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They say you can get the whipped cream or egg whites "higher" or "stiffer" if you use a copper bowl. Why is that?

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Yes, as mentioned previously it is beneficial to whip egg whites in copper bowls BUT it is important to note that the impact on the egg whites from the copper is primarily beneficial for applications where the final product is going to be baked. You will generally not notice any increased volume in the whipped egg whites themselves, compared to what you'd get without a copper bowl.

As the whites are whipped the copper bonds to create a copper salt that increases the temperature at which the proteins will coagulate. The copper salt makes them more pliable and able to better expand without rupturing. Under "usual" conditions (glass, stainless steel, ceramic) they will coagulate at around 160F degrees. When whipped in a copper bowl they have to reach 170F degrees before they coagulate. This means that they will have a 10 degree increase in temperature to continue to expand and increase in volume.

This also means that if you're talking about whipping egg whites for meringues, dried for cookies or other desserts, the expense of a copper bowl will not be worthwhile as you're not looking for expansion properties in these items. If you're doing a lot of cakes and souffles then a copper bowl would certainly produce better results.

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    Wouldn't the copper added to the food also add toxicity? I remember that the old practice of boiling a copper penny with cabbage was discouraged for that reason.
    – Kevin Keane
    Commented Nov 20, 2015 at 0:56
  • @KevinKeane - I'm not sure myself, but it might be a question of quantity. I would intuitively expect less copper leaches out of copper in a cold mixing scenario then in an active boiling, even if the bowl does have more copper than a penny. The amount leached into a serving of egg whites may not be enough to be dangerous, or the frequency of making whipped egg whites and amount consumed over time may be assumed to be less than boiling cabbage (which can be a staple food). Copper is needed in trace amounts, I think it is only unsafe if people are getting a lot.
    – Megha
    Commented Nov 18, 2016 at 2:39
  • Also, acidity seems to play a role in whether you get the really toxic copper salts (IIRC copper acetate is real bad news). Another reason might be that copper has interesting thermal properties (can stay chilled due to being heavy, and is very good at making everything else cold that contacts it).
    – rackandboneman
    Commented Nov 18, 2016 at 10:55
  • @rackandboneman you might be on to something. One, admittedly very vague, article (bon-vivant.com/chemistry-copper) claims that egg whites do not get toxic from copper - and they go on to say that you should not use an unlined copper bowl for any other kitchen purpose.
    – Kevin Keane
    Commented Dec 4, 2016 at 6:08
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According to wikipedia, the copper bonds to the sulfur in the egg whites, which has the effect of stabilizing the foam.

http://en.wikipedia.org/wiki/Egg_white#Copper_bowl

Cookwise by Shirley Corriher says the same thing.

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  • As does The Guru, Harold McGee.
    – daniel
    Commented Aug 1, 2010 at 21:06
  • If it is about sulfur, the whipping cream should be unaffected.
    – rackandboneman
    Commented Nov 18, 2016 at 10:56
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For whipped cream it helps to have a metal bowl if you cool the cream while you whip by dipping the bottom of the bowl in ice water. You might need to do this if, for example, the cream is warm to begin with.

I couldn't say though if a copper bowl would work better than any other metal bowl.

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  • Probably a good thing that we have definitively answered that question, then.
    – daniel
    Commented Aug 1, 2010 at 22:50
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    This works for whipping cream because as the cream is whipped, it's the fat globules that bond with one another, trapping air in the process. A chilled bowl, especially metal, helps the fat to firm up and bond together more easily. The opposite is true for egg whites. Many people confuse the fact that since they both get whipped and end up white, light and fluffy that the same is true for both. Not the case. Egg whites should be room temp. or even slightly warmed to encourage the proteins to unwind and link together to trap the air. Copper only has an affect on the egg whites.
    – Darin Sehnert
    Commented Aug 2, 2010 at 4:31
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I recently bought a copper bowl and whipped ONE egg white in it ending up with enough fluff to fill three ramekins for apricot shuffle.

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    Hello, and welcome to Stack Exchange. While interesting, this doesn't answer the original question.
    – Daniel Griscom
    Commented Nov 17, 2016 at 19:08
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    I'd convert this to a comment on that answer, but... it seems like you're just misunderstanding the answer. It's not saying they don't increase in volume when whipped, it's saying there's not an increase in the resulting whipped volume when using a copper bowl compared to what you get without a copper bowl. So I edited the answer to clarify that, and I think we're all sorted.
    – Cascabel ♦
    Commented Nov 17, 2016 at 20:07
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    As for your actual statement about whipping in a copper bowl, I think you're saying that's more fluff than you'd get without the copper bowl? but it's not totally clear.
    – Cascabel ♦
    Commented Nov 17, 2016 at 20:08

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