The Mission replies that the process of homebrewing, if not properly handled, will certainly produce harmful substances: 1, methanol Hydrolysis of pectin substances in grapes, amino acid deamination and fermentation of raw materials mold will cause a large number of methanol production. Barrel aging can reduce the content of methanol, but often do not have the conditions for homebrewing. Improper choice of yeast will produce more methanol, so it is recommended to buy special wine yeast. It is recommended to buy special wine yeasts. In addition, wines made at high temperatures generally have high levels of heterohydric oils. Finally, the addition of sugar will also produce heterohydric alcohols, because the sugar in the grapes is not the same as the type of sugar added, and the more sugar is added, the more heterohydric oils will be produced. 3, metal elements such as iron, on the one hand, grapes inevitably stained soil, which will contain iron. Another more important reason is the improper selection of appliances, and even some beginners use metal utensils homebrew, directly leading to the grapes were "killed".