The effect of the reaction temperature on hydrothermal liquefaction of dried distillers grains with solubles (DDGS) was investigated using a novel stop-flow reactor system at varying temperatures (300–400 °C), fixed pressure (250 bar), and fixed reaction time (15 min). The stop-flow reactor provides rapid heating of biomass feeds and the option of performing multiple sequential repetitions. This bypasses long, uncontrollable temperature gradients and unintended changes in the reaction chemistry. The product, a crude bio-oil, was characterized in terms of yield, elemental composition, and chemical composition. Higher reaction temperatures resulted in improved bio-oil yields, less char formation, and higher heating values of the bio-oil. A supercritical reaction temperature of 400 °C was found to produce bio-oil in the highest yields and of the best quality.