Ripening is the process by which fruits attain their perfect quality, desirable flavour (often linked with the intensity peak of sugar in the fruit), good colour as well as good textural proprieties. The ripening process is due to the conversion of starch to sugar in the fruit. Depending on the way this process takes place, the fruit can either continue to ripe after the harvest until it is eaten (or rotten), or stop ripening as soon as it is harvested. In the diversified world of fruits, we can yet classify them in 2 categories: climacteric and non-climacteric.

The difference between these 2 categories is based on one key component: a gas named ethylene also defined as the ripening hormone.

Climacteric fruits   

      Climacteric fruits produce ethylene along with the increase of their respiration. Those fruits are usually harvested green and unripe, in order to let them ripe during transportation and be at the best condition when reaching the final consumer.

One may control the ripening process under controlled conditions and temperature as the ethylene production of the fruit depends on the atmosphere surrounding it. Placing fruits in a modified atmosphere room (such as a cold room or a refrigerator) can keep them for a certain time at a similar degree of maturity or significantly decrease their maturing process. On the other hand, if one places ripe fruits generating a lot of ethylene close to unripe climacteric ones, they will reach maturity faster as they will start producing the hormone faster.

When this production starts, ethylene brings out the synthesis of different enzymes that will make changes in the fruit. Thanks to them, acids will be broken, giving a more neutral taste to the fruit and the starch will be metabolized, liberating sugar. The chlorophyll giving the characteristic green colour of an unripe fruit will be removed to give way to anthocyanins, pigments responsible for the yellow to red colouring of fruits (also known as powerful antioxidants). Under the action of ethylene, pectin – a molecule responsible for the hardness of a fruit -, will start breaking down.  The fruit will get softer and aromatic components will gradually form , releasing from the fruit a nice and delicate flavour.    

Non-climacteric fruits 

      Non-climacteric fruits produce a very small amount of ethylene as they don’t increase their respiration. They simply don’t ripen anymore after harvest. With this category of fruits, maturity when harvesting is the same as when consuming the fruit.

Ethylene treatment can occur on non-climacteric fruits, as a de-greening agent for their skin. The process breaks down chlorophyll pigments, responsible for the external green colouring of the fruit, and allows the yellow or orange carotenoid pigments to be expressed. For climacteric fruits, no treatment is needed as they naturally produce ethylene.     

NON EXHAUSTIVE CLASSIFICATION OF DIFFERENT FRUITS VARIETIES

Some useful tips to handle fruit maturity

Do not put climacteric fruit together if you want to keep your fruits longer, but gather them if you want them to ripen faster.

Wrap the crown of the bananas bunch. It will preserve them from degradation.

Putting bananas in the fridge will keep them fresh. Even if skin turns dark, they are still good inside! 

Grapes will absorb odours produced by leeks and green onions. Do not put them together.

Wash berries in a vinegar bath (1/3 vinegar, 2/3 water), gently rinse and dry in towels before storage.

Unripe kiwifruits are ethylene sensitive. Ripe kiwifruits are ethylene producers.

Pears are ripe when flesh around stem gives to gentle pressure.                  

Always refrigerate cut melon; cover well and store away from other products. Use cut melon within two days.

Only store fully or half-ripened papaya in the refrigerator since cool temperatures shut down the ripening process.

Pineapples and rhubarb absorb odours produced by avocados and green peppers. Keep them separated when storing.

Separate citrus from meat and meat-based products, as those latter absorb their odour.

To keep grapefruits and oranges longer, store them in perforated paper bags.

If you see that you won’t be able to eat all the fruits already ripe that you have, don’t throw them away! Other ways to preserve them exist:

• Freezing: peel and cut the fruit, place it in a reusable silicone bag and freeze. It will be ready to use once you need it (better use to cook, bake or in smoothies when you de-freeze it)

• Drying: cut the fruit in slices and put it in oven at low temperature for few hours. It needs a good ventilation to let the moisture evaporate (you can let the oven door partially open)

 Sources

Home storage guide for fresh fruits and vegetables. Available on : http://www.halfyourplate.ca/. Consulted the 05/12/2018

Infographic: See how to keep your produce from going bad too fast. Available on : https://fullplateliving.org/. Consulted the 05/12/2018

Tnau Agritech – Fruit ripening. Available on :  http://agritech.tnau.ac.in/. Consulted the 28/11/2018

Hamburg University – Fruit growth and ripening. Available on : http://www1.biologie.uni-hamburg.de/. Consulted the 28/11/2018. 

Quisqualis Rare fruit, tropical fruit and rare plant information – Climacteric and non-climacteric fruit list. Available on : http://www.quisqualis.com/Climacteric.html. Consulted the 28/11/2018