It's sugarcane juice that's boiled, not pressed cold — simmered with cinnamon and cloves until it tastes closer to liquid spice cake than plain sugar water.
Qasab is a Libyan sugarcane drink made by boiling cane juice with warming spices such as cinnamon and clove, then straining it and serving it hot in winter or over ice in summer. It's sold by street vendors in Tripoli's markets alongside other seasonal favorites like the dried-apricot drink qamar al-din.