This week’s expression is, “Boire du petit-lait” (sometimes appearing as “Boire son petit-lait”).
The literal translation is, “drinking whey” (sometimes appearing as “drinking one’s whey”) and it means basking in praise or flattery, or taking obvious pleasure in a situation that has turned out to one’s advantage.
Example: “Les invités s’accordèrent à dire que c’était la meilleure blanquette qu’ils aient jamais mangée. Derrière son sourire modeste, la maîtresse de maison buvait du petit-lait.” “The guests agreed it was the best veal blanquette they’d ever had; underneath her humble smile, the hostess was drinking whey.”
Listen to the idiom and example read aloud:
According to these sources, the expression started out in the 16th century as Avaler doux comme lait (swallowing soft as milk). It became boire du lait (drinking milk) in the mid-19th century, and the milk became whey (the literal translation of petit lait is “small milk”) in the mid-20th century.
The older expressions likely allude to the rapture with which a baby drinks milk, while the modern usage refers to the fact that whey, a nutritious by-product of cheese-making, used to be considered a treat. It is now, I am told, fed to pigs, which reminds me of another expression, c’est de la confiture pour les cochons (it is jam for pigs, the French version of pearls for swine), but I digress.
Before we part, I should note that this week’s idiom is not to be confused with its close cousin, “Ça se boit comme du petit-lait” (it drinks like whey). This one is equivalent to the English expression, “it drinks like water,” meaning that an alcoholic beverage is very easy to drink; it is usually implied that said beverage is, therefore, a little treacherous. Example: “Il faut que je me méfie, ce punch se boit comme du petit-lait.” “I should be careful, this fruit punch drinks like whey.”