As you open the lid you would expect a fermentation smell (similar to pickled vegetables or a spoiled apple). You shouldn’t have smells when it’s closed

It is very important to drain the juice from your composter every few days to avoid any stronger smells. The liquid is concentrated. The acids react with the air and can make a strong smell if left to fester. Also check your tap isn’t blocked, this can cause a liquid buildup and subsequent smell.

If your bucket has a decayed smell it may have spoiled – this is quite rare as the microbes added kills bad bacteria and prevents this. Black mould or a decayed smell is a sign of this, and is most likely due to neglect, no accelerator added, or spoiled food put in the bin. If this happens empty the bin, spray with some accelerator and bury. Make sure it is cleaned well with water and a small amount of detergent or vinegar. Don’t use harsh chemicals. Start your bin again, and make sure to follow instructions.