Never withered lettuce again: this is how you keep those leaves green and edible | Cooking & Eating

Lettuce is not the easiest vegetable to keep as long as possible. “If you bought lettuce and don’t want to eat it right away, wait to wash it,” says food scientist Nathalie Bernaert, fruit and vegetable researcher at ILVO, the Belgian Institute for Agricultural, Fisheries and Food Research. “There is a layer on the leaves that helps the plant to protect itself. The longer that layer remains on the lettuce, the better. Once the lettuce has been washed, it is best to dry it well if you still want to store it.”

Water is a source for micro-organisms, explains Bernaert. “The less water is available, the less well they can grow. That’s why people often say that lettuce is best stored in a plastic bag at the bottom of the fridge and with a piece of kitchen paper in it. That tip actually follows the same reasoning: the kitchen paper will absorb the moisture, so that no pool of water can form at the bottom of the bag. Such a puddle of water is a breeding ground for spoilage, just like drops on the edge of the bag.”

A head of lettuce or a bag of pre-packaged lettuce: which kind can we keep the longest? ,,At first glance, the pre-packaged lettuce will spoil the fastest, because it has already been cut”, thinks Bernaert. “When the lettuce is cut, enzymes are released from the cells of the vegetable. These will oxidize with oxygen, causing the lettuce to turn brown. However, the lettuce is usually in bags that are filled with nitrogen and CO2. As long as the bag remains closed, the lettuce will not be affected by the oxygen normally found in normal air. Once the bag is open, that advantage is gone and the lettuce spoils faster.”

Does it make sense to store the lettuce in a bag and inflate it yourself, so that no ordinary air enters, but CO2 from your breath does? “I doubt that,” says the nutritionist. “There are probably other bacteria in your breath. You don’t know what the effect will be on the lettuce. I think it’s a better idea to close the bag as soon as possible and to keep it as airtight as possible, so that as little oxygen as possible can get in.”

You can buy a classic head of lettuce with the root ball still attached. That is a bit more hassle in the kitchen, because the soil is still attached, but a clod can provide advantages compared to a ‘normal’ crop, Bernaert sees. ,,The fewer actions the lettuce undergoes, the better it can be stored. With lettuce that is still on a root ball, there is still no cutting surface through which the head can lose moisture. So you keep the plant active for a little longer.”

If you do have a crop with a cutting edge, then according to the nutrition expert there is a smart hack to get around that. ,,You can make a cross at the bottom of the crop and put it in a bowl of water in the fridge. This is a way to keep the crop fresher for longer. This way he can suck up fresh water and continue to feed his leaves. This can help keep lettuce for longer than a few days.”

All types of lettuce will stay freshest when they are kept cool. “A refrigerator temperature of about 4 degrees is ideal. Most fruits and vegetables store best at a slightly cooler temperature. This certainly applies to vegetables with a high moisture content, such as lettuce.”

And what if your lettuce is no longer so fresh? “If you have a large amount of lettuce that is no longer fresh enough for a salad, you can make soup from it to freeze. Freezing fresh lettuce leaves is not a good idea. During freezing, water crystals are formed that break the cells of the lettuce. When you thaw the lettuce afterwards, the water flows out of those broken cells. With lettuce you will then be left with a loose knit. You won’t have that problem with soup, because the cells have already been mixed to pieces.”