Odours Coming From The HOTBIN

All composting produces odours.The ability for the human nose to detect them depends on the concentration in which they are released. This in turn depends on how much waste is decaying and at what rate (i.e. cold or hot composting) and other factors such as temperature, humidity and wind speed.

The HOTBIN has a built-in carbon filter in the lid which minimises all odours.

What Should my Compost Smell Like?

This will depend on the age of the compost (fresh or mature), and whether it is working aerobically (with oxygen) or anaerobically (without oxygen). The different types of compost odours, what causes them and how to limit or reduce them are explained below:

The Four Main Composting Odours

1. Cabbage / Fruity Odour | Normal in all composting
   
   Explained: A fruity boiled cabbage type odour; is a sign of a highly efficient HOTBIN. This odour is due to bacteria breaking down complex sugars and cellulose into smaller chemical compounds rather than carbon dioxide. These hundreds of chemical compounds vaporise (become odorous gases) and are given the collective name of volatile organic compounds (VOC’s). At hot composting temperatures of 60°C, VOC’s are produced faster and vaporise quicker leaving the HOTBIN via the valve. The HOTBINs filter pack in the lid help reduce these odours below nuisance levels. However, there will always be a short whiff each time the lid is opened. In cold composting, these chemicals are produced slowly and do not vaporise to the same degree, hence why you rarely notice them.
   
   
2. Ammonia / Urine Odour | Excess nitrogen in mix
   
   Explained: This odour is created when excess nitrogen leaves the heap as ammonia gas. You are most likely to notice this when composting large quantities of 1-2 day old grass mowing’s. When you turn a pile of grass you will often notice the odour when you get indoors as it has clung to your clothes. Read more about grass.
   
   
3. Putrid / Rotten Odour | Lack of oxygen
   
   Explained: These odours are associated with anaerobic heaps. There are a wide range of chemicals including valeric acid (sick), hydrogen sulphide (bad eggs), dimethyl sulphide & acetic (vinegar) that are described as sour, acidic, and very unpleasant smells, which create a natural "gut wrench" reflex in humans. It is believed this is a defence mechanism to prevent us eating rotting dangerous food. This is a group of odours you do not want. Not only are they unpleasant but they are a robust indication that the compost bin has turned anaerobic, and you will eventually end up with a wet slimy mush rather than brown crumbly compost if this is not rectified.
   
   
4. Musky / Earthy Odour | Normal – compost ready
   
   Explained: This musky, soil-like smell is generated when the compost is mature and ready to use. This is what your final product should smell like.

Preventing Unwanted Odours

Not only are putrid odours unpleasant to the human nose, but they also run the risk of attracting unwanted flies and vermin. They are sensitive to the odours and use them as a means of detecting rotting food which they will try and get to using any means.

Will Turning the Compost Remove Odours?

No. In fact, turning will increase the odours given off during the process.