How To Prevent Sliced Eggplant From Turning Black

Sliced eggplant that's started to discolor is safe to eat but it can look unsightly when it loses its fresh, creamy-colored appearance. This isn't much of a problem if you're planning on coating each slice in breadcrumbs and shallow frying them to make eggplant parmigiana because the brown spots are hidden from view. However, you may want to slow down the browning process if you're going to chargrill them for a salad, or simply want to chop them up early in advance of dinner to use in an array of eggplant recipes. Luckily there's a very easy way to prevent them from browning so quickly — submerging them in a solution of milk and water.

When eggplants are sliced, the cells inside their flesh are damaged and release an enzyme called polyphenol oxidase. When exposed to oxygen and the anthocyanin in the purple skin (the compound responsible for lending eggplants their characteristic hue), this enzyme causes the flesh to turn brown. 

To prevent your eggplant slices from turning black, mix a splash of milk into a bowl of water and submerge them in the liquid. This move reduces the eggplant's exposure to oxygen, helping it to retain its natural color for longer (water contains oxygen but much less than the levels in the air). And secondly, the milk proteins in the liquid coat the exterior of the slices and curb the small amount of oxygen that is in the water from getting to the flesh.

Using a larger proportion of milk helps to draw out some of the bitterness in the eggplant. Plus, the process of absorbing the milk elicits a creamier texture in the slices once cooked (don't worry about them falling apart as the skin provides structure to the rounds, helping them to stay intact as the flesh softens and becomes tender). You can also weigh them down with a plate to prevent them from bobbing out of the solution to encourage great absorption as well as cut them into uniform slices with a tool like this handheld mandoline.

If you're on a dairy-free diet, substitute the milk for a squeeze of lemon juice. The citric acid in the lemon hampers the enzymatic process by inhibiting the activity of the polyphenol oxidase, thereby helping to preserve the color of the eggplant for longer. Bear in mind that if your eggplant is wrinkly, has a squishy exterior, and has any brown spots on it that are immediately visible when you cut through its deep purple flesh, it may be on its way out. If you cook it at this point it may have a bitter taste and unpleasant texture so you might be better off discarding it or tossing it onto your compost heap.