Why did cream curdle when added to ale broth for mussels?

My sister replicated a recipe of mine (http://theyearinfood.com/2011/03/mussels-and-fennel-in-ale.html), which I made without a hitch. When she added cream to the broth, which is composed mostly of Belgian ale, it curdled. Any thoughts? My instructions said to turn off the heat before adding the cream, which she forgot to do. Could it be that? Could it be the type of beer used (perhaps a beer with more acid would cause this)? Cream vs. half and half? She's asked my advice and I'm at a loss.



theyearinfood March 20, 2011
Thanks so much, guys! Question answered. Foodpickle is awesome.
littleknitter March 20, 2011
Oh, and yes, the heat definitely makes a difference. Heat cause the curds to expel whey because they contract, thus expediting the curdling process. I suspect that the added heat from forgetting to turn off the burner contributed to the curdling and the difference in acidity between beers may also have been crucial to whether or not the sauce curdled.
pierino March 20, 2011
Your first thought about off heat was correct. And whisk it in slowly don't just pour it in all at once because after that it's hopeless.
littleknitter March 20, 2011
It curdles because it's coming into contact with an acid, aka alcohol - the acid, particularly when combined with heat, makes the casein in milk products coagulate. It's the same process as cheesmaking.
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