If you forage for wild greens, you probably already know how to blanch and freeze. It’s the best way to preserve your leafy harvest, maintaining both the color and nutrition of the plants you’ve picked. If you’re just starting out, this is a preservation technique you’ll use time and time again. And thanks to Harold McGee and his fantastic book On Food and Cooking, I can explain to you, dear reader, exactly why blanching and freezing is so important.
Freezing your leafy greens stops their metabolic processes. When the water in plant tissue freezes, it becomes immobile, and this, in turn, immobilizes most other molecules in the plant, causing MOST chemical activity to come to a screeching halt.
Notice how I capitalized MOST? Some chemical reactions are actually enhanced by freezing. The formation of ice crystals speeds up the enzymatic breakdown of both pigments and vitamins by concentrating the enzymes and other molecules responsible for these processes. As a result, your frozen food will thaw to be less beautiful and less nutritious than it was when it was fresh.
Here’s where the blanching comes in. To blanch your greens, bring a large pot of water to a rolling boil, and plunge your greens into the water. Leave them there for no longer than one – two minutes, then strain and transfer the greens to a bowl of ice water. Blanching stops the enzymatic breakdown of pigments and vitamins, and the ice water bath stops the cooking. Overcook your greens and you’ll be left with mush. Undercook, and your frozen greens will end up a dull color with fewer nutrients.
Once your greens have completely cooled, squeeze out as much water as possible from the leaves, to minimize the accumulation of ice crystals in the plant tissue. These sharp crystals puncture the plants’ cell walls and destroy the structure of the plant, once again leaving you with mush.
If you plan to freeze your greens long term (more than a few weeks), use a vacuum sealer to package them. Contact between cold, dry air and frozen foods can lead to freezer burn. Because water seeks equilibrium, and because the air in your freezer is very dry, ice crystals evaporate from frozen food into the air. This results in stale flavor and tough texture.
Remember how hard you worked to harvest your nettles, dock, mustard greens, and amaranth? Surely you don’t want all that effort to go to waste? The extra steps of blanching before freezing, then tightly packaging your greens and removing as much air as possible, is worth the time it takes to preserve your harvest at its peak.