Tag Archives: balancing carbon/nitrogen ratios

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

Speed
(At 60C)

Material Notes

Fast
(days)

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.

Fast
(days)

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)

Newsprint/papers
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.

Medium
(weeks)

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