Your First Batch of Compost: The Base Layer

23 September 2015  |  HOTBIN Composting

Your First Batch of HOTBIN Compost

When you remove your first batch of compost (your initial base layer) from your HOTBIN, you may find that some or all of this material needs to be reprocessed. This is due to lack of heat within the bottom of the HOTBIN in the very beginning of the process. Subsequent material should not require reprocessing unless the unit has been operating at temperatures consistently below 40°c.

The base layer stays cool as cold air is pulled in through the base plate and up to the hottest layer at the top, before rising out via the valve as water vapour. Even if the top has been running at 60°c, the very bottom has only been composting at around 5-10°c.

What’s in a Base Layer?

All wastes have different rates of digestibility; for this reason, we recommend adding lots of easy to digest waste when starting your HOTBIN. Easy to digest waste provides the hot composting bacteria with a quick supply of food which when digested, causes internal heat to be generated rapidly as a by-product of the digestion and decomposition process.

Without the addition of fresh waste in the HOTBIN, heat cannot be produced and so some harder to digest wastes may not be broken down sufficiently in the 30-90 days time scale. As a result, these types of material will need to spend longer in the HOTBIN to fully decompose, whereas easier to digest waste types may produce usable compost.

No fresh waste = No new heat.

In summary the warmer bacteria are the happier they are and the quicker they work.

What Should My First Batch of Compost Look Like?

So you may be expecting this:

Matured compost beinf romoved from the base of HOTBIN

It is extremely unlikely you will see this with your first base layer due to the science above. It is more likely to fit somewhere in the range of the five HOTBIN base layer photos below. All these are from HOTBINS where the upper layer has been composting away at 40-60­c for 10-12 weeks, the waste has not fully composted in any of them, but they are all subtly different.

Let’s take a look..

1) A reasonably good base layer batch ready to be removed and used straight away.
Good base layer removed from HOTBIN after 10-12weeks







2) Blackish, compressed compost, quite wet and sticky.

Black, wet and sticky base layer removed from HOTBIN after 10-12 weeks

3) All brown, but still some visible pieces.

Brown with visable pieces base layer removed from HOTBIN after 10-12 weeks

4) Brown/black, wet and sticky, might be oozing water.

Brown/Black base layer oozing water removed from HOTBIN after 10-12 weeks

5) Some green bits, clear pieces

Base layer with some green bits and whole pieces removed from HOTBIN after 10-12 weeks

My Base Layer Looks Like One of the Photos. What Should I Do Next?

We advise “reprocessing” the base layer to finish the decomposition process.  Our advice differs slightly depending on how the base layer looks.

My Base Layer Looks Like Images 2 & 5

Black, wet and sticky base layer removed from HOTBIN after 10-12 weeksBase layer with some green bits and whole pieces removed from HOTBIN after 10-12 weeks

  1. Pull out the base layer (1/3 of the waste in the HOTBIN)
  2. Mix in ½ a carrier bag of shredded paper/corrugated card
  3. Mix in three double handfuls of bulking agent (woodchip)
  4. Add base layer back into the top of the HOTBIN ensuring this is mixed with a caddies worth of fresh easy to digest waste (food is best) and the correct ratios of shredded paper and bulking agent for the fresh waste.

Note: This fresh easy to digest waste will need to be well incorporated to ensure bacteria is spread evenly throughout the whole waste. Bacteria will start to break down the easily digestible material first and generate heat more rapidly before spreading and moving to the base layer waste which will be harder to digest, resulting in a slow release of temperature inside the bin helping to sustain hot composting temperatures.

  1. Put it all the waste in via the top. Temperatures should  rise to 60°c initially for a couple of days then settle down to 30°c.
  2. Carry on adding new waste as normal with shredded paper and bulking agent.
  3. Look at the second base layer in 8-10 weeks and there should be compost ready to use.

My Base Layer Looks Like Images 3 & 4

Brown with visable pieces base layer removed from HOTBIN after 10-12 weeksBrown/Black base layer oozing water removed from HOTBIN after 10-12 weeks

Take out the base layer now and use it for digging into beds/vegetables.

Why Can’t it be Reprocessed?

There is very little “fast food energy” left for bacteria so it is unlikely to reheat. If the base layer smells sour all it not lost, DO NOT throw it away – just spread it out on a ground sheet and leave in sun for a day or so. It will re-aerate, lose its smell, dry and be easy to separate the large lumps from the small. If there are parts that are not well broken down add these back into the top as per instructions above.

General Advice on Reprocessing

Sometimes, you may find the odd item in any batch of compost that requires a little longer in the HOTBIN to decompose fully. These odd twigs, pieces of eggshell or bone can be added straight back into the top of the bin with some fresh waste.

Remember to always add in bulking agent and shredded paper/corrugated cardboard each time new waste is added to the HOTBIN. If the new material is already partially composted (e.g. if it is from another composter), fresh waste should be added too to provide the bacteria with access to easy to digest food.

Remember. Don’t Be Disheartened!

Our aim is to be realistic and make sure you are not disappointed with your first effort.

Everyone’s base layer is different and dependant upon what is readily available at the time of year you start composting. Just remember that it’s the base layers job to get your HOTBIN off to a good start!

You can find out more about what to expect in subsequent batches of compost by reading how does HOTBIN compost look and feel?