TL:DR: All Gamut Academie strings (pure gut and gut/metal-wound) are made with beef serosa unless they specifically say “sheep gut.” All pure gut Tricolore violin and viola strings are made with sheep gut; gut/metal-wound Tricolore and all Red Diamond strings are made with beef serosa.
Playing with natural gut strings brings about distinctions in feel, responsiveness, and overall playing experience. Gut strings are generally softer and more pliable under the fingers than synthetic strings, providing a tactile and intimate experience. Due to their flexibility, gut strings respond well to subtle changes in bow pressure and finger placement, allowing for nuanced expressiveness. They are capable of a wide dynamic range and can produce a rich palette of tones.
Sheep gut strings have slightly different properties than beef gut. In broad terms, it has a warmer tone. One of our clients with a poetic flair describes sheep gut as having a “golden” tone and bovine serosa having a “silver” tone.
Our Playing With Gut Strings section provides an entire section on the differences and nuances of playing with natural gut strings.