NOVELTY - High yield method (M1) of fermenting carbohydrate to ethanol in a fermentor, comprises: (a1) mixing a fermentation feedstock with a fermentation broth containing yeast and/or an enzyme; (b1) treating the mixture by adding a composition to the fermentor containing (a) 10-90 wt.% of an aldehyde, (b) 1-50 wt.% of a surfactant having an hydrophilic-lipophilic balance of 4-18, (c) 0-20 wt.% of an antimicrobial terpene or essential oils, (d) 1-50 wt.% of organic acids (comprising 1-24C fatty acids, or their salts, glycerides and esters) and (e) 1-50 wt.% of water; and (c1) isolating ethanol.    USE - The method is useful for fermenting carbohydrate to ethanol (claimed), which is useful as a biofuel.    ADVANTAGE - The method utilizes the composition that: provides high yield of ethanol; inhibits the development of antibiotic-resistant strains of bacteria (claimed); controls the formation of biofilms and destroys pre-existing biofilms in the fermentation system; reduces the antibiotic presence in the resulting sub-product of carbohydrates fermentation e.g. distilled grains, corn gluten and others; and improves yeast viability by decreasing the use of sulfuric acid and yeast prewash to decrease bacteria level.    DETAILED DESCRIPTION - High yield method (M1) of fermenting carbohydrate to ethanol in a fermentor, comprises: (a1) mixing a fermentation feedstock with a fermentation broth containing yeast and/or an enzyme; (b1) treating the mixture by adding a composition to the fermentor containing (a) 10-90 wt.% of an aldehyde (comprising formaldehyde, para-formaldehyde, glutaraldehyde and/or another antimicrobial aldehyde), (b) 1-50 wt.% of a surfactant having an hydrophilic-lipophilic balance of 4-18, (c) 0-20 wt.% of an antimicrobial terpene or essential oils, (d) 1-50 wt.% of organic acids (comprising 1-24C fatty acids, or their salts, glycerides and esters) and (e) 1-50 wt.% of water, where the concentration of aldehyde in the fermentor is 0.25-3 kg/MT of fermentation feedstock; and (c1) isolating ethanol. INDEPENDENT CLAIMS are also included for:    (1) a fermentation broth or slurry, comprising carbohydrate feedstock to be fermented, yeast and/or an enzyme, and a treatment composition containing (a)-(e) as above per se; and    (2) an improved method (M2) of fermenting carbohydrate to ethanol in a fermentor, comprising (a1)-(c1) as above per se, and (d2) collecting material remaining after fermentation and adding it to animal feed.