TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In the method above, the fermentable carbon substrate is derived from a grain or sugar source selected from wheat, corn, barley, oats, rye, sugar cane, sugar beets, cassava, sweet sorghum, or their mixtures. The fermentable carbon substrate is derived from cellulosic or lignocellulosic biomass selected from corn cobs, crop residues, cornhusks, corn stover, grasses, wheat straw, barley straw, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers, animal manure, or their mixtures. The fermentable carbon substrate is selected from monosaccharides, oligosaccharides, and polysaccharides. The fermentation culture is maintained under conditions selected from anaerobic conditions and microaerobic conditions. While growing the production host in (c) at a first temperature over a first period of time, a metabolic parameter of the fermentation culture is monitored, where the metabolic parameter that is monitored is optical density, pH, respiratory quotient, fermentable carbon substrate utilization, carbon dioxide (CO2) production, and isobutanol production. Lowering the temperature of the fermentation culture of step (d) occurs at a predetermined time. Lowering of the temperature of the fermentation culture of step (d) coincides with a change in a metabolic parameter, where the change in metabolic parameter is a decrease in the rate of isobutanol production. The first temperature is 25-40 degrees C. The second temperature is 3-25 degrees C lower than the first temperature. Steps (d) and (e) are repeated one or more times. The recombinant microbial production host is Clostridium, Zymomonas, Escherichia, Salmonella, Rhodococcus, Pseudomonas, Bacillus, Lactobacillus, Enterococcus, Alcaligenes, Klebsiella, Paenibacillus, Arthrobacter, Corynebacterium, Brevibacterium, Saccharomyces, or Pichia. The recombinant microbial host cell comprises at least one DNA molecule encoding a polypeptide that catalyzes a substrate to product conversion selected from (i) pyruvate to acetolactate, (ii) acetolactate to 2,3-dihydroxyisovalerate, (iii) 2,3-dihydroxyisovalerate to alpha -ketoisovalerate, (iv) alpha -ketoisovalerate to isobutyraldehyde, and (v) isobutyraldehyde to isobutanol; where the at least one DNA molecule is heterologous to the microbial production host cell. The polypeptide that catalyzes a substrate to product conversion of pyruvate to acetolactate is acetolactate synthase. The polypeptide that catalyzes a substrate to product conversion of acetolactate to 2,3-dihydroxyisovalerate is acetohydroxy acid isomeroreductase. The polypeptide that catalyzes a substrate to product conversion of 2,3-dihydroxyisovalerate to alpha -ketoisovalerate is acetohydroxy acid dehydratase. The polypeptide that catalyzes a substrate to product conversion of alpha -ketoisovalerate to isobutyraldehyde is branched-chain alpha -keto acid decarboxylase. The polypeptide that catalyzes a substrate to product conversion of isobutyraldehyde to isobutanol is branched-chain alcohol dehydrogenase. The acetolactate synthase has an amino acid sequence having at least 95% identity to a defined sequence of 559, 571, or 554 amino acids (SEQ ID NO: 2, 178, or 180), given in the specification, based on the Clustal W method of alignment using the default parameters of GAP PENALTY 10, GAP LENGTH PENALTY 0.1, and Gonnet 250 series of protein weight matrix. The acetohydroxy acid isomeroreductase has an amino acid sequence having at least 95% identity to a defined sequence of 395, 330, or 342 amino acids (SEQ ID NO: 181, 183, or 185), given in the specification, based on the Clustal W method of alignment using the default parameters of GAP PENALTY 10, GAP LENGTH PENALTY 0.1, and Gonnet 250 series of protein weight matrix. The acetohydroxy acid dehydratase has an amino acid sequence having at least 95% identity to a defined sequence of 616, 585, 550, or 558 amino acids (SEQ ID NO: 6, 186, 188, or 190), given in the specification, based on the Clustal W method of alignment using the default parameters of GAP PENALTY 10, GAP LENGTH PENALTY 0.1, and Gonnet 250 series of protein weight matrix. The branched chain alpha -keto acid decarboxylase has an amino acid sequence having at least 95% identity to a defined sequence of 548, 547, 550, or 554 amino acids (SEQ ID NO: 8, 193, 195, or 197), given in the specification, based on the Clustal W method of alignment using the default parameters of GAP PENALTY 10, GAP LENGTH PENALTY 0.1, and Gonnet 250 series of protein weight matrix. The branched chain alcohol dehydrogenase has an amino acid sequence having at least 95% identity to a defined sequence of 387, 312, 360, 389, or 390 amino acids (SEQ ID NO: 10, 199, 201, 203, or 204), given in the specification, based on the Clustal W method of alignment using the default parameters of GAP PENALTY 10, GAP LENGTH PENALTY 0.1, and Gonnet 250 series of protein weight matrix. EXAMPLE - No suitable example given.