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I found a recipe for a No-churn rum and raisin ice cream.
In the recipe the first step is to put the raisins and rum in a saucepan and gently heat until boiling, transfer to a bowl, cover and leave to soak overnight.
I'm having trouble understand the need for boiling the mixture.

Why boil the rum and the raisins before leaving them to soak?
Wouldn't it be better to leave them to soak for a longer period of time?
Is this to speed-up the process?
Or is it to remove the alcohol?
Will the alcohol prevent the ice cream from freezing properly or give an undesirable structure/texture to the ice cream?

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I see a couple of reasons for bringing the small amount of rum and the raisins to a boil. First, this process will plump the raisins fairly quickly. Secondly, much of the alcohol will evaporate. Alcohol freezes at a much lower temperature than water. So, alcohol additions to ice cream make the final product softer. In this case, it would seem that given the no-churn technique, a little alcohol would be beneficial. So, you could leave them to soak without boiling, but it would take longer for your raisins to plump. So, alcohol will change the final texture, but you might like the result. It is possible to add too much alcohol. Max Falkowitz of Serious Eats writes that adding more than 5-6 tablespoons in a quart of ice cream base would result in an ice cream that doesn't freeze enough to be scoopable. If you eliminate the boil step, you will want to make sure you don't over do it with the amount of rum.

  • This is one of the few times you actually do boil off a significant amount of alcohol - because you evaporate a significant amount of rum before diluting it. Alcohol doesn't evaporate all that much faster than water so simmering an already dilute mixture isn't very effective. Here you concentrate the flavour as well. You could probably skip the boiling by using a mixture of rum and rum essence – Chris H Jul 28 at 11:50
  • @ChrisH the recipe states to gently heat until just boiling, then remove from heat. So, nothing is simmered. It appears that this is to avoid losing a significant amount of liquid/rum in the recipe...and alcohol evaporates at a MUCH faster rate than water because it has a boiling point of 82 C as opposed to the 100C of water. So, the alcohol will be drastically reduced in the time between 82C and boiling. – moscafj Jul 28 at 12:05
  • If you look into vapour pressures and boiling points of mixtures, which you need to, the rate of evaporation isn't that much greater. It's a common misconception that we've discussed before so I won't go into detail here. Heating gently until just boiling is quite similar to reducing gently - when you can see it steaming, you're getting rid of water and alcohol. 50ml of liquid is a very thin layer in even a small pan, with lots of surface area to evaporate – Chris H Jul 28 at 12:13
  • I guess I'll have to experiment with it this week. Make 2 batches, one with the heated/boiled mixture and one with a long soak and then compare :) If no-one comes up with an alternative explanation in the next couple of days I'll accept your answer. – yetanothercoder Jul 29 at 9:18

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