My compost is too wet, what can I do?

Friday, 16 March 2012  |  HOTBIN Composting

Waste Too Wet to Hot Compost

Sometimes it can be a bit of a struggle to get the HOTBIN up to 60°c. One of the most common issues is the waste is "too wet" for hot composting. In this post we explain what this means and how to fix it.

The advice below might not match your past composting experience. Please stick with us, this advice works, it is based on the fundamental laws governing hot composting. Once grasped, you will find the HOTBIN easy to use for ever.

What does ‘too wet’ for hot composting mean?
You have more water in the food waste than energy (calories/heat) available to evaporate the water as hot steam. If you do not balance a wet mix, the waste will not get above 40°c, it will turn smelly and a lot of leachate will drain from the base.

Is my waste 'too wet' for hot composting?
It can be a challenge to find out. You are not looking at the waste to see if it 'dripping wet'. The waste is 'too wet' when the total percentage of water contained inside the waste cells is above 75%. As a rough rule of thumb:

  • Garden waste have 40-60% water content
  • Vegetable peelings have 70% water content
  • Food waste is on average is 80% water content
  • Foods like salads, juice pulp and cooked food have 90% water content

What are the signs my waste is ‘too wet’ for hot composting?

  • Lots of leachate (brown water) leaking from mesh plate. (Check the water is definitely seeping from behind the mesh plate, ignore condensation and lots of water dripping off the inside of lid when you open it)
  • The waste in the HOTBIN smells putrid, rancid or drain like (i.e. it is anaerobic)
  • The temperature in the top layer will not increase above 30-40°c. (Poor aeration and lack of new waste also prevents temperature rising above 40°c – so check these as well).

TOP TIP
Always investigate and fix excess water issues – the sooner you address, the easier it is to fix. Sorting out an anaerobic smelly mush of partly composted food waste is just about the worst composting job there is.

How do I fix (balance) waste that is 'too wet'?

  • By adding a dry ‘easy to digest’ waste into your mix. The easy and available material to add is shredded office paper/corrugated cardboard which helps absorb excess moisture. For information on shredded paper to wet/food waste ratios view how much paper do i need to add to food waste.
    (Avoid adding newspaper or cereal packet card for this task. They are not easy for bacteria to digest and will just end up as a mushy lump in your final compost.)
  • Adding a bulking agent. This should always be added with all waste to aid airflow within the HOTBIN. Bulking agent to waste ratios can be found here.

Remember: Shredded paper is to balance the moisture content in the waste and bulking agent is to maintain aeration. Both are essential to hot compost effectively.

TOP TIP
Half fill your food caddy with paper and add the waste on top.