The effects of temperature (116 °C, 150 °C, and 183 °C) and flow rate (66, 150, and 234 mL/min) on the fractionation of triticale straw into different products was determined using a flow-through pressurized low polarity water reactor. The greatest concentration of biomass was hydrolyzed and extracted in the first two of eight 600 mL fractions (1.2 L), after which dry matter yield decreased. Carbohydrate, lignin, acetyl group, and uronic acid yield increased with temperature, but there was no effect due to flow rate. Most dry matter extracted at 116 °C was probably associated with the extractives. Xylan yields decrease slightly at the highest flow rate due to a decrease in the residence time of the acids produced in situ. Carbohydrates were extracted mostly as oligosaccharides, and the highest processing temperature resulted in the production of furans from the xylose and arabinose in the liquid extracts.