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Both slow cooking and pressure cooking are thought to be healthier cooking methods and they are certainly convenient but are the materials used in the appliances safe?


Why I Prefer Pressure Cookers to Slow Cookers


There is no perfect pressure cooker or slow cooker and there are issues with the materials in each type.  The concern with cookware materials is that heavy metals, synthetic chemicals, and contaminants can leach into food. Leaching increases with acidic foods, higher temperatures and longer cooking times.  I prefer pressure cookers because of their short cooking time.  The longer cooking times associated with the slow cooking method will increase leaching of any heavy metals or contaminants in the cookware.


Additionally, most new pressure cookers are made of stainless steel, which I consider a safe cookware material unless you are sensitive to nickel or chromium.  Make sure that the steel does not have a non-stick coating.  Some pressure cookers are made of aluminum which I don’t recommend.  You can read more in the Ultimate Guide to Non-Toxic Cookware about stainless steel, aluminum and non-stick coatings.


There is one caveat.  I don’t recommend using a stainless steel pressure cooker every day or with high frequency.  While stainless steel is one of the safer cooking materials, it does leach nickel and chromium.  You can read more about the health effects here.  I recommend using stainless steel cookware in a rotation of other safe cookware.


Are Slow Cooker Materials Safe?


I don’t recommend any slow cooker for regular use but some are better than others.


Glazed Ceramic

Most of you are probably aware of the danger of lead leaching from ceramic slow cookers.  This became widely publicized after a 2004 investigation by KUTV Salt Lake City found 20% of slow cookers leached measurable levels of lead.  Lead had been used as an ingredient in the glaze to improve shine.  Many manufactures have since stopped adding lead as an ingredient but it may still be present as a raw material contaminate.  Additionally, glazes can contain additives such as titanium dioxide to make white interiors and aluminum oxide to stiffen glazes.  The FDA randomly tests ceramic cookware for lead and cadmium but doesn’t test for other additives.  Additionally, the FDA limit for lead in large ceramic containers like slow cookers is 1 mcg/mL . There is no safe level for lead so it’s important to reduce exposures as much as possible. California Proposition 65 has a much more stringent limit for lead at 0.5mcg/day.  If you have a product that meets or exceeds Prop 65, it’s a better choice than one that does not.  But, due to the long cooking time that could increase the leaching of any contaminants I recommend avoiding this type of slow cooker.


Non-Stick Ceramic Coating

I don’t recommend non-stick ceramic coating for any type of cookware or appliance.  You can read more about it in the Ultimate Guide to Non-Stick Cookware.


Unglazed Ceramic

VitaClay and Miriam’s earthen cookware are two brands that make slow cookers with natural, unglazed clay.  There are no heavy metals added to the clay but because it is a natural material and there is no coating to protect against leaching, any contaminants in the clay could migrate into food.  Both VitaClay and Miriam’s provide testing that shows they meet or exceed California Proposition 65 standards for lead.  Miriam’s earthen cookware website lists one test performed by an independent lab that shows no extractable lead, extractable cadmium or arsenic.  That’s reassuring however, it doesn’t explain the testing method and because it is just one test, it doesn’t show consistent results with different batches of clay.  VitaClay provides one test performed with an acidic solution to accelerate leaching that shows no detectable levels of lead, cadmium, mercury and arsenic.


If you currently own one of these, I’m not suggesting that you don’t use it.  There is no evidence that there are harmful substances leaching from these appliances and people have cooked in earthenware for centuries. They may be fine to use but they are not without risk.


Stainless Steel

Stainless steel slow cookers are more of a concern than stainless steel pressure cookers because of the long cooking times, which increases leaching.  If you only plan to use a slow cooker occasionally, stainless steel slow cookers are fine but I don’t recommend them for regular use.


My Choice is an Instant Pot multicooker

For many years I used a VitaClay slow cooker but when it broke, I replaced it with an Instant Pot that has both pressure cooker and slow cooker functions.  I use the pressure cooker a couple of times a month and I use the slow cooker function only on occasion.  I don’t use it for highly acidic foods such as chili or tomato sauce.  I cook those in my glass ceramic Visions Dutch Oven.


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