traditional home composting has never been appropriate for all food waste.
We should not let the historic issues of home composting all food waste (including cooked food, meat, fish, bread, cakes, rice, pasta etc) that create a stinky odour that deters people and attracts rats, flies from continually reviewing technology for home composting. The HOTBIN team has real factual evidence that the HOTBIN has changed home composting of food waste for the better. Users have changed behaviour and are diverting all food waste from landfill. We estimate 5m current home composting households could divert all food waste and make a contribution – immediately.
100,000 HOTBIN users would equate to 1 new big AD plant. Delivering a million units a year (we wish!) is a logistics co-ordination issue – the capacity can be made available very quickly. We understand home composting is not for everyone – but we need to make a dent in landfill now and it can be done now.
There are other reasons why AD is not the ‘be all and end’ of reprocessing food waste. Reprocessing is a complex combination of user behaviour, logistics and technical facts. Yes AD has advantages, but so does home composting. Home composting removes the need for collection and transport, the compost can be used in the garden (reducing fertiliser and peat consumption) and adding organic matter and humus back to into soil is essential to soil fertility.
Help us win government support – HOTBIN composting diverts domestic food waste.
[At present we are pushing water up a hill and knocking on closed doors.]
How to compost ALL food waste
Below we explain how to Compost ALL domestic food waste
(i.e. at home, in a garden, or via backyard composting).
Why do we need this blog?
Surely food waste is just like other waste for composting – we just add it to the compost heap and it breaks down?
What’s the big problem? Well to a degree this is true, food waste is carbon/organic and will compost. The problem is NOT that food waste does not compost, it’s just that more often than not, it creates a putrid stinky mush that attracts rats and flies.
What are the specific issues with food waste composting
Here at HOTBIN Composting we talk to a lot of people who compost – from Master Composters, Council Recycling Officers, expert gardeners to complete novices and we have also read hundreds of composting forums and blogs: the advice is near universal: ‘do not add meat, fish, cooked food waste, mouldy bread, left over bones, cakes, bits pizza, chip boxes, dairy products, gone off fruit, out of date fridge contents to your compost heap. If you do, they will rot, produce putrid odour which in turn will attract vermin and flies. Only add kitchen peelings and tea bags,coffee grinds’.
Kitchen peelings,tea bags, coffee grinds only account for 40% of domestic food waste.
The other 60% falls into the “do not” add to a compost heap.
[We know this because very detailed waste analysis of what goes in our disposal bins and onto municipal refuse collection and landfill was undertaken by the Love Food Hate Waste campaign in 2011 (recycle Now, WRAP) . Teams of people sifted and weighed the contents of 1000’s of household waste bins over many months (nice job!). So we know on average, a UK household produces 250Kg/year of food waste. Every item wasted was listed and weighed (what they call a composition analysis), so it is easy to look at the list and reclassify per the compost “in/out” list.]
So even those with a compost bin, will most likely still be sending food waste to landfill.
They might still have stinky food waste sitting in a kitchen or wheelie bin for two weeks. (We accept there is a growing number of councils rolling out kerbside collection to be used in AD/EfW recovery plants – but this is a small part of the total).
Millions of home composters want to add ALL food waste to their compost bins.
This is what why the HOTBIN was invented: ‘to create a compost bin and method that enables millions of existing home composters to compost ALL food waste without the inherent problems of odour, vermin and flies’
Why does food waste rot and go putrid
As food waste starts to breakdown it forms a thick slimy mush. This soft mush prevents airflow and so the waste quickly turns anaerobic. As soon as anaerobic bacteria take over, the waste releases putrid gut wrenching odours. From here it is all downhill – the smell attracts vermin and flies and everything becomes unpleasant. As food is composted, the structure/fibre of the food weakens and water is released. There are three places the water can go – it can drain to the ground, it can be driven off as steam (water vapour) or it can remain in the waste. Under most composting conditions the water stays in the waste until it becomes saturated and then it will start to drain into the ground. Composting soft food waste naturally produces a mushy slime.
The alternative is to use heat produced by the bacteria to drive of water as steam vapour. This happens when we hot compost.
The golden rules for successfully composting ALL food waste are:
- Remove excess water
- Keep the waste aerated
What is composting?
The biggest part of the composting process relies on bacteria and if you refer to our post So What is Composting? you will note their requirements are not dissimilar to what humans need to survive and grow!
So how do we get rid of excess water and keep the waste aerated?
We take a lead from industrial composting and apply the science and engineering they use to a domestic compost bin.
(If you want to look up the science and engineering, have a read through Haug – Practical Handbook of Compost Engineering) on Amazon book review.
Let’s cut to the chase
- To remove excess water
You need lots of heat i.e. you need to be ‘HOT composting’
- To aerate you need to keep adding lots of oxygen/air
Unless you have the means to force airflow (e.g. a pump / blower), or you can constantly turn/tumble (yes we mean constantly), then you are reliant on “buoyant airflow’ or the chimney principle of hot air rising creating a pressure drop that pulls cold air through from below. You only get buoyant airflow if there is a temperature gradient – i.e. you need heat.
- To maintain buoyant airflow (even with heat)
You need to a heap structure that maintains buoyant airflow. To get a structure that stops food waste collapsing into a mush you need to add what we refer to as a bulking agent (typically this is wood chip).
In summary to compost food waste, you need to get the waste hot, aerate it (via buoyancy airflow) and ensure it stays aerated by adding a bulking agent. It sounds technical and it would be easy to achieve where it not for nature’s laws on heat production and heat loss!
Nature has a law on how much heat is produced
Bacteria release heat as a by-product when they ‘eat’ the waste– just like humans release heat when we eat and exercise. The amount of heat is capped by the calorific value – the more calories the more energy and potential heat. The rate of heat released varies by food type.
Think of it like this human analogy – eat coke and sweets (sugar!) for breakfast and you’ll be on a sugar high for a few hours, then hungry again. East oats/muesli and it will be digested more slowly but over a longer period – you’ll make it to lunchtime.
Bacteria are the same – they digest and release heat from sugars and carbohydrate food very fast, from cellulose (plant material) slower, and from lignin (wood) even slower. The amount and rate of heat generated is determined by what goes in and how much goes in. For most households – it is a challenge to create a hot compost heap, you need about X10 more food waste than most households create.
Nature has a law on how much heat is lost
Heat transfers from a hot place to a cold place until they both reach equilibrium, i.e. the same temperature. This law is scientifically defined by Newton’s law of cooling. Let’s simplify it for a compost heap – even in summer (25C), a compost heap will not stay hot (40-60C) for long as the heat rapidly moves to the cool air. If you want to keep your waste hot, you need to reduce the rate of heat loss ie you need to insulate it. There are two ways of doing this – by having a large heap so the outer metre of waste acts as insulation or use a specialist insulation material.
Oh, one last thing – odour, vermin and flies
Lets assume we are now hot composting away. All composting creates odour and food odour attracts rats and flies. Unless you want a heap infested with rats and flies then you are going to need to control odour so it does not attract vermin and control access the compost heap just in case. In other words, compost in a container that won’t attract rats or let flies in.
Successful food waste composting needs heat (for water removal), oxygen (to ensure aerobic bacteria active), which in turn needs a heat gradient, which needs bulking agent to allow airflow. We need to balance the heat produced with the rate of heat loss (insulation, protection from wind) to keep the bacteria warm and composting fast and then protect the whole operation from infestation with rats and flies.
Achieving the above without a specialist bin is very hard.
The HOTBIN was specifically designed to achieve HOT composting to allow ALL Food Waste to be composted. To find out more please visit our extensive FAQ
So what is composting?
What is composting and how does it work?
The composting process relies mainly on bacteria ‘eating’ the good and garden waste. Aerobic bacteria require;
- Food and minerals
Open this document to see how the different requirements affect the composting process.
Not dissimilar to what humans need to survive and grow!
Warmth is not that widely understood. The speed of composting is directly related to how warm the bacteria are.
At Zero C – they are frozen and little happens. They work faster all the way to 75C. We normally describe composting as either ‘HOT’ ( 40-60C) or ‘COLD’ (>20C).
In most outdoor UK compost heaps, over the year the average temperature achieved will be 10C – i.e. the same as the ambient UK average temperature. There are many things that have to be right for composting to occur, but when it comes to how long it takes, there is one overriding factor that affects the speed (rate) at which waste decays and this is temperature.
In very simple terms for every 10C increase in temperature, the speed doubles. So if the average UK temperature over the year is 10C and we call this speed 1; at 60C (HOT), composting is 32 times faster.
To compare this on average you will find a UK open/outdoor heap typically takes 12-24 months to compost. If the same material was composted at 60C, it would take 12-24 days.
That is the real difference between COLD composting and HOT composting!