These bottle caps are perfect for brewers afflicted with tactile hyposensitivity, or anyone who's ever thought, "This beer feels cold, but it doesn't look cold." Take the guesswork out of chilling your homebrew with these amazing cold-activated crown caps. They begin to change to a blue color at approx. 46 degrees, and reach "maximum blue tonality indication" at 41 degrees. What does that mean? If the cap is blue, you've got cold brew. They're fun, inexpensive, a little out of the ordinary, and a good way to start a conversation about your homebrew.