Making homemade wine isn't dangerous in the life-or-death sense, unlike making moonshine, where a mistake can cause blindness. The wine-making process creates an environment inhospitable to bacteria that could cause sickness. Still, there are still things that can go wrong to ruin a batch of wine, the majority of which are sanitation issues.
One of the most common complaints from homemade wine is that it causes headaches the next day. Headaches are caused by an overabundance of tannins and histamines in the wine. Tannins are most prevalent in red wine, and getting a proper balance requires experience.
Everything that comes into contact with the wine must be completely sterilized, even your hands. Any addition of a contaminant or bacteria will greatly affect the taste of the wine. The tiniest amount of bacteria could make your wine smell and taste like vinegar. When bacteria comes into contact with wine and oxygen, it produces acetic acid, which ruins wine.
Racking is the process of siphoning the clear liquid from the sediment (lees) at the bottom of the barrel or container and transferring the liquid into new storage. As with any other aspect of wine making, everything has to be clean. Another thing to keep in mind is timing. If the juice is allowed to sit with the lees too long, it will create a musty flavor and smell because of the dead yeast.
It is important to use food-grade containers at all stages of the wine-making process. Plastics, copper, iron and other materials that are not food-grade can taint the color and flavor of wine. An isolated incident provides a prime example for the necessity of quality materials. A man in Australia was hospitalized with severe lead poisoning caused by storing crushed grapes and juice in a corroded enamel bathtub before bottling.
Barrels, bottles, corks, tubes and other tools should be sterilized. The most common method is to dissolve 2 ounces of potassium metabisulphite into a gallon jug of water and rinse everything that will come into contact with the wine. After rinsing with the solution, everything should be rinsed again with cold water. The potassium solution will keep for six months if sealed tightly. Bottles should be boiled and rinsed multiple times to rid them of sediment, bacteria and oxidization.