I travel to work on the train and I usually take an insulated travel mug of coffee to drink on the way (the kind with a screw-on lid with drinking spout you hold a button down to open. This morning, my coffee tasted just the same as usual, but when I had almost drained it, suddenly my mouth was filled with… bits :eek:
On closer inspection, the bottom of the mug was filled with curdled white milk bits. They didn’t taste icky, but still…
So what’s going on? The milk didn’t taste off, and I made the coffee the same as always. Why would my morning beverage turn on me this way?
Milk acidifies as it goes bad, but it’s buffered ~6.5-6.7, so it may be well on its way to funk without actually tasting off. Coffee is acidic, and may push it over the edge. Along with the heat. Both low pH and heat will denature the proteins, which then aggregate.
It may have just started to go off. Or the coffee was actually so hot that it curdled the milk. Skim will also curdle more quickly than whole milk. But, in my experience, it’s always been a sign the milk was at least starting to go bad.
Sometimes milk droplets will catch in or around the spout of the jug, congeal, and form a very small crust. You may have loosened them up while pouring in your milk this morning. I’ve seen it a few times when making tea or coffee at home.
IME when milk curdles in hot coffee the rest of the milk in the carton will taste slightly creamy and slightly sharp. IOW, it’s juuuust beginning to go off. Still safely edible for another day or so, but getting iffy quickly for folks with weak or suggestible stomachs.
I had the same thing happen with some fairly old UHT milk. The milk was perfectly edible but had partially dehomogenized and only made worse by the addition to hot coffee. I imagine that non-UHT milk tends to spoil before the curdling becomes an issue, but maybe not always.
This. I worked last shift for awhile at a place that put jugs of half & half on the tables. One of the close-up tasks was getting a big cup of hot coffee and testing the jugs. Jugs that didn’t curdle were consolidated for use the next day.
Most didn’t curdle, because we went through the half & half pretty smartly. But the ones that did curdle were obvious. You’d have to go get another cup of coffee to keep testing after finding one.
Somewhat related story: my mother used to leave a vinegar solution in our kettle overnight to remove limescale. One morning I came downstairs to make a cuppa (not realizing that what was in the kettle was the vinegar solution rather than water). I noticed an odd smell in the kitchen when I boiled the kettle, but didn’t think anything of it.
I was in the habit of pouring my milk into the mug after putting the teabag in, rather than pouring it after the bag had steeped in water. So I poured the milk over the teabag, then went to pour in the water from the kettle.
The milk immediately exploded into a frothy marshmallow-y concoction that just kept increasing in volume until it burst over the edges of the mug. It was terrifying - like I had unwittingly unleashed a demon from the teabag. I screamed.
Eventually everyone else came downstairs and my mother explained that she’d been descaling the kettle, and we had a good laugh, but there was yoghurt-y stuff all over the counter.
