The white pith just under the skins of citrus fruit is high in pectin. Any citrus fruit can be used, but choose ones that have a thick layer of white pith for good results with this recipe.

But to food scientist, Yang Shan, it is much more: the discarded pith, pips, skin and membranes of oranges and other citrus fruits are untapped reservoirs of useful compounds. “Our goal is to ...