Dragon fruit, when it is ready and how to keep it.

Dragon fruit (kaeo mangkon) is harvested once the skin has turned almost fully red, and a University of Hawaii guide found that ethylene, the gas that ripens many fruits, does not start colour change in it. Whole fruit keeps about 14 days at 10 degrees Celsius. A fridge much colder than that can injure it.

What the skin shows

The Thai Department of Agricultural Extension (DOAE) describes dragon fruit as oval, 500 to 800 g, with pink skin and green sepals. The flesh is white, red or pink, and in every type it holds tiny black seeds. The taste is sweet.

The Hawaii extension guide gives more on the skin. The peel is red with large green scales, and the scales turn yellow as the fruit ripens. On the plant, skin colour starts to change 25 to 30 days after flowering. Flesh firmness is at its lowest, and eating quality at its highest, around 33 to 37 days after flowering.

Growers use "skin changed to almost full red" as their sign of maturity. Fruit can be harvested anywhere from 25 to 45 days after flowering, and the guide cites 32 to 35 days as the recommended window. It also notes that fruit harvested at 25 days is more sensitive to cold damage than fruit harvested at 30 to 35 days.

When it is in season

DOAE lists dragon fruit as available all year, with the peak from May to October. November comes just after that peak. The fruit is still easy to find, though the heaviest supply has passed.

Keeping a whole fruit

The guide recommends 10 degrees Celsius for storage and gives a life of about 14 days at that temperature. In one trial, fruit harvested 30 to 35 days after flowering lasted 17 days at 5 degrees Celsius and 90 percent relative humidity. But the guide warns that 5 degrees can cause chilling injury once the fruit is moved back to 20 degrees, and that 6 degrees can cause it too. It concludes that 10 degrees for a maximum of 14 days is the better recommendation. DOAE gives the same figure: 14 days at 10 degrees Celsius with 90 to 95 percent relative humidity.

Chilling injury shows in a few ways:

• the flesh turns translucent
• the fruit softens and wilts
• the scales darken
• the outer flesh browns
• the flavour is poor

These figures come from trade and research storage, not from kitchens. A household fridge is usually colder than 10 degrees, and neither source gives home advice. What the numbers do show is that whole dragon fruit does not like deep cold. Neither source states how long a fruit lasts at Thai room temperature, so that figure is left out here.

Cutting and keeping cut fruit

DOAE shows one way to cut it: halve the fruit lengthwise, cut each half in two, then slice the pieces lengthwise.

According to the Hawaii guide, cut dragon fruit is sold in overwrapped trays in South East Asian markets. In a trial it was stored at 4 degrees Celsius for 8 days. The guide calls that a potential, not a rule, and a trial tray is not the same as a bowl at home.

In short

• DOAE lists dragon fruit as available all year, peaking from May to October.
• The Hawaii guide uses skin turned almost fully red as the sign of maturity, and says ethylene does not start colour development.
• The guide recommends 10 degrees Celsius for up to 14 days. DOAE gives the same figure.
• Colder storage, 5 to 6 degrees, can cause chilling injury, with translucent flesh, softening and browning.
• Cut fruit was stored for 8 days at 4 degrees Celsius in one trial.

Sources

• Dragon Fruit, Postharvest Quality-Maintenance Guidelines (University of Hawaii, CTAHR, F_N-28)
• Dragon fruit (Department of Agricultural Extension, Thailand)