I've had a Belgian Strong Dark Ale (approx. abv 9.1%) in secondary for a month now. It's developing a clear separation band in colors. In other words, the top inch is a darker brown, while the remainder (aside from the trub at the bottom) is several degrees lighter. The boundry between the two shades is clearly delineated. Any ideas as to what has caused this?
By way of background: nothing out of the ordinary occurred during brewing or primary. Primary was controlled at between 64 and 66 degrees F. Secondary has been a bit different, as it's stored in my basement storeroom. Down there, the temperature has dropped to a range of 50 to 55 degrees F. Could this colder temperature be causing the separation? What is the separation?