Ice Cream Mixture Suddenly Became VERY THICK While Heating. Help

I'm making ice cream, and while heating the mixture over the stove, it suddenly turned really thick before ever reaching a boil. What did I do wrong, and should I toss it?

The ingredients were added as follows:
Sugar and cornstarch were mixed together, then heavy cream, milk, and agave syrup were added to mixture. The heat was turned on to low medium and stirred slowly and constantly with a whisk. Tiny air bubbles appeared, likely from stirring. Suddenly, while mixture was warm but never bubbled, the whole thing because REALLY thick and paste-like...similar to the consistency of tooth paste. I tried to strain it, but it wouldn't go through the sieve. I put the whole thing into a bowl, covered it with wax paper, and put it in the fridge to consult the internetz.

My questions are:
Why didn't it ever bubble or boil?
Is adding the corn starch before the milk and cream an issue?
Should I lessen the amount of agave syrup used? (I substituted 1/4 cup agave syrup for 1/2 cup corn syrup) Should I add 1/2 cup milk to make up for the difference here?

The whole mixture was nice and thin...until it wasn't. What role does heating play in making the mixture? Is bringing it to a boil necessary?

  • Posted by: Nicole
  • April 29, 2019


Stephanie B. April 29, 2019
Sounds like your cornstarch kicked in with a vengeance. Have you used this recipe before? I'm new the world of homemade ice cream but I've only used cornstarch in recipes that didn't have as much egg and/or milk. In my experience with custards, pastry creams, and ice cream bases, they will start to thicken before they come to a visible boil. I don't think mixing the cornstarch with sugar is an issue, this is pretty common in custards to break up any clumps. I don't think the agave was a problem either. Did you do this in a bain marie or over direct heat? Hopefully someone with more ice cream experience can help.
Stephanie B. April 29, 2019
Oh I forgot to add: I don't think you risk anything but a little milk in trying to thin your base. It's not going to get thinner on its own. But a safer bet would be to just start over :/
Nicole April 29, 2019
I did it over direct heat. I'm thinking of substituting sugar for the corn starch AND the corn syrup. Is this ok?
Stephanie B. April 29, 2019
Try using a bain marie type set up, or something to keep your base off of direct heat. I like to put heat proof bowl over a pot of simmering water, and make sure my bowl doesn't actually touch the water. It takes longer to thicken, but it's safer. Does your recipe have egg? I didn't see it in your post. If you don't have eggs or cornstarch, I don't think your base will thicken so don't get rid of all the cornstarch! It sounds to me like your base thickened too quickly for you to catch when it was a good thickness. It happens, I scrambled the yolks last time I made a custard because the mix was too hot and thickened too fast. Feel free to post the recipe if you think it will help! I would compare it to other recipes I'm familiar with and see if its comparable.
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