Fermentable sugars are carbohydrate substrates that a particular microorganism or cell system can transport and convert through pathways that generate energy and defined end products under specified conditions. The category includes monosaccharides such as glucose and xylose, disaccharides such as sucrose and maltose, and hydrolysis products released from starch, cellulose, or hemicellulose ^[1]. Fermentability is therefore organism- and process-specific: a sugar must be chemically accessible, recognized by a transporter, phosphorylated or otherwise activated, and connected to a catabolic route that supports cellular redox and energy balance ^[2]. Mixed hydrolysates may contain sugars that are consumed sequentially because of carbon catabolite repression, transporter competition, or differences in pathway regulation ^[3]. Pretreatment can increase sugar release, but it may also generate furfural, hydroxymethylfurfural, phenolics, or organic acids that inhibit growth and fermentation. In a bioprocess, the relevant sugar pool is consequently determined by feedstock composition, hydrolysis efficiency, uptake capacity, regulatory state, and inhibitor tolerance rather than by carbohydrate concentration alone ^[1][4].