Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering


A continuous cooker for 0.2 kg/min of ground corn (Zea mays) was developed to match the expected alcohol fuel needs of a 300 ha Iowa farm. A commercial jet cooker (Hydroheater ('TM)) was used, but the design and implementation of the slurry handling, enzyme dosage, pH adjustment, and automatic control were local;Pure corn starch and corn meal were used as feedstocks. Solids concentrations from 10 to 27% w/w were examined. The feedstocks were hydrolized with alpha-amylase at temperatures from 97 to 124(DEGREES)C, and saccharified at 60(DEGREES)C with amyloglucosidase. Slurry samples at four locations were analyzed for total reducing sugars (TRS). The same jet cooker was used under laboratory conditions to cook small batches of slurry; saccharification was done as a batch;Problems with the acid and base metering pumps led to poor pH control. The results for both cookers were analyzed using a response surface technique, because pooling all the results was expected to give some indication of the performance of a farm scale cooker operated with unsophisticated controls. The dependent variables were: (1) material efficiency, the fraction of starch converted to TRS, (2) conversion ratio, the ratio of TRS in the output supernatant to the input solids concentration, and (3) energy ratio, the ratio of the higher heating value of the TRS produced to the electrical and steam energy during conversion. The independent variables were solids concentration in the input slurry and the temperature of the cooking process. Solids concentration was not a significant factor in material efficiency or conversion ratio, but did explain a significant amount of the variability in the energy ratio for both feedstocks. Physical handling will limit solids concentration in continuous cookers, but a high energy conversion ratio requires solids concentrations > 0.22 kg/kg. The cooking temperature was significant in explaining variation in all the dependent variables. For both feedstocks, the energy ratio increased with solids concentration and decreased with temperature. Material efficiency and conversion ratio were highly correlated. Material efficiency for starch was maximum at 106(DEGREES)C, but was still increasing at 124(DEGREES)C for corn. Before continuous cooking can be used successfully at the farm scale for corn meal, the solids handling capability of small jet cookers must be improved. Farm-scale cookers must incorporate pH control to (+OR-)0.1 pH.



Digital Repository @ Iowa State University,

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Jonathan Chaplin



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146 pages