Why is it that milk will curdle if you add it to hot water or to tisane (herbal tea), but not if you add it to black tea, coffee, or hot chocolate? All of those things are just plant parts steeped in water.
I’m guessing it has something to do with the fact that black tea, coffee, and chocolate are all basic (alkali). Lemon juice and vinegar curdle milk because they are acid. Milk solids do not normally clump together because their surfaces are electrically charged and repel each other. An acid attracts these solids, allowing them to coagulate. Disclaimer: I am not a chemist, and it has been a long time since I learned this.
How old is your milk, and is it whole milk or skim?
In my experience, milk that is about ready to turn will be more anxious to curdle than fresh-off-the-shelf milk, and whole milk more than skim. Of course, there are people who feel that skim milk isn’t really milk…
Update your refrigerator, boy. 