Stainless Steel

Widely regarded as safe for food contact, and the migration research supports that with one honest asterisk. The metals that can come out are nickel and chromium, and the trigger is acidity plus contact time. Kamerud et al. (2013) held tomato sauce at 85 C and measured nickel and chromium rising up to 26-fold and 7-fold after six hours - but the same study found release dropped roughly tenfold between the first and sixth cooking cycle and then stopped changing, so a brand-new pan is the worst case and a broken-in one is not. Guarneri et al. (2017) varied pH directly and found release higher with unused pots and at low pH, concluding stainless pots are safe for the majority of nickel- and chromium-allergic subjects. Accominotti et al. (1998) cooked ordinary menus in glass versus stainless and found the stainless contribution very low next to the nickel and chromium already present in the food. The Council of Europe technical guide on metals in food contact sets a specific release limit for nickel of 0.14 mg/kg of food, explicitly derived from data on nickel-sensitised people. That group is the genuine exception: nickel is the most commonly patch-tested contact allergen, with a female predominance, though clinical guidance for sensitised people targets high-nickel foods (cocoa, nuts, oats, legumes) rather than cookware.

Heat by itself is a non-issue. Stainless does not soften, off-gas or shed anything at boiling, in a dishwasher, in an oven or in a hot car, and the leaching studies above never tested plain hot water - they tested acid, because acid and time are what move metal, not temperature. The real heat problem with 304 is the opposite of leaching: it conducts well, so an uninsulated handle, rim or lid knob gets hot to touch, which is exactly why so many otherwise all-metal products reintroduce a plastic or silicone part right there.

18/8, SUS304, A2 and EN 1.4301 all name the same alloy, so a spec sheet carrying any of them is telling you the same thing. Treat 18/10 with mild caution: consumer sources map it to 304, but a peer-reviewed paper (Guarneri 2017) titles its pots 18/10 (grade 316), so the ratio notation is commercial shorthand rather than a specification. A magnet is not a reliable test either - annealed 304 is effectively non-magnetic, but cold work forms deformation-induced martensite, which Carpenter Technology describes as leaving 302 and 304 weakly ferromagnetic when heavily cold worked, so a deep-drawn bottle body or pot base can pull on a magnet and still be 304. If a brand says only stainless steel, ask for the grade in writing; see Stainless Steel (grade unspecified) for what to do when they will not answer.

Dishwasher safe and effectively unbreakable in kitchen use. What damages it is chloride pitting - salt left sitting, bleach, prolonged seawater - and abrasive scouring that dulls the passive surface. Tea-staining and rainbow heat tint are cosmetic, not corrosion. The one routine habit that pushes a vessel into the acid-plus-time regime those studies measured is descaling with undiluted vinegar left to stand, so dilute it and rinse afterwards.

Scrap steel has real market value, so a dead stainless pot or bottle is one of the few household objects that actually gets recycled rather than theoretically recycled - scrap yards take it by weight and most curbside metal streams accept it clean. Nothing about it degrades, so the realistic failure mode is being thrown out, not wearing out. Vacuum-insulated bottles are the awkward case, since the welded double wall cannot be separated at home.