Instrumental This is obviously a John Skehan tune, since Isinglass is/was a key ingredient in Guiness for generations. It's used to clarify the beer by causing sediment to drop out of suspension. It is also made from fish stomachs, which means that vegans couldn't drink Guiness. As part of a marketing push recently to make it veg-friendly, their use of isinglass has been discontinued. -- jgrubb