If you've been waiting for your avocado fruit to ripen on the tree, you may be in for a long wait. For, like bananas and kiwi fruit, avocados are climacteric - which means they mature on the tree but ripen only when picked. This might explain why your avocado fruit always seems so hard.

Yet most avocados can take between 6-18 months to mature - depending on the variety - and only when they appear to take on a mature size and shape are they ready to be picked.

So, obviously the best way to ripen avocados is to pick them. However, how many times have you had an avocado sitting on your bench and three weeks later it still feels as hard as the day you bought or picked it? For me, it's been a few.

To understand how best to ripen avocados it is worth understanding the process that occurs in order for them to ripen. As a climacteric fruit, avocados dispel a chemical called ethylene as they ripen. (Supermarkets often use a synthetic ethylene to speed up the process - but you probably won't have this available). The ethylene builds up as the process continues until the fruit actually ripens.

Therefore, if you were to put them in a container or paper bag you would retain the ethylene build up and the ripening process would occur much quicker. Put them in the fridge and the process stops - which is helpful to know if you're trying to stop them over-ripening. Even putting other climacteric fruit alongside them will hasten the process.

Yet leaving them on a bench in a vast and airy room will ensure that they won't ripen any time soon.