That from reader Trish, and it’s an interesting question. I’m not up on the finer points of cow metabolism, however I do know that cows that are grazed on open pastures tend to give milk that makes soft butter. Something about what happens when polyunsaturated fats are processed into milk inside the cow…I’m hazy on just how that occurs. Of course cows can only graze when the weather is good. Even in regions that don’t get much snow, grasses start to transfer their nutrients down into their root systems in the winter time, rendering the leaves close to useless as a food. Farmers therefore must supplement the cows’ diets in one way or another, usually with hay or grain, and it’s this diet that generally leads to firmer butters. Thus the very same dairy that sold you a nice, firm pastry butter in winter might well sell you a softer, less pastry-friendly butter in spring and summer.