Tag Archives: cold composting

How and why do I use corrugated cardboard and shredded paper in the HOTBIN?

Recycling Food Waste in the HOTBINDry corrugated cardboard and shredded paper is easy for composting bacteria to digest (see table below).

Because they are also very ‘dry’, i.e. have very low water content (typically less than 5% water), they are the best materials to add to wet food waste to balance things out and ensure there is enough heat to drive off excess water as steam.

By the way this use has nothing to do with aeration and very little to do with balancing carbon/nitrogen ratios!

(Please note – Ignore the advice on many cold composting sites that scrunched up newspaper and or cereal packet cardboard will provide aeration – in the HOTBIN they WILL NOT create aeration pockets – quite the reverse – the paper and card will be soaking wet within hours and form a matted impervious layer to airflow. It is highly likely the newspaper will come out when you empty the bin as a flattened blob of soggy newspaper.

It is essential you mix both the paper and the cardboard into the waste rather than just add it in as a layer on the top. When adding food waste ALWAYS also add bulking agent. The bulking agent will form a supportive structure (think building blocks) around which air can flow.

Why will paper and corrugated paper compost quickly but not newspaper?

It is easy to think all paper products come from wood so they should all decompose at the same rate.
We know that thin high surface area materials will decompose faster – so cardboard is faster than a wood branch piece as the bacteria have more surface area to attack. If we assume and example where surface area is the same and the temperature is the same, the speed at which wood products compost is directly related to the amount of lignin contained – so hard wood decompose slower than soft woods.

We can take this analogy a little further to explain newspaper and white office paper – the comparison is made in the table below.

Comparison table

(At 60C)

Material Notes


White paper (e.g. office, A4 copier, coffee filters) The caustic part of the Kraft paper pulping process removes lignin to leave only cellulose fibres.Shredded it rather than crunch it up. Sprinkle in little and often – thick layers will quickly get wet and form an impervious mush that prevents airflow.


Corrugated brown cardboard boxes, egg cartons Although processed, about 5-10% lignin remains.Corrugated cardboard has the advantage of trapped air/air channels. Shredded or tear up – large sheet will block airflow

Medium (weeks)

Cardboard sheets
This is low cost paper – the expensive lignin removal stage is not undertaken – it is small wood fibres. (Compare to white office paper above).Ensure shredded or scrunched up. It will compost far more slowly than food, grass and most other wastesDo not add whole cereal boxes – tear up and spread / mix into waste. Add sparingly – if attempting to dry wet waste, much better to use office paper or corrugated cardboard.


Gloss printed,
waxy papers
Wax coatings are slow to decay. Higher temperature allows addition in HOTBIN

How do I create lots of chopped up cardboard quickly?

 Everyone tends to have corrugated cardboard boxes, but tearing them up can be tiresome. You can quickly cut into strips using a craft or Stanley knife – but you need to take care and do this correctly to avoid taking your fingers of! A safer way is to see if your office shredder is a ‘multi sheet’ unit. If it is it will shred 8 sheets of paper at a time and you will find it will shred most cardboard boxes. See photo’s below. Please keep in mind if you put too much strain on a low sheet feeder it will just overheat and conk out!

A useful post on dealing with excess water in the HOTBIN can be found on our online FAQ : Excess Water Post

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Filed under Hot Composting, How to get the best out of your HOTBIN, Recycling Food Waste

Compost – Looks can be deceptive!

What comes out of your compost heap, compost bin and indeed your HOTBIN can vary an awful lot.

With many HOTBIN® composters coming up to their first autumn, there will be a lot of hot compost being taken out and used in the garden. We thought it would be good idea to let you know what to expect as ‘looks can be deceptive’!

To do this we will look at several batches of compost alongside some HOTBIN composts. Suggest how they might be graded based on common expert visual assessments. Then we will take you on a journey beyond the first look to give you some insight into compost stability and maturity tests (we’ve done them for you!), discuss what happens when you dry and sieve HOTBIN compost (don’t worry no-one is suggesting you need to do this) and finally do a bit of mud pie play to demonstrate a property called ‘colloidal behaviour’’. Finally we will tie these properties back to humeric substances and suggest that what you really need to look for in fabulous compost is high humeric substance content.

This blog is a little more scientific in nature than some of our others – so if you want the headline without the science it is this:

What a compost looks like can be deceptive. HOTBIN compost is often very sticky and very moist/wet and looks lumpy and perhaps even needing further composting. Tests show rather than it being ‘poorly’ composted, quite the reverse – it appears to have a very high humeric substance content and this is good news for your soil and plants – humeric substance is known as ‘black gold’ for a reason!

If your compost looks like (Fig 4&5), or even (Fig 6) below it is OK to dig in to your soil and does not need ‘more composting’. If you only want ‘fine’ particles of compost e.g. looking like (Fig 1) or (Fig 2) – the solution is fairly simple – dry your compost and then sieve it – you will surprised by how much fine material there is in HOTBIN Compost.

Our analysis tour includes;

1. Visual inspection

2. Carbon / nitrogen maturity test

3. Visual after drying and sieving

4. Pliability / colloidal behaviour

5. Humus test

6. Result to quality – is it fabulous?

1. Visual inspection – Below are 6 samples of compost 

(Fig1) Vermicompost

(Fig1) Vermicompost

(Fig2) Garden centre compost laid out dry

(Fig2) Garden centre compost laid out dry
(Fig 3) Typical cold compost

(Fig 3) Typical cold compost

(Fig4) HotBin compost at 3 Months

(Fig4) HotBin compost at 3 Months
(Fig5) HOTBIN compost that is it too wet

(Fig5) HOTBIN compost that is it too wet

(Fig6) HOTBIN compost that has gone anerobic

(Fig6) HOTBIN compost that has gone

anaerobicNow in our earlier blog (good, bad or fabulous compost) we outlined details on how different experts defined good compost. If we asked this group of experts to visually judge the samples above here is what we would expect:

(Fig1) Vermicompost – looks fine and rich, super

(Fig2) Garden centre compost laid out dry – looks very fine and free flowing, uniform and has probably been sieved

(Fig 3) Typical cold compost – looks mature, maybe 2 years old and as expected,

(Fig4) HotBin compost at 3 Months – looks ok, dark brown and a little lumpy

(Fig5) HOTBIN compost that is it too wet – looks water logged, lumpy, immature and soggy

(Fig6) HOTBIN compost that has gone anaerobic – definitely looks anaerobic, it’s black sludge not compost

2. Carbon / nitrogen maturity test

Industrial producers of compost (i.e. compost sold in garden centres) do a check to establish how active the bacteria are. Above a certain level and the compost is too active (i.e. not mature & stable) it needs to be left longer otherwise it can draw nitrogen from the soil as bacteria continue to use the carbon in the remaining compost. The maturity and stability test can be undertaken via the Solvita compost test method. You can do these at home, although it gets expensive!

Garden centre compost (Fig2) would not have gone on sale without passing the C/N maturity and stability tests. How did HOTBIN (Fig4&5) compare? Well they both fall in the stable and mature range. This will surprise a lot of experts as they look lumpy and lumpy normally means large pieces of non-composted material which is highly likely to result in an ‘active’ rather than stable result.

3. Visual after drying and sieving

We recently tested a range of compost sieves (see guide to compost sieves post). We know wet and sticky compost is a complete pain to sieve. When testing the Compostsifter it failed to sieve any of HOTBIN (Fig5). So we dried the compost and tried again. This reminded us of an old saying – ‘looks can be deceptive’. Below is the result of the sieving test.

HOTBIN compost sieved

HOTBIN compost sieved

The result was about 80% of all the compost went through the fine (8mm mesh) sieve. There is about 15% of wood chip pieces (0.8-1.5mm), and 5% oversize non-composted items (notably pampus grass roots – these are possibly going to take the record for the hardest most difficult material to compost – but that’s another blog!). I’d just like to say this sieve result is not a one off – we have seen it many times, same results.

If we visually compare the sieved HOTBIN compost with the sieved garden centre compost they now look very similar. So was the problem just that the HOTBIN sample has been stuck in the base and got wet? Is the difference just about one compost being very wet and another compost being dry? No!

4. Pliability / colloidal behaviour

When we sieve and handle HOTBIN compost we notice something else – it is very sticky. It rolls into balls in the sieves, when you grab a handful you can make a ball. It is ‘pliable’ just like a potter’s clay or children’s plasticine.

HOTBIN Vs Garden Centre on compost pliability

HOTBIN Vs Garden Centre on compost pliability

There are two common substances in soils and composts that create a pliable mix – clay and humeric compounds. Both these are ‘colloidal’ materials and it is this property and the resultant way they hold water that leads to the pliability.

We can take the pliability test a little further. If we make a ball of moist compost from Garden centre compost and HOTBIN compost (Fig5) and leave then to dry in the sun for 4 days. Now what happens when we try and squeeze each ball?

HOTBIN Vs Garden Centre - compost pliability after drying

HOTBIN Vs Garden Centre – compost pliability after drying

The garden centre compost sample behaves more like peat – it sticks when wet, dries fast (i.e. looses water 2-4 times faster) and then the organic material falls apart when the dry ball is pressed. Whilst the HOTBIN sample is still damp and pliable, it forms a very hard solid outer layer material with soft inner. Even after 100% drying and re-wetting the pliability returns.

At this stage we should mention that HOTBIN composting (and certainly the batch of HotBin compost above ) had no soil added – hence the pliability is not believed to be due to soil clay.

5 Humus test

We think (and we mean ‘think’ because we have no laboratory proof) that it is possible that HOTBIN compost has more humeric substances than many other composts.

HOTBIN compost - Pliable humus

HOTBIN compost – Pliable humus

Can we test for humeric substances? The answer is yes but not easily outside a fully operational soil testing lab. There is a relatively simple humus soil test – targeted at measuring the concentration of humeric substances in soils. The HOTBIN samples are off the scale – but a note of caution – the test aims to give a reliable field test for soils with 0.5-6% humeric substances. It cannot be relied on for concentrations well above this.

6 Result to quality – is it fabulous?

We believe there is a real difference between compost and compost that contains very high amounts of humeric substances. Partly decomposed material (compost) will continue to decompose when added to the soil and eventually the carbon cycle completes and it is returned to carbon dioxide and a small amount of recalcitrant humus in the soil. Humeric substances do not decompose in the soil (to any great extent) so adding a concentrated form will improve your soil faster.

HOTBIN compost - drying out

HOTBIN compost – drying out

As a company we are not into making claims about our products we can’t substantiate – to be clear – we believe we can explain the appearance and behaviour of HOTBIN compost. We believe we can trace (but not prove it yet!) this back to higher humeric substance content in HOTBIN compost. One day we will have the evidence – until then we believe our logic and science has merit, you can do your own testing, contribute to the debate or ignore our findings as just marketing waffle!


Filed under Compost, How to get the best out of your HOTBIN

HOTBIN investigates an interesting composting method

We had an interesting question come in last week!
Was Black Soldier Fly (BSF) composting the most efficient composting system ever?

After many years in composting, we had not come across BSF before, intrigue and a hint of competiveness that any system might be better than the HOTBIN, we did a bit of googling. You learn something new every day!

  • BSF (Hermetia_illucens) is a species of fly with native to America (with a cousin down in Australia). There will be a UK entomologist who will no doubt identify a cousin in UK, but so far not aware – and hence possible reason we have not come across them in UK)
  • It has a niche habitat – rotting food/manure. The fly lays eggs in compost and the larvae (some would say maggots) eat the food waste – and they appear pretty good at it. (This is no different to house flies and or vinegar/fruit flies – BSL are much bigger and eat more!)
  • The larvae are not meant to be allowed to hatch into flies (ie pupate), they are collected and used as chicken feed and/or fishing bait
  • There are a number of specialist bins designed to house, retain and harvest the larvae. As a food waste disposal system, it more closely resembles worm composting.

What about claims to be the “most efficient”? We are always suspicious of ‘fastest and best’ and try and uncover the scientific facts. There was no reference to a specific quote and we did not see the claim on sites listed below. It looks like there is enthusiasm for BSF, as highly efficient and this enthusiasm comes from the visible disappearance of food waste as BSF larvae eat food within 2-4 days. If you compare 4 days to “composting” even hot composting at 30 days – you might think it’s more efficient. But decomposition (eating waste food) is just a set of biochemical reactions involving enzymes – the rules are fixed: the rate at which reactions take place is governed by the Arrenhenius equation – which basically boils down to temperature. BSF Larvae die at 40C, thermophilic bacteria operate at 60C and in many cases 70C.

In simple terms, larvae at 40C work at the same speed as bacteria at 40. If we say composting at 10C is rate X1, then larvae and bacteria at 40C are X8 times faster, but bacteria at 60C are 32 times faster – speed wise, we think no contest!

But is speed what we need to focus on? What are we trying to accomplish? Are we seeking to dispose of food waste fast, make fish bait or make great humus with high nutrient and water holding capacity that dramatically improves soil fertility? (With the added plus of diverting food from landfill).

Nature eventually recycles all plant and animal matter back to carbon dioxide and water. Does it matter if the larvae eat food, then the chickens eat the larvae and then the bacteria eat the chicken poo? Or that the bacteria eat the food (and release carbon dioxide), but leave some residual waste (compost) that gets eaten much later and then finally becomes carbon dioxide. Both routes are carbon neutral and better that sending it to landfill where it will decompose anerobically releasing methane.  BSFL larvae eat the food and produce a small amount of residual compost like material. Composting and hot composting produces a lot of compost for the garden. Compost is beneficial to the soil before it is finally returned to carbon dioxide.

We should perhaps note that for many humans, the reaction (rightly or wrongly) to flies, larvae & maggots are negative. Even though BSF appear as good guy (does not bite, sting or carry diseases problematic to humans), we know from experience (backed up by surveys), that one of the biggest reasons people stop composting is flies and maggots. The prospect of actively promoting lots of maggots in waste food seems at best destined as a specialist area.






Filed under Compost