Published March 1, 2013. From Cook's Illustrated.
Butter keepers promise to keep sticks fresh-tasting, so we stored unwrapped butter in seven keepers ($5 to $35) for several weeks and tasted them daily.
Keeping an unwrapped stick of butter on hand makes buttering toast, greasing cake pans, and slicing off a pat mid-sauté fast and convenient. But butter’s high fat content means it readily picks up off-flavors, whether it’s onions, last night’s chicken, or the staleness of the fridge. Butter keepers promise to keep sticks fresh-tasting, so we stored unwrapped butter in seven keepers ($5 to $35) for several weeks and tasted them daily. Our first discovery: Air is the enemy. A ceramic model with visible gaps between the lid and the base let butter pick up an “off” taste in just three days. Two non-airtight stainless steel models surrendered freshness on day four; two plastic keepers with loose latches gave up the ghost on day five. That left two completely airtight models still in the running. But one had blue ink markings on its base for portioning butter that streaked during washing; the ink on a backup model (which we didn’t wash) smudged with a mere swipe of our thumb. Our winner has engraved markings for easy measurement, a removable tray for table service, and a shape that fit a range of stick sizes. Most important, it kept butter fresh-tasting for more than 10 days.