Many people notice they don’t feel well after drinking cheaper wines. In fairness there are well-made wines that are inexpensive, though it is more common to see practices that contribute to wine headaches in “cheap” wines. The problems that these wines cause people come from using alternatives to oak barrels, adding sugar to increase the alcohol content, and not controlling fermentation to control the congeners produced during fermentation.
Congeners are the substances besides alcohol that are produced from fermentation. They include fusel oils, methanol, acetone, acetaldehyde, tannins, and aldehydes. Many congeners produce the accents in wine that we treasure; these “good” congeners are fusel oils and tannins. The others (methanol, acetone, acetaldehyde, and aldehyde) are much harsher tasting, take away from the flavor of wine and are hard for us to metabolize and eliminate.
The oak barrel alternatives are chunks, chips, sticks, powder, cubes and staves of oak used in steel tanks. Many very good wines are made this way, however, many very crude, inexpensive wines are made in this way, as well. Oak barrel alternatives, when used without finesse, can produce wines that are too heavy in tannins for those who are sensitive to them.