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Comment by carterschonwald | Hacker News Reader

So there’s several details and questions that I think might be important for interpreting this study!

1) all stainless steels need to be “passivated” in order to be properly stainless. These days that process involves putting the stainless steel in a hot water bath with like a pound of citric acid for every gallon of water used. (I actually do this at home with any cookware or steel bottles where I notice a metallic taste). Chips of stainless steel that aren’t passivated will leach and or corrode!

2) I think most cookware is 304 steel. I’m not sure how often it’s 316. But also unless you control for passivation it’s still pretty uninformative.

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When welding stainless used in food service, you then need to re-passivate all the joints. Can be a bit of a pain for long pipelines. You'll often see acrylic piping used in food plants partially for this reason (another reason is that it's easy to see any blockages or growths etc through the pipe walls).

Does occasionally cleaning my cookware with Barkeeper's Friend (oxalic acid) accomplish the same?

I don’t know! With citric acid and it’s predecessors, they only dissolve iron atoms but don’t react with the chromium and nickel alloying elements, which is an important combo!

I found this passage. Doesn't really explain the process though.. natural oxidation completes in the air 1-2 weeks?

>To passivate stainless steel at home without using a nitric acid bath, you need to clean the surface of all dirt, oils and oxides. The best way to do this is to use an oxalic acid based cleanser like those mentioned below, and a non-metallic green scrubby pad. Don't use steel wool, or any metal pad, even stainless steel, because this will actually promote rust. Scour the surface thoroughly and then rinse and dry it with a towel. Leave it alone for a week or two and it will re-passivate itself. You should not have to do this procedure more than once, but it can be repeated as often as necessary.

https://spaco.org/Passivate.htm

> all stainless steels need to be “passivated” in order to be properly stainless.

Does the passivated layer survive scrubbing and dish washing?

It can be damaged physically or chemically but the oxide layer is self-healing upon contact with oxygen.

The depth of the chromium-rich top layer would be measured in nanometers at most, while a visible scratch would have to be tens of microns in size.

Isn't stainless steel a uniform alloy of chrome, nickel and iron?

It would be if you made it in space, but in the presence of oxygen, or when the factory dips it in acid which is what they do, the surface is depleted of iron and enriched of chromium to a depth of a few molecules. Below that is a thicker nickel-rich region.

Nobody really knows how this migrating is happening at a low level, by the way. Mystery of material science.

Soda is acidic and comes in Aluminum cans. Why don't the cans develop holes?

"The inside of the can is lined by spray coating an epoxy lacquer or polymer to protect the aluminum from being corroded by acidic contents such as carbonated beverages and imparting a metallic taste to the beverage."

https://en.wikipedia.org/wiki/Aluminum_can

I often wonder how good that coating is for consumers. I'd be surprised if it doesn't leach into the produce.

Certainly a belief among some that soda from a glass bottle tastes notably better.

That has more to do with the use of cane sugar vs corn syrup

Mexican Coke, which uses cane sugar, comes in a glass bottle, but you can also get US coke presumably with corn syrup in a glass bottle and some people do think it tastes better.

> Mexican Coke, which uses cane sugar

This is at least partially a myth.

Here's a study which found no sucrose in Mexican coke: https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2010.25...

Though, it is complicated because there are multiple bottlers making multiple different coke products, and even the same bottlers could shift what sweeteners they use over time, presumably based on pricing.

I'll vouch for that when it comes to beer. It's not just the packaging itself though, but also the experience. Plus, when you drink from a can directly, your lips will touch the outside / top aluminium, which will affect the flavor and experience - subtly, but it's there.

I prefer glass bottles for my beers.

> when you drink from a can directly, your lips will touch the outside / top aluminium, which will affect the flavor and experience - subtly, but it's there.

Ahhh the subtle flavours of rat shit. I've never seen someone wash the top of a can before opening it. I mean, would you go around licking random surfaces that other hands have touched, rodents have scurried over and defecated on, etc?

The odds that a hand or rat has touched the top of a can you just pulled out of a box is pretty slim

As an aside, to me Coke from can has a different feel from Coke from plastic bottle. Almost as if the bubbles are fewer and larger when sipping from a can.

Well the carbonation is different for cans vs bottles, and also dependent on the bottling plant.

The epoxy resin is mostly BPA. [1]

[1] https://www.coca-cola.ca/faqs/coca-cola-faqs-health/do-coca-...

The article you linked talks mostly about BPA, but the resin only contains it...

sorry, I didn't mean by volume, but rather that when folks say resin they mean bpa epoxy resin.

Then you should also worry about plastic water bottles...

Depends on the kind of bottle; polyethylene, safe; polycarbonate, not safe; polyethylene terephthalate, not great.

Just about every disposable water bottle is PET, which is far down the list of dangerous plastics when it comes to leaching (to ignore for a moment microplastics).

Because they’re really a plastic bag with aluminium lining. Nurdrage has a good video showing this: https://m.youtube.com/watch?v=X1pB6O6AYMU

lovely vid and great channel

If the cans weren't lined (like other commenters remarked), the most the acid in the soda would do is dissolve a little bit of the aluminium - of course that's not necessarily healthy, but to get a hole in the can you'd need something much stronger. Despite what some urban legends claim, there is still a difference between Coca-Cola and hydrochloric acid...

Aluminum soda cans are lined with BPA or similar.

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