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Cutting a chiffonade (that's super-thin ribbons) of leafy herbs is a nice way to get their flavor evenly distributed around the dish. It's pretty too. The only problem is that a lot of these herbs like mint, certain types of basil, and sage have a thick stem running through the center of each leaf, which can lead to tough, stringy bits in your food. It's best to remove these.
The fastest way to do it is to stack the leaves a few at a time, fold them over to secure them, then chiffonade them from one side, stopping just short of the central stem. Flip the leaves over and repeat on the other side. You should be left with just the central stem, which you can then discard.
Watch the video for more details.
Shopping and Storage
As with all herbs, look for bright, firm leaves and stems that stand to attention. There should be no browning. A little dirt on the leaves is ok, and you should always wash your picked herbs and spin them in a salad spinner before using to get rid of any dirt or sand that might be clinging to them. Nobody likes sand in their pasta or julep.
For relatively short term storage, store the herbs in a loosely closed plastic bag in the vegetable crisper. It should last at least four to five days. For longer term storage, you've got two options. You can either pick the leaves, rinse them, dry them, then roll them up in a damp paper towel placed inside a zipper-lock bag, or store the whole bunch with the stems in a glass of water. Place an opened plastic bag over the top of the cup. Either way, the herbs should remain fresh for at least a week.