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Jul 28, 2004 06:20 AM

what's up with my milk curdling in my coffee?

  • d

Milk was well within its use-by date. Same coffee I always use (instant, okay, don't mock the afflicted... freshly boiled water from the cold portion of the tap). I busted into my emergency stock of UHT milk, and THAT curdled too! The uht curdled in smaller chunks than the regular milk. Could there be something weird going on with my tap water? It's extremely hard water as it is.

Any help with the mystery would be appreciated...

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  1. I see that with known good milk sometimes, too. At one point I theorized that the coffee was too hot at times, but this is probably hooey.

    Half the time I just drink it anyway.

    1. Probably unrelated, but if you put Kahlua in a cup and pour in UHT milk (mine is cold, but not sure if it matters), you get the dance of the fireflies!

      Most people pour Kahlua into the milk, and so don't see this display. I don't know why it happens, but it really freaked me out the first time.

      Even more freaky is to nuke coffee & milk/cream/whatever in a cup which narrows slightly as it goes up. A mug shaped a bit like a beanpot or a beehive, for example. If you do it right, it heats up to some critical temperature, but a skin keeps it in place. Or something, I'm no physicist.

      In any case, as soon as you pop the surface (I use a chopstick, a regular stirrer will also work, not so sure about a spoon - might be too wide), the whole thing blows up and over the cup at you, like that baking soda volcano you built in the third grade!

      I think the decreasing radius of the mug is critical. I am less sure about the cream, but I think it too has proven necessary. Haven't really experimented with this - it happens occasionally when I'm reheating a mug of coffee and carelessly give it a quick stir. It makes a terrible mess.

      4 Replies
      1. re: JillHerndon

        You can prevent this by nuking it with the chopstick in the mug. I assume this is the same phenomenon as superheating water -- if the water is undisturbed, you can actually heat it past the boiling point without bubbles forming. Once it is disturbed, by, say, a quick stir, all the extra energy makes bubbles all at once, and it, as you say, explodes. this can be pretty dangerous, what with the flying boiling liquid, so always micro-ing with a utensil in the mug is a good idea. (non-metal. Don't want any lawsuits.)

        The smaller surface area probably does allow this to happen more easily, as it makes the volume more stable and less likely to be disturbed.

        Can't speak to the fireflies in your Kahlua, i'm no chemist. Are you saying it actually lights up? I've only seen this chewing mints.

        1. re: jessi

          No, I think the term I should have used was "screaming Mimis". I mean all these particles (?) go zipping around every which way, like the thing's possessed. Depending on how much you've already drunk, you can convince yourself that you're watching molecules in some sort of cloud chamber.

          Again, I think *UHT* is critical. Have never noticed it with regular milk. Nor if you put the milk in the cup first.

          FWIW, I usually have it in a mug. Don't think this is critical on this one tho.

          1. re: JillHerndon

            Okay I sorry but I have to know, what is UHT Milk? I know it's probably very obvious but I just can't figure out what it stands for.

            1. re: Kristine

              "Ultra-Heat Treated", is it? Boxed milk which needs no refrigeration until opened. Shelf life of at least a year. Up to 10 in some cases.

              Bit of a novelty in the US, but very common abroad. The default in many countries, in fact. Hence the term "fresh milk" there for what we would likely dub "regular" here.

              Depending on brand, UHT milk has a bit of a chalky taste, like what you'd get reconstituting powdered milk at home. I believe this "powdery" nature has something to do with the "particles" zipping around on the Kahlua, but I'm well out of my league here. And on my 5th glass.


      2. It seems to me that coffee will curdle milk if it is very acidic and very hot.

        Also, the use date on the milk may not account for lax handling.

        That will be $0.02, please.


        1. To actually reply to your post. If you've got raw garlic sitting open in your fridge it can curdle milk

          1. Instant coffee is generally more acidic than "normally" brewed coffee. This is probably most often due to treatment--overextraction produces an undesirable acidity. In general, darker roasts are milder and lighter roasts are more acidic; the act of roasting destroys the acidity. (Actually, acidity has to do with a variety of factors: bean type--Arabicas are more acidic; processing: wet/washed processing is more acidic; roasting: pressure roasted as well as lighter roasted; and method of brewing: I have no idea which produces a more acidic cup but I'd suspect percolating and cowboy style are high on the list.)

            You could try buying a dark roast instant. Incidentally, the temperature of the coffee also effects the speed of milk curdling (i.e., the hotter it is, the faster the milk will curdle). So... drink your instant cold (!) and fast.

            I'd recommend, however, going to the store and buying a french press. It doesn't take too much more work to produce a french press cup: boil water, place grounds in press (real, not instant), pour water in, wait a couple minutes (the hard part), press (the fun part), et voila! Instant coffee snobbery as opposed to instant coffee (with curdled milk in it). Yuck.