Granny Smith apples peel powder

I am currently working on a dessert, as I see it in my mind it has a bright green apple skin dust covering it. I have tried to freeze dry the skins with dry ice using a method I found online with no luck. Is there a good way to accomplish what I am looking for without breaking the bank?

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Brandon_Byrd_40557

That's an application for liquid nitrogen if ever I've seen one. Check out the garnish for ChefSteps' aerated green apple sorbet which uses LN to make a granny smith apple powder.

FrankM_3301

My first thought too. That's the only way I can imagine to keep the bright green color...but it is probably a freeze and serve immediately situation.

dancurren

Sprinkle some citric acid or, better yet, ascorbic acid on the peels and freeze them. If you have a vaccum sealer, freeze them under vaccum until ready to serve.

There are colorless polyphenols in apples, and there is polyphenol oxidase in apples. These two molecules are normally kept apart, but when you slice into an apple, you break open cell walls, and allow the two to mix and react (which causes the browning).

The polyphenol oxidase enzyme only works in a limited range of acidity. Making the juice on the apple slice too acidic or too basic will prevent the enzyme from performing its function. A little citric acid sprinkled on the cut will do the trick.

Enzymes work more slowly, or not at all, when the temperature is reduced. Refrigeration or freezing will slow or prevent browning.

Like most enzymes, polyphenol oxidase needs water in order to work. Dehydration will prevent browning. However, dehydration takes time, and the browning reaction is quick, so while the dehydration is happening, we can use yet another trick, and simply prevent oxygen from the air from getting to the cut fruit. We could also freeze-dry the apple slices.

We could denature the enzyme with X-rays (irradiation) or electron beams. High pressure can also denature the enzyme.

Or we could remove the oxygen by using a more powerful reducing agent than the polyphenols. Ascorbic acid (Vitamin C) can be sprinkled on the cut fruit. It will combine with the oxygen and make it unavailable to the enzyme. It can also make the juice more acidic at the same time, so it has a double action. And, of course, you have just improved the nutrition of the fruit by adding a vitamin.

Other reducing agents used are sulfites, which are often added to cut fruit before drying in the sun.