The rate and extent of fouling in a single tube wort boiling system

Wort is the fermentation feedstock that provides all the necessary sugars and nutrients required for successful brewing. It is boiled to stabilize its composition prior to fermentation, a process that leads to the coagulation and subsequent flocculation of proteins and tannins, and fouling of the heat transfer surfaces. Fouling by commercially-supplied wort was studied in a single-tube (15 mm x 0.2 mm wall thickness, with wall temperature control) model wort boiling system, I at wall temperatures of 130, 150 and 170degreesC and flow velocities of 0.07, 0.14 and 0.18 m s(-1), with the overall objective being to identify modes of operation which prolong operating times. Heat transfer was quantified in terms of the amounts of heat transferred to the liquid and vapour phases. The influence of operating conditions on the fouling process was determined by calculating the decrease in heat transfer coefficient with the increasing number of batches of wort processed. The work quantified the influence of wall temperature, wort velocity (and hence circulation time) and the duration of the boil. Fouling showed little temperature dependence as for all wall temperatures, a constant rate of fouling (dR(f)/dt) was determined; dR(f)/dt = 1 x 10(-5) m(2) kW(-1) h(-1), in the absence of vapour condensation and dR(f)/dt = 2 x 10(-5) m(2) kW(-1) h(-1), with vapour condensation. The rate of fouling in the system was more affected by wort velocity, particularly under conditions where vapour was condensed. Under these conditions, curves obtained for velocities 0.07 and 0.14ms(-1) showed an initial, more rapid rate of fouling, which then continued at a reduced rate. The initial rate of fouling doubled as the wort velocity halved (at wort velocity 0.07 m s(-1) initially dR(f)/dt 4 x 10(-5) m(2) kW(-1) h(-1) compared to dR(f)/dt = 2 x 10(-5) m(2) kW(-1) h(-1) at velocity 0.14 m s(-1)), whereas the final rate was the same at both velocities (dR(f)/dt = 8 x 10(-6) m(2) kW(-1)h(-1)).