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, or polysaccharides. The fermentation culture is maintained under conditions selected from anaerobic conditions and microaerobic conditions. While growing the production host of (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 selected from optical density, pH, respiratory quotient, fermentable carbon substrate utilization, carbon dioxide (CO2) production, and 1-butanol 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 1-butanol 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) acetyl-CoA to acetoacetyl-CoA, (ii) acetoacetyl-CoA to 3-hydroxybutyryl-CoA, (iii) 3-hydroxybutyryl-CoA to crotonyl-CoA, (iv) crotonyl-CoA to butyryl-CoA, (v) butyryl-CoA to butyraldehyde, and (vi) butyraldehyde to 1-butanol; 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 acetylCoA to acetoacetyl-CoA is acetyl-CoA acetyltransferase. The polypeptide that catalyzes a substrate to product conversion of acetoacetyl-CoA to 3-hydroxybutyryl-CoA is 3-hydroxybutyryl-CoA dehydrogenase. The polypeptide that catalyzes a substrate to product conversion of 3-hydroxybutyryl-CoA to crotonyl-CoA is crotonase. The polypeptide that catalyzes a substrate to product conversion of crotonyl-CoA to butyryl-CoA is butyryl-CoA dehydrogenase. The polypeptide that catalyzes a substrate to product conversion of butyryl-CoA to butyraldehyde is butyraldehyde dehydrogenase. The polypeptide that catalyzes a substrate to product conversion of butyraldehyde to 1-butanol is butanol dehydrogenase. The acetylCoA acetyltransferase has an amino acid sequence having at least 95% identity to a defined sequence of 392, 392, 394, 393, or 398 amino acids (SEQ ID NO: 2, 4, 129, 131, or 133), 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 3-hydroxybutyryl-CoA dehydrogenase has an amino acid sequence having at least 95% identity to a defined sequence of 282, 27, 284, or 246 amino acids (SEQ ID NO: 6, 135, 137, or 139), 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 crotonase has an amino acid sequence having at least 95% identity to a defined sequence of (SEQ ID NO: 8, 141, 143, or 145), 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 butyrylCoA dehydrogenase has an amino acid sequence having at least 95% identity to a defined sequence of 398, 539, 447, 447, or 398 amino acids (SEQ ID NO: 10, 147, 149, 151, or 187), 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 butyraldehyde dehydrogenase has an amino acid sequence having at least 95% identity to a defined sequence of 468, 862, or 468 amino acids (SEQ ID NO: 12, 153, or 189), 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 butanol dehydrogenase has an amino acid sequence having at least 95% identity to a defined sequence of 390, 389, 862, 387, or 477 amino acids (SEQ ID NO: 14, 16, 153, 155, or 157), 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.