I posted recently a brief article on the pollination of sweetcorn. Naturally, the next question is how to tell when the cobs are ready to harvest? The first sign to look for is the silks – the bundle of fine threads at the end of the cob – turning brown and beginning to shrivel. With a little experience, one should be able to see, and feel, whether the cob has filled out with plump kernels. However, there is no need for guesswork, as there is quite a good way to test for ripeness.
Peel back the outer husk from the end of the cob. If the kernels are not plump, wrap it back up and leave for a few more days. Sometimes a cob will not be completely filled with kernels; poor pollination is the most probable cause, which is especially likely during dull or wet weather. There is no reason, though, not to still enjoy a partially pollinated cob.
Assuming that the kernels are plump, pull the husk apart and press a nail into a kernel a couple of inches from the end, and observe the juice. If it runs clear, it is not yet ripe; wrap it back up and wait a couple of days. If it is milky yet translucent, it is perfectly ripe. If it is starchy or there is no juice, it is past its best. It may still be passable, but with the natural sugars turning to starch, it will be nothing like the sweet and succulent experience of a just ripe cob. When older still the kernels will begin to shrivel, at which point it really is too far gone.
The old open pollinated varieties of sweetcorn are hard to find; few seed merchants stock anything but hybrids. With these old sorts, the conversion of sugars to starch happened very quickly, and it was important to get the corn from plot to pot as soon as possible for the best experience, being best consumed within as little as half an hour. Despite this, some maintain that the flavour is better than the modern hybrid varieties, sometimes referred to as supersweet or tendersweet depending on their genetics, that have been bred to include specific genes that reduce the amount of starch and increase the level of sugars, giving a much longer shelf life.
Despite my distinct preference for old varieties, we have so far grown only a modern variety, Lark, and admittedly the results have been very good. Next year, though, I am hoping to get hold of some seed of Golden Bantam, one of the few heritage varieties that can still be acquired. It will be interesting to see how it compares with a modern variety. Regardless of the variety, however, the quality of a freshly harvested cob cannot be beaten.