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So I heat and whisk some cream with egg yolks, sugar, and lemon juice in a water bath until thick, whip the rest of the cream, mix the two together and put it into a freezer. After five or so hours I take it out of the freezer and it's done. It's the recipe from my ice cream book. Four yolks per 500 ml of heavy cream (33%). But it's not smooth, it has that "ice crunch". I can feel and hear those tiny ice crystals being crushed by my teeth (it's quite subtle, but it's there). How do you prevent ice crystals from developing in your ice cream?

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Fat must be the key, but I had plenty of it. Besides, you get no ice crystals if you just freeze whipped egg whites with sugar even though it contains approximately zero fat

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  • Are you churning it while it freezes?
    – Ecnerwal
    Aug 20, 2022 at 0:08
  • @Ecnerwal how do you imagine it? Aug 20, 2022 at 0:15
  • I think this is a no-churn ice cream.
    – FuzzyChef
    Aug 20, 2022 at 0:26
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    I noted that you didn't mention churning. But you didn't mention not churning, so I imagined that you might clarify what you were doing to make your question more clear. Evidently you prefer to be mysterious about it instead. Churning (or even hand-mixing from time to time as it freezes) would help to reduce the size of the ice crystals.
    – Ecnerwal
    Aug 20, 2022 at 0:35
  • @Ecnerwal I just tried to hand-mix it every half an hour for six hours. It was pain, and it didn't resolve the problem, unfortunately 🤷‍♂️ Aug 25, 2022 at 22:58

2 Answers 2

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The key points of avoiding the formation of ice crystals are primarily dependent to the speed of the freezing and the amount of agitation. Commercial batch freezers have more powerful compressors that only take 12-15 minutes to complete the process, while ice cream machines for home use tend to take 45-60 minutes. Also a higher dasher speed, with up to 200 rpm, can help to gain smaller ice crystals, but also results in a higher overrun, which might or might not be wanted.

A detailed description of the freezing process can be found in the Ice Cream Technology e-Book by H. Douglas Goff:

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  • Why don't any crystals develop in whipped egg whites? Aug 20, 2022 at 11:13
  • Also, what my practical takeaway should be? I don't have an ice cream machine, let alone a commercial freezer Aug 20, 2022 at 11:24
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    An ice cream machine, or liquid nitrogen, is required for smooth creamy ice cream. If you don’t have an ice cream machine, you’ll need to alter your objectives. Try granita, or semifreddo.
    – Sneftel
    Aug 20, 2022 at 13:48
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    Whipped egg whites contain a much higher amount of air than ice cream, meaning the contained water is distributed in small amounts around the trapped air, so no large ice crystals can form. To avoid the risk of salmonella I strongly advise against the usage of egg whites in ice cream.
    – J. Mueller
    Aug 21, 2022 at 12:08
  • Can I just hand-mix it from time to time, as Ecnerwal suggested in the comments? Aug 21, 2022 at 21:32
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For home use you are probably best off with a different type of ice cream.

There are quite a few no-churn recipes based on condensed milk and/or dulce de lecce (basically boiled, caramelized condensed milk) mixed with cream. I did it at home using just a normal household freezer and while not 100% classical Italian ice cream it is astonishingly good.

As for the "How to prevent" part:

I did quite often hear using sugar syrup and/or inverted sugar syrup. The idea is to reduce the probability of having crystallization kernels in the mixture.

Also adding a splash of alcohol is recommended, but I did not find any kind of official reference for that.

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