Sweet corn is a seasonal favorite, but its peak flavor and tenderness are fleeting, making precise harvest timing necessary for quality. The sweet flavor comes from a genetic mutation that causes the kernels to store sugar instead of rapidly converting it to starch, as occurs in field corn. The ideal time to pick sweet corn is known as the “milk stage,” which is the brief period when the kernels are fully formed and filled with a sweet, milky liquid. Harvesting at this stage ensures the highest sugar content and the most desirable texture.
General Timeframes for Ripening
Sweet corn varieties typically mature between 60 to 100 days after planting, but this varies based on the cultivar and local growing conditions. A more reliable initial marker is the appearance of silks, which are the fine, hair-like fibers emerging from the tip of the ear. Each strand of silk is connected to a single potential kernel and must be pollinated.
The ear is generally ready for harvest approximately 15 to 22 days after the silks first emerge. This timeframe is an estimate and can be accelerated by warm weather; for example, corn may only remain in prime condition for a day or two if daytime temperatures consistently exceed 86°F. Because corn development is sensitive to temperature and moisture, visually inspecting the ear is more dependable than counting days on a calendar.
External Visual Cues of Readiness
Before peeling back any husks, several external signs can gauge maturity. The husk should still be a vibrant green color, though it may lose its sheen as the kernels swell inside. The ear should feel firm and plump when gently squeezed, with the tip feeling rounded and filled out rather than tapered or pointed.
The most telling external indicator is the silk tassel emerging from the top of the ear. When the corn is ready, these silks should be completely dry, brown, or black, and brittle. If the silks are still yellow, green, or sticky, the pollination process is likely incomplete, and the kernels have not yet fully developed. A mature ear will also begin to angle slightly away from the main stalk.
Confirming Maturity with the Kernel Test
The definitive way to confirm the ideal “milk stage” for harvesting is to perform a kernel test. This involves gently peeling back a small section of the husk near the tip of the ear to create a “window” without fully shucking the ear. Once a few kernels are exposed, a fingernail or a sharp pin is used to puncture a kernel about a third of the way down the ear.
The liquid that emerges from the punctured kernel reveals the corn’s stage of maturity. The ideal result is a thin, milky-white liquid, which confirms the ear is at peak sugar content (the milk stage). If the liquid is clear and watery, the corn is underripe and needs a few more days to develop its sugars. Conversely, if the liquid is thick and paste-like, the kernels have passed the milk stage and have begun converting sugars into starch, resulting in a tougher, doughy texture.
The Importance of Timely Harvest
Harvesting sweet corn at the milk stage is important because the sugar content is at its maximum and declines rapidly thereafter. This decline happens because the harvested ear continues to respire, converting its stored sugars into starch. For standard sugary varieties, up to half of the sugar content can be lost within 24 hours if the corn is left unrefrigerated, affecting the flavor and tenderness.
The immediate conversion of sugars to starch is why sweet corn is noticeably sweeter when eaten immediately after picking compared to corn that has been stored. Picking too early results in kernels that are watery and lack flavor, while picking too late yields a starchy, tough product.