The Science of Cryo-Blanching

At this time of the year, I imagine your freezer is full of excellent veggies frozen during summer for using them when required. So, you already know that, generally speaking, when you cook them you will be reminded of all the bright colours and flavours of summer, even though the consistency will be rather disappointing.

I can explain this better with an example: green beans that have just been thawed look inviting enough but if you touch them, they feel limp. If you toss them in the pan they will taste better, but nothing like the results obtainable from a fresh product.

What is cryo-blanching?

For this reason, the two chefs Alex Talbot and AKi Kamozawa have perfected a freezing technique called cryo-blanching which is based on a principle particularly dear to science: extreme cold has more or less the same effects on organic substances as extreme heat.

In cooking, however, there is a substantial difference. When we “sear” food, we rapidly take it to a high temperature but the freezing process takes much longer. This is the crux of the matter. Basically, freezing leads to the formation of ice crystals that break down the cell walls of vegetables, making them soft. If this process is slow, the crystals that form are very large and actually “rupture” the walls.

For this reason, we need to aim at a very rapid freezing process, which allows for the formation of small sharp ice crystals which merely puncture the cells walls, weakening them sufficiently to make our vegetables soft, but leaving them with a pleasing consistency. Then, when we go to cook them equally rapidly, the resulting vegetables will be brightly coloured and tasty.

Frozen green beans, peas and spinach.

The rules of cryo-blanching

In the cryo-blanching technique, freezing is all important. So, it is worthwhile learning how to do it properly.

1. Freeze in small quantities. If we pack a large quantity of our delicious dwarf beans, to quote the example above, they will take a long time to freeze, especially those in the centre of the “bundle” we have thrown into the freezer. To avoid this, it is preferable to arrange them in a single layer, neatly arranged. Don’t worry about how much space you take up: the volume is the same and if you do it in an orderly fashion you will actually save space. Besides, this tip also explains why the “family-size bags” of industrially frozen vegetables never come up to expectations. You are better off freezing them yourself!

2. Always use vegetables with a small cross-section. The larger they are, the longer they will take to freeze and this would take us back to square one. For this reason, the best vegetables to use for cryo-blanching are green beans, asparagus, peas and spinach. Once your vegetables are perfectly frozen, five or six hours later to be on the safe side, remove and repack them in a zipper-lock freezer bag, squeeze out any excess air and seal, before returning them to the freezer. You can store them like this for several months.

3. When the time comes to use your vegetables, cook them directly from frozen. The rapid transition from a low to a high temperature preserves most of their original flavour and aroma. Do remember, however, to use a very high temperature so that the water they expel evaporates quickly and prevents the product from overboiling.

Vegetables cooked in this way can be used in your favourite recipes but you may even dare to serve them just as they are, as if fresh. If not for the fact that fresh beans are not easy to come by in the middle of winter, it would be hard to tell the difference.

By FDL