The objective of the research study was to identify chemical compounds that are impurities in ethanol obtained in the process of alcoholic fermentation of various maize varieties. There were described reasons for the formation of such compounds in the fermentation process of maize, which reduce the quality of ethanol produced. There was carried out a qualitative and quantitative identification of by-products in the spirits after the completed fermentation process was carried out. It included the following groups of compounds: esters, aldehydes, higher alcohols and methanol. The quality analysis of ethanol was performed using a gas chromatography method. The content of carbonyl compounds in the ethanol intended for food purposes is regulated by standards and cannot exceed the value of 0.1 g/dm³ of EtOH. In the samples analysed it ranged 0.022 ÷ 0.087 g/dm³ of EtOH. The highest amount of carbonyl compounds was found during the first stage of fermentation, when the highest quantities of ethanol were formed. During the subsequent hours of ethanol fermentation the amount of aldehydes gradually decreased, with the highest decrease observed between the 16th and 48th hour. In any of the spirits produced there was not found acrolein, which has carcinogenic properties. The amount of higher alcohols was within the fairly wide limits, i.e. 0.855 ÷ 3.553 g/dm³ of EtOH. Their level was impacted by the amount of n-propanol, isobutanol, n-butanol and 2-methyl-1-butanol. The yield of alcohol produced from 100 kg of grain of various maize varieties ranged 37.5 ÷ 43.3 dm³. The highest yield of spirit was reported in the case of the Euralis ES Runway and Euralis ES Hattric varieties.