Oranges Turning Orange

Back in August I noted that the oranges trees that border our Montebello neighborhood had produced oranges, but that the oranges were still green. They stayed green for a very long time. Some time in October--I think it was just after the gota fría--we happened to see the farmer doing some work in the grove early one morning and asked him when the oranges would be ripe for harvest. "Mayo" (May), he said. That seemed improbable to me. After all, the oranges were already really large. But they were also still emerald green.

Now the first Sunday in December, the oranges have turned orange. It's been happening over the past couple weeks, and that prompted me to wonder how, and why, oranges turn orange. Is it similar to the way the leaves on the trees of New Hampshire turn yellow and orange and red in the fall? Do oranges also need warm, sunny days, but cool nights, to turn orange?

I've spent the better part of the afternoon searching on the Internet for information about why and how oranges turn orange, and it hasn't been as easy as I thought. Searching both in English and Spanish, I didn't find much about why they turn from green to orange. I did find a lot about how they can be made orange from green in a post-harvest process called "de-greening," or el desverdizado, so as to make the mature fruit more appealing to the consumer. It seems to be generally accepted both in Spain and in the U.S. to "de-green" oranges after they leave the tree.

But what was even more startling to learn was that oranges, if left on the tree, may actually revert to green after they have become orange. That would happen when the weather turns too warm, because it is cool temperatures that kill the green chlorophyll pigments and allow the yellow carotenoids beneath to show through. It starts getting warmer in May in Spain, so I'm thinking that perhaps the orange grove owner meant that by May his harvest of oranges would be done, because otherwise they would start turning green again. And though green oranges are mature, they are not appetizing to many consumers.

Today I feel doubly lucky. First, I'm lucky to live by an orange grove, and second, to see fruit that is actually orange, still on the tree, and not yet harvested. Now I'm watching to see when these fruits are actually harvested, and whether any turn green again before next May.