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I've been told that its not safe because of the temperature difference, but I also know that people put whipped cream on stuff like hot chocolate, so why wouldn't it be safe to put cold foam on hot coffee?

Enrico Tuvera Jr
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    What do you mean by "unsafe"? Food poisoning? Cause a hot coffee explosion? Something else? – FuzzyChef Oct 17 '21 at 00:27
  • @FuzzyChef Someone told me that mixing hot coffee and cold milk causes a chemical reaction that creates some kind of toxin, although a cursory search didn't wield any result. – Clockwork Oct 17 '21 at 14:09
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    "Someone" is pranking you, I think. – FuzzyChef Oct 17 '21 at 17:53
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    @FuzzyChef The most likely result I could come across was the fact that some people have more trouble digesting milk, and mixing it with coffee makes it even heavier on the stomach, although for many others (like myself) it's not a problem. – Clockwork Oct 17 '21 at 20:18
  • I've been told that eating/drinking two things with large temperature differences (i.e. ice cold water and hot soup) is detrimental to your teeth. But I haven't found anything online to support that. Perhaps that could also be what led to this question? – Cave Johnson Oct 18 '21 at 17:38
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    @Clockwork There is no plausible mechanism for that which would be potentiated by adding cold milk to hot coffee. – Sneftel Oct 18 '21 at 18:13
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    @CaveJohnson I'm not entirely sure, but I remember something like this: if you pour a hot beverage into a cup, then after emptying it you pour a cold one into the (now hot) cup, then it might crack or break because of the sudden temperature difference. – Clockwork Oct 18 '21 at 19:03
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    @FuzzyChef I assume OP means "unsafe" in the realm of a TCS food (Time/Temperature Controlled Safety) of which milk definitely is one. Putting cold milk into hot coffee would raise the temperature of the milk into the danger zone and plausibly, if left there long enough then bacteria could grow. But what must be remembered is that the safety of TCS foods depends on both time and temperature, so pouring cold milk into hot coffee should be safe as long as you drink it in a reasonable time. – Glen Yates Oct 18 '21 at 22:51
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    https://scomedy.com/quotes/3147 – Scott Seidman Oct 19 '21 at 02:56
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    @Clockwork If a housemate was to pour boiling water into a moulded dimpled *glass* pint tankard, it would break along the mould line. (No attempt was made by the housemate to replicate the experience.) – Andrew Morton Oct 19 '21 at 16:03
  • @Clockwork Is this the age-old [question](https://www.goldenmoontea.com/blogs/tea/106691847-milk-before-or-after-your-tea) of milk-before-tea or tea-before-milk? Bone china is more resilient than many people think. – doneal24 Oct 19 '21 at 17:11

4 Answers4

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There is no safety issue with adding cold milk foam to hot coffee. Coffee aficionados recommend against adding cold milk to hot coffee, because they suggest it compromises the flavor of freshly brewed coffee. Their recommendation is that any milk, foam or not, should be warmed, but it is not a food safety issue.

briantist
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moscafj
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There's no plausible mechanism that would make it unsafe. It's usually impractical though, since milk foams better when heated. Steaming it automatically heats the milk, and most mechanical ways of doing it work best if you heat the milk first.

It's not quite cold foam on hot coffee, but one popular dessert in Italy is affogato. At its most basic, it is a scoop of vanilla ice cream topped with a shot of espresso, i.e. very cold milk product and very hot coffee served together.

user141592
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    Since we're mentioning Italian coffee habits, let me add that both putting hot milk (*macchiato caldo*) and cold milk (*macchiato freddo*) on espresso are in wide use here. – Federico Poloni Oct 18 '21 at 19:31
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I suppose it's unsafe in a way similar to drinking microwaved liquids:

Customer may feel the cold foam and take a big sip, not immediately noticing that the coffee itself is boiling hot?

Stefan Haustein
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  • Also, could it cause a [microwave superheated liquid](https://www.youtube.com/watch?v=FsjuM1kR7-w) to bubble over? – Richard Oct 17 '21 at 21:56
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    That video is not what a normal person does. If you microwaved a cup of water repeatedly a dozen times, causing all dissolved air to be released, then yes, this can happen, but you can do this just the same with a normal kettle. This is a deliberate act to create conspiracy though. Superheated water isn't new, but you have to do something extraordinary to create it, and it's just not something you do by accident very often. – Nelson Oct 18 '21 at 03:06
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    One can create superheated water completely by accident, but coffee is surely not the substance to start with. – fraxinus Oct 18 '21 at 16:59
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    @Nelson - I did it once, purely by accident, which is why it occurred to me. – Richard Oct 19 '21 at 07:08
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You may be thinking of the reverse: pouring hot, steamed milk over ice. There is an idea floating around out there that this is dangerous because it creates conditions for harmful bacteria to grow:

“Pouring hot, steamed milk and foam over cold ice can allow for the growth of bacteria. Even though it’s a small risk, it’s still a risk.” [1]

I have heard this from baristas myself, and it appears to be present on barista forums: [2], [3]

As to whether this has any scientific grounding, I have no idea. Just passing on that some baristas hold this view, and I have seen at least one refuse someone who asked for steamed milk over ice. I myself am not worried, and love an iced capp from Wrecking Ball: [4]

Glorfindel
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Graham Place
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    That would make sense only if the consumers intended to let their drink stand around for two hours or more. But then, that’s an issue of perishable food spending time in the danger zone and absolutely not about combining something hot and something cold. That said, your first link ignores the time aspect, in the second and the third, users already debunked the assumption. The fourth was frankly too long to bother with and resembled advertising. – Stephie Oct 19 '21 at 18:45