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, corn husks, 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 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 selected from optical density, pH, respiratory quotient, fermentable carbon substrate utilization, carbon dioxide (CO2) production, and 2-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 2-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) pyruvate to alpha-acetolactate (pathway step a), (ii) alpha-acetolactate to acetoin (pathway step b), (iii) acetoin to 3-amino-2-butanol (pathway step c), (iv) 3-amino-2-butanol to 3-amino-2-butanol phosphate (pathway step d), (v) 3-amino-2-butanol phosphate to 2-butanone (pathway step e), and (vi) 2-butanone to 2-butanol (pathway step f), 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 alpha-acetolactate is acetolactate synthase. The polypeptide that catalyzes a substrate to product conversion of alpha-acetolactate to acetoin is acetolactate decarboxylase. The polypeptide that catalyzes a substrate to product conversion of acetoin to 3-amino-2-butanol is acetoin aminase. The polypeptide that catalyzes a substrate to product conversion of 3-amino-2-butanol to 3-amino-2-butanol phosphate is aminobutanol kinase. The polypeptide that catalyzes a substrate to product conversion of 3-amino-2-butanol phosphate to 2-butanone is aminobutanol phosphate phospho-lyase. The polypeptide that catalyzes a substrate to product conversion of 2-butanone to 2-butanol is butanol dehydrogenase. The acetolactate synthase has an amino acid sequence having at least 95% identity to a defined sequence of 559, 540, or 559 amino acids (SEQ ID NO: 4, 77, or 79), 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 acetolactate decarboxylase has an amino acid sequence having at least 95% identity to a defined sequence of 259, 255, or 259 amino acids (SEQ ID NO: 2, 81 or 83), 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 acetoin aminase has an amino acid sequence having at least 95% identity to a defined sequence of 453 amino acids (SEQ ID NO: 122), 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 aminobutanol kinase has an amino acid sequence having at least 95% identity to a defined sequence of (SEQ ID NO: 124), 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 aminobutanol phosphate phospho-lyase has an amino acid sequence having at least 95% identity to a defined sequence of 374 amino acids (SEQ ID NO: 126), 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 (SEQ ID NO: 14, 72, 75, or 91), 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 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 alpha-acetolactate (pathway step a), (ii) alpha-acetolactate to acetoin (pathway step b), (iii) acetoin to 2,3-butanediol (pathway step i), and (iv) 2,3-butanediol to 2-butanone (pathway step j), and (vi) 2-butanone to 2-butanol (pathway step f), 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 alpha-acetolactate is acetolactate synthase. The polypeptide that catalyzes a substrate to product conversion of alpha-acetolactate to acetoin is acetolactate decarboxylase. The polypeptide that catalyzes a substrate to product conversion of acetoin to 2,3-butanediol is butanediol dehydrogenase. The polypeptide that catalyzes a substrate to product conversion of 2,3butanediol to 2-butanone is diol dehydratase or glycerol dehydratase. The polypeptide that catalyzes a substrate to product conversion of 2-butanone to 2-butanol is butanol dehydrogenase. The butanediol dehydrogenase has an amino acid sequence having at least 95% identity to a defined sequence of 256, 350, 370 amino acids (SEQ ID NO: 6, 85, 87, or 89), 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 diol dehydratase or glycerol dehydratase comprises fused large, medium and small subunits and has at least 95% identity to an amino acid sequence comprising all three of the amino acid sequences encoding large, medium and small subunits, selected from (i) defined sequences of 554, 224, and 173 amino acids (SEQ ID NO: 8, 10, and 12), (ii) defined sequences of 554, 224, and 173 amino acids SEQ ID NO: 93, 95, and 97, (iii) defined sequences of 558, 230, and 173 amino acids (SEQ ID NO: 99, 101, and 103), (iv) defined sequences of 554, 228, and 174 amino acids (SEQ ID NO: 105, 107), and 109, (v) defined sequences of 554, 179, and 146 amino acids (SEQ ID NO: 135-137), (vi) defined sequences of 555, 196, and 141 amino acids (SEQ ID NO: 138-140), (vii) defined sequences of 555, 194, and 141 amino acids (SEQ ID NO: 146, 148, and 150), and (viii) defined sequences of 555, 194, and 142 amino acids (SEQ ID NO: 141-143), 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, where sequences are given in the specification. The butanol dehydrogenase has an amino acid sequence having at least 95% identity to a defined sequence of 346, 251, 387, 234 amino acids (SEQ ID NO: 14, 72, 75, or 91), 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.