Are hardware store themocouples food safe? I recently finished reading The Blue Bottle Craft of Coffee: Growing, Roasting, and Drinking, with Recipes. The authors of this book put a strong emphasis on accurate measurements and measuring tools, both for coffee and baking, and regularly make use of general purpose thermocouples as shown in the excerpt and picture below:

One of the greatest kitchen gadgets you can have is a thermocouple (shown below). A thermocouple is an electronic temperature sensor that can be purchased at the hardware store, and is typically used in science and industry for testing the temperature of ovens and air conditioning. They’re fairly inexpensive, absolutely accurate, and very easy to use and clean. I use mine for verifying my oven temperature and for taking temperature readings on sugar syrups and other temperature-sensitive recipes, such as Homemade Yogurt. It’s an invaluable and extremely accurate tool that is worth investing in for both baking and coffee preparation.


I can see the appeal of these &quot;hardware store&quot; thermocouples, but are they really safe to use in and around food or drinks? None of them claim to be suitable for cooking. Is there a likelihood that they could leave behind undesirable chemicals or metals?
You are correct to be concerned.

In all likelihood, the hardware store thermocouple is not suitable for food use as it would contain metals you don't want to ingest. Here is a table of industrial grade thermocouple materials, note presence of some undesirable metals:



Source.

You would want a thermocouple specifically made for food use. Example. I found that one by searching NSF thermocouple, a cautious approach since NSF (National Sanitation Foundation) certification entails high standards. But most thermocouple advertised for food should suffice, such as this $16 one.