(Updated, 3/15/17: new chart)
For the last few months, I have been weighing oranges before and after peeling to see what fraction of the orange is edible (by weight). I had done similar work previously to measure the edible percentage of avocados, finding that Haas avocados are roughly 70% edible by weight across a span of 125 to 300 grams, and was curious about oranges. Would there be a relationship between the initial weight and the amount that is edible? Or is finding a ‘high value’ orange an exercise in chance?
To get the edible part of the orange, I use a knife to cut off the peel and most of the pith (illustrated in photos above), then trim out any large pithy or peel-y parts at the core of the orange. The edible fraction is the ratio of the weight of the peeled orange to the weight of the unpeeled orange. Over the last few months, I weighed 23 navel oranges, 4 blood oranges (Moro, I think), 4 Cara-Cara oranges and 2 navel oranges that were labeled “XL” at Berkeley Bowl [update 1, 2/22/13: all of the oranges were grown in California]. The oranges came from several vendors at the Farmers Market and Berkeley Bowl. It’s not a definitive sample, to be sure, but good enough to make some basic (and not very surprising) conclusions.
The figure below shows the results, with the edible fraction (by weight) plotted against the unpeeled weight. The results are all over the place, so the unpeeled weight is not a good metric for finding value in oranges.
The results in the chart above are not too surprising: the edible fraction is determined strongly by the amount of peel, which is mainly a function of the diameter of the orange and peel thickness (i.e., edible volume = whole orange volume – peel volume), and the variations in the levels of sugar, water and membrane inside of the orange can cause two oranges with the same volume to have different weights.
Thinking about these measurements as I drafted the post, I realized that I should have also recorded the volume of the oranges so I could check for a correlation between volume and edible fraction. In addition, the right metrics for ‘orange value’ are probably not the edible fraction, but number of calories, quality of flavor or vitamin C content, items that I’m not equipped to measure (When all you have is a hammer…).
Were Discounted Tiny Oranges a Good Deal?
[update 1, 3/15/17] Berkeley Bowl had two-pound bags of tiny organic blood oranges on special for $0.70 per pound, a big discount from the usual $2 per pound for organic blood oranges. These oranges were tiny — much smaller than an average navel orange — as the photo to the right illustrates. I weighed some of the tiny blood oranges before and after peeling, and included the results in the chart above. With edible fractions of 0.65-0.7, they are at the upper end of the range, so they turned out to be a great deal — they weren’t all peel and pith.
I've also been told that peel thickness is a factor of how much water the tree receives. Years ago, when Florida had more oranges, the difference between Florida and California oranges was peel thickness. Florida oranges had slightly thicker… the orange layer?, and the white pith was very thin. California oranges had a thick white pith. Unfortunately, that has changed with droughts in Florida and the loss of many orange grove.
We used to have a couple of demi-wild orange trees by the roadside nearby. We ate from them two years, and on the dryer summer, the peel was thick and tough. (One of the fun things about the older Florida parks and [ever-rarer] undeveloped areas is that you can randomly stumble on an orange or grapefruit tree in the middle of the woods.)
Lastly.. OH MY GAWD! Blood oranges!!!!
Sorry, I just had to throw that in. That is one of the few things I eagerly await coming in season at our local overpriced "green" supermarket.