Recently in the United States, we celebrated Thanksgiving which marks the beginning of the season where many people are cooking larger and more specialized meals. Some people roast turkeys, some people prepare large servings in trays for their family gatherings. Oftentimes we check roasting meats using electronic temperature sensors or we cut and portion some of the food on plastic cutting boards, and the thought crosses the mind, are these materials food safe? Thankfully, manufacturers and distributors of cooking products carefully choose materials that are optimized for use with food meant for consumption. Let’s explore options in food-safe technology.
Contamination
Cutting boards are pretty basic in purpose but the material choice is very important. The desired behavior is multifaceted. You want a material that will not flake off or leach out, contaminating the food being prepared, and you want the material to not be damaged by the food itself. While many foods don’t seem very damaging to our skin, something as simple as warm salted water can slowly eat away at a stainless steel vessel if it’s not quite the right kind of steel. Because of this, you don’t want to just use any old FR4 panel. Materials that make contact with food can be made using materials like silicone, polyethylene, and PVC. Materials must be purpose chosen because different materials have different thermal and chemical resistance properties. For example, polypropylene is more often used for hot-water applications because the material is stable at hot water temperatures. Fortunately, the FDA keeps track of materials that are generally recognized as safe (GRAS).
Resilience
Whether cooking a turkey or a ham, thick meats often require their temperature to be monitored to ensure the food is adequately cooked. If preheating a pan for searing, contact-based temperature sensors are not great because the reaction time of contact sensors can be too slow to show the accurate surface temperature of a pan and if the pan is non-stick, you want to avoid contacting that surface with any hard metallic material. For this context, an infrared thermometer is great because the reading is very fast, and because it measures temperature without making physical contact, there’s no food safety worry at all. However, IR thermometers can only tell you the surface temperature of things. If you want to check the internal temperature, there’s no going around needing some kind of contact sensor. A wide variety of types of contact temperature sensors exist, but cooking would mainly be concerned with liquid water temperatures, so devices like thermocouples or RTD’s rated for high temperatures up to 500C are overboard. Instead, more common devices like thermistors can be used but are not food safe themselves. The temperature sensor can be inserted into a food-safe vessel and then thermally coupled with the food-safe material ensuring the only material touching food is food safe and ensuring the sensor temperature matches the surrounding material temperature. Often this encasing around a thermometer is steel, but not just any steel will do. Lots of cooking contexts involve contact with salted liquid that can also be acidic to a degree, creating a situation that would corrode some steels. For this, particular grades of steel like steel 316 which is an alloy that contains extra elements like chromium and nickel to give it higher acid, alkali, and chloride resistance allowing it to endure salt exposure without damage. This is great because we prefer to make gravy out of turkey juices instead of cleaning it off of the bottom of our oven.
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