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‘A ripe tomato produces enough Ethylene to stimulate the ripening process in another 48 fruits’

T.Watson- Unit 0A04, Plant Physiology, Semester 4, 1997.

A couple of weeks ago, I found myself talking about the process of fruit ripening to my colleagues during a coffee break (I am not sure how I managed to get onto the topic, but it ended up being quite a technical conversation). I studied this subject during my student years and it is something that has fascinated me since. Science geek I know, but I think it is worth sharing.

The process of fruit ripening is a topic touched on in the third unit of the Higher Biology syllabus. Fruit will ripen if there is a common ripening signal present. This signal is the production of Ethylene. Ethylene is a simple hydrocarbon gas (H₂C=CH₂ for the Chemists amongst you) that a ripening fruit will make. This signal causes the fruit to produce enzymes (hence the process is also temperature dependent and why most fruits are seasonal). These help to break down chemicals inside the fruit making it ripe. The degradation of starch by amylase to produce sugar is an example of one of these reactions.

If you think of this process in strawberries, the Ethylene signal causes the fruit to change from green to ‘fire’ red, hard to soft and bitter/sour to sweet. Ethylene is not specific. The gas produced by one type of fruit will stimulate the ripening process to start in another. I grew up on a farm where a large part of our business was the production of strawberries and raspberries. My Father and I always noticed that the drills of the later variety (that were situated beside the earlier variety) would ripen earlier than the rest of the crop. And this is why- the production of Ethylene by the earlier variety!

Today fruit is stored in cold temperatures. The air in warehouses is cycled through charcoal filters to absorb any Ethylene being made. This is why we can enjoy fruit such as apples all year round.

Just another random factoid!