Tag Archives: hotbin

Hot composting – not so hot

Becky and I are obviously very keen to produce as much of our own compost as possible, given how much land we’re trying to keep nicely fertile. I’ll be writing about plans for composting all our garden waste in a later post, but here I want to talk about composting our food waste.

Almost anything you can eat will compost down eventually, but a lot of food waste isn’t put onto traditional garden composters because it will attract rats and other nasties. Moreover, some composting advice indicates not to compost meat, for instance, as it will not break down properly.

However, some modern plastic composters are designed to be used with food. They are protected from pests and designed to build up heat to a level where even meat will break down quickly. In theory, that is.

You-will-be-composted!

At our previous home, we had a Green Johanna, a bin shaped like a dalek which claimed to be able to compost food. We merrily chucked in whatever we felt like – peelings, stems and so forth, of course, but also leftovers, bones, and more. Perhaps unsurprisingly in retrospect, this did not compost terribly well, and attracted lots of flies that seemed quite happy to live inside the compost bin. It didn’t get hot. We did eventually get out some very compacted, muddy stuff out of the bottom which seemed to have broken down ok, but took a very long time about it.

Once we arrived at Westwick, we discovered that the local council did not do food recycling (an oversight they have recently rectified), so that all our food waste would have to go to landfill. Naturally we were keen to get composting again as soon as possible, but wary after our experience from before. I decided to invest in a Hotbin, which is essentially a massive hollow block of polystyrene with airvents.

A shiny new Hotbin.

With the Hotbin, I got a bit more serious about composting. I read up about what you should put in, brown vs green waste, nitrogen-rich vs carbon-rich, and so forth. I realised that it wasn’t at all surprising that our Green Johanna had failed to come up with the goods; indeed, it was us that had failed, not the composter. A few things we got wrong:

  • Not including sufficient “brown” waste i.e. wood and other high-carbon material.
  • Not cutting up either the “green” or the “brown” waste into small enough chunks (we would throw whole pineapple tops into the composter, for example).
  • Putting things in the composter, like bones, that would take too long to compost even at high temperatures.

It took us quite a long time to get started with the Hotbin, even so. The instructions say you need a “base layer” 40cm deep to get it to heat up. This turned out to be quite a lot of waste, which, built up over time, didn’t then magically get hot straight away. Once again, we underestimated the amount of brown waste required, by a significant margin. However, once we had realised our mistake, we started adding a lot more, we got the composted cooking, and soon it had reached 40 degrees C, and later 50 and even occasionally 60. These are the temperatures you want to reach for hot composting. We have been using straw from our pigs as brown waste, which certainly seems to do the trick temperature-wise.

Digging this lot out took quite a while.

Digging this lot out took quite a while.

Nevertheless it took too long to get started and the waste at the bottom of the composter never heated up – we were composting at the top but with putrifying food at the bottom. I dug the base layer out , let it dry for a couple of hours and returned it to the composter with large amounts of brown waste added.

Since that time we’ve had the composter operating at a high temperature most of the time. But for whatever reason, the bottom layer is still not fully composted – and has gone compacted and cold. There is a significant amount of uncomposted food amongst what looks like otherwise decent compost. Brown liquid has been leaking out of the bottom, with a smell not altogether dissimilar to raw sewage, and the “compost” itself stinks – not a good sign. We still don’t have anything we could put on our garden, and the composter is pretty much full.

Not what our compost ought to look like.

Not what our compost ought to look like.

I’ve had to dig it out again, and because of the weight of material above, this meant digging the whole thing out, since as I dug out the waste at the front, the stuff above collapsed down blocking access to the older waste at the back of the composter. This time, I’ve waited for a sunny day and laid the waste out on a tarpaulin to dry in the sun. I’ve put it back in with a bit more straw added, and am hoping this will do the trick.

If not, there’s one more trick to try. The instructions for our Hotbin mentioned using shredded paper as “dry” waste to balance out the “wet” waste (i.e. cooked food). We had been assuming that straw would be perfectly good as a substitute since both appear to be “brown” waste. But we’re now wondering if the paper’s absorbency helps to mop up excess fluid in a way that straw can’t. If necessary, I’ll dig it out a third time and add shredded paper.

Our Hotbin is now completely full, and indeed I’ve had to put some of the waste from it into the council’s food recycling bin to make space for additional straw. We’ll have to throw things into the recycling that we would have liked to compost. It has been quite a learning curve and we still haven’t mastered it. I’m hopeful that we’ll get there in the end, but at the rate we’re progressing it may be that we will have had our Hotbin for a year before we get the first usable compost out of it.