>How ice cream freezes

>This is in answer to Sebastian6’s question:

“Could you, at some point, please expand on the notion of whether a mixture will freeze or not? I was always under the impression that almost everything freezes except alcohol when you bring it below 32 degrees. Does cream have trouble freezing? Is it the sugar? When something doesn’t freeze what does it, in fact, do? Does it just take longer to freeze?”

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When you freeze ice cream this is what happens:

1) The water in the product (dairy, fruit, etc) freezes.

2) The ice cream machine whips AIR into the cream as the product freezes- like when you make whipped cream. This creates what is called the RISE– the ice cream will literally rise up out of the machine as it freezes. With my machine I know my ice cream is done when it literally rises out of the top of the plastic cover of the machine.

– The rise is important because it makes an airy creamy dessert. Otherwise you’ll just be eating at ice cube- like a popsicle. If you want to experience this try freezing some of your extra base without the machine. It tastes good, but the texture isn’t the same.

– The rise is doubly important because this is how commercial ice cream makers abuse the ice cream process. They whip tons of air into the product so that it’s very light; when you buy commercially made ice cream you are PAYING FOR AIR. If you lift a pint of commercial ice cream and a pint of my homemade ice cream mine tends to weigh at least 2x as much.

– David Leibovitz describes making ice cream without an ice cream maker by stirring the base as it freezes with a fork (every half hour or so). Or blasting it with a hand blender. Either way, you’ll seperate the ice crystals, but you won’t get nearly as much rise.

3) The SUGAR in the ice cream gets between the water molecules as they freeze into an icy structure. This keeps the product soft and pliable. Alcohol does exactly the same thing, but with more gusto.

Now think about what happens when you freeze a sugar solution such as honey or maple syrup. Some of the water in the solution might seperate and freeze, but since there is so much sugar suspended in the liquid you’re also going to be left with a sticky and very stiff but not entirely frozen substance. It would freeze at a colder temperature, but most home fridges don’t get cold enough.

So my honey ice cream had far too much sugar in it to allow the base to freeze. I actually ran it through the machine separately twice before I realized what was going on (I have to clean the bowl, allow it to dry completely, and then freeze it for 24hrs each time I want to use it). When I added the extra cup of cream I added enough water to the mix that the ice crystals were able to form around the sugar and the base froze properly. Hopefully my molasses ice cream won’t have this problem since I’m aware of the issue and was proactive in my avoidance of it.

I believe Alton Brown has an episode where this is demonstrated by slow dancing teenagers and overbearing chaperones.

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Posted on April 23, 2008, in Uncategorized. Bookmark the permalink. Leave a comment.

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