Managing the ripening of fruit
The ripening of fruit is a high energy process set off by a biological trigger.
The trigger is the presence of acetylene gas. The higher the concentration, the faster the fruit will ripen. This principle is used by supermarkets to force-ripen fruit in response to consumer demand.
However, fruit ripened in this manner is grossly inferior. Recall that ripening is a high-energy process. Vine-ripened fruit are supplied with large quantities of sugars, antioxidants and nutrients in general by the plant. Force ripening of fruit in a warehouse produces only the appearance of ripeness; the flavour is bland and the fruit poor sustenance.
Fruit can also be force-ripened on the vine by enclosing the fruit – or the whole plant – and supplying acetylene to the enclosure. There are various ways to go about this. The primary domestic method is to put a bag over the fruit and place ripening bananas in the bag. This method has tremendous advantages for the home grower because it is possible to ripen fruit progressively rather than all at once. The bag also keeps pests off the fruit.
Ripening bananas emit a steady trickle of acetylene. The more bananas, the more acetylene. The larger your enclosure, the more acetylene you will need. For tent type enclosures over several plants, bottled acetylene may be used, especially when bananas are unavailable.
Acetylene from carbide
It is possible to make acetylene from calcium carbide. Place a small lump of carbide in a flat metal tray and arrange a drip feed of water onto the carbide. You control the rate of reaction by limiting the rate of supply of water. Do not drop a lump of carbide in a bucket of water to see what happens, it will react too fast generating heat and acetylene, which is the highly flammable gas used in a cutting torch. While a bucket full of water will absorb quite a lot of the heat making explosion unlikely, the large quantities of acetylene produced may be toxic.
When the carbide has been consumed there will be a paste of calcium hydroxide in water. This is a strong bleach, so take care disposing of it.