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:
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.
2) Blackish, compressed compost, quite wet and sticky.
3) All brown, but still some visible pieces.
4) Brown/black, wet and sticky, might be oozing water.
5) Some green bits, clear pieces
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
My Base Layer Looks Like Images 3 & 4
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.