What makes fruit rippen?

Our fridge at home has two drawers at the bottom, one marked fruit, the other vegetables. I thought this was just decorative but it turns out there is a good reason for storing fruits and vegetables separately. Many fruits generate ethylene gas while they ripen; ethylene (C₂H₄) is odorless, colorless and natural. The refrigerator acts as a trap for ethylene gas which can lead to early spoilage of gas sensitive fruits and leafy veggies like lettuce.  By understanding this process you can force some items to ripen faster or prevent other items from spoiling quickly.

Ethylene's affect on fruit was discovered by accident when lemon growers learned that newly harvested green lemons ripened faster when kept warm in kerosene heaters sheds. But the lemons no longer turned yellow in time for shipping in new eclectically heated sheds. In 1959 researchers found that the secret ingredient was not the heat but ethylene gas emitted by the kerosene heaters.

The Ethylene-producing fruits include: (VH=very high, H = high, M = medium, L = low, VL = very low)

• Apples (VH)
• Apricots (H)
• Avocados (H)
• Bananas (M)
• Blueberries (L production, also L sensitivity)
• Cantaloupes (H)
• all Citrus (VH, except for grapefruit VL)
• Honeydew melons (M)
• Kiwis (L production but H sensitivity)
• Mangoes (M)
• Nectarines (H)
• Papayas (H)
• Peaches (H)
• Pears (H)
• Plums (M)

The Ethylene-sensitive fruits and vegetables are:

• All the fruit listed above, and...
• Asparagus
• Broccoli
• Brussels sprouts
• Cabbage
• Carrots
• Cauliflower
• Cucumbers
• Eggplant
• Green beans
• Lettuce, Kale and other greens
• Parsley
• Peas
• Peppers
• Potatoes 
• Spinach
• Summer squash
• Sweet potatoes and yams
• Watermelons

Note that the ethylene producing fruits are also ethylene sensitive. If you put bananas in a closed bag they will ripen faster as the gas builds up inside the bag.

Refrigerated fruits and vegetables should be kept in perforated plastic bags in different produce drawers of the refrigerator. You can either purchase perforated plastic bags or easily make your own by poking small holes in unperforated plastic bags (about 20 holes per medium-size bag).