# Chemistry of congealed milk **URL:** \ **Category:** Factual Questions\ **Created:** [April 13, 2022, 2:57pm UTC](https://boards.straightdope.com/t/chemistry-of-congealed-milk/962776 "2022-04-13T14:57:13Z")\ **Posts on this page:** 1\ **Showing post:** 3
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [April 13, 2022, 4:08pm UTC](https://boards.straightdope.com/t/chemistry-of-congealed-milk/962776/3 "2022-04-13T16:08:37Z")
Yes, **naita** is correct. The acid in the coffee is causing the curdling, and this is more likely to happen as the milk gets closer to being spoiled. > …This is because coffee and tea contain just enough acidity to tip the pH of milk to the point of curdling. The effect is most often seen in milk that is close to going sour or when adding milk to very hot coffee or tea, since the high temperature can coagulate casein. Side note: you’re making a _[café au lait](https://coffeeaffection.com/cafe-au-lait-vs-latte/)_. That sounds much more sophisticated than a “poor man’s latte.” > **[Why Milk Curdles](https://sciencenotes.org/why-milk-curdles/)** > > Chemical reactions cause milk to curdle. Here's a look at the factors leading to curdling and how to prevent milk from curdling or cause it occur. --- _[View the full topic](https://boards.straightdope.com/t/chemistry-of-congealed-milk/962776)._