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I will be vending a soft serve/gelato at events and festivals this summer. I need to maintain its soft frozen temperature between 10 and 18 °F (-12 to -7 °C), but most events are very limited on power. I would like to use a cooling bath that needs to be safe around food.

32° is easy (ice) and 0° is easy (ice and salt). Should I just add water to the ice and salt mixture creating a slurry that would be a less efficient system? How difficult would it be to maintain a semi stable temperature? Are there other cooling bath mixtures you would recommend? I've done some research and found many of the alternatives are not food safe.

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    In a chemistry lab, ice-salt would make the most sense. You can vary the amount of salt you add, and that gives you a degree of control over the temperature. There are lots of possibilities for cooling baths (see: https://chemistry.stackexchange.com/a/44519/16683) but as you have found out, nearly all of them are not stuff you want anywhere near food. Have you considered asking this on [cooking.SE]? I can migrate it over there if you feel you would get better answers there - let me know. – orthocresol Apr 14 '17 at 18:59
  • Migrating it would be amazing. Any and all advice and information would be very helpful. I tend to think scientifically, but I haven't taken chemistry in over 20 years. So... I am doing research online and learning a lot, but it is slow going because I have so much to learn. Haha. Any help pointing me in the right direction is greatly appreciated. –  Apr 14 '17 at 20:04

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You could experiment with salt to ice ratio. Somewhere around 15% salt to ice ratio you get freezing in 10-18° F range.

Once you are at 10-18° F, you should have extremely good insulation to keep the temperature stable, have a thermometer placed very close to your gelato and constantly check that, have lots of frozen ice+salt mixture and minimized the exposure of your frozen content to ambient environment.