What to Know About Congeners in Alcohol

Medically Reviewed by Carol DerSarkissian, MD on February 15, 2024
3 min read

The central portion of an alcoholic drink is ethyl alcohol, or ethanol. But there are other compounds in alcohol, too. These are called congeners, and experts suggest that they may be the reason behind hangovers

Generally, dark alcohol or drinks darker in color have higher congener levels than alcoholic drinks that are lighter in color. 

During the distillation or fermentation process in alcohol manufacturing, the manufacturers also produce congeners. 

Yeast ferments sugars and converts them into alcohol. It does so by converting the amino acids in sugars into ethanol. Congeners are a by-product of this reaction. 

The amount of congeners in a drink depends on the carbohydrate used, the original sugar, and the yeast strain that ferments the sugar. Likewise, the amount of congeners in alcohol made using grapes or cereal grains also differs. 

Some congeners produced in the distillation process are: 

  • Esters
  • Ketones
  • Acids
  • Alcohols
  • Aldehydes 

These compounds are responsible for giving taste and aroma to the alcoholic drink. Thus, the congener amount in a drink gives it a particular taste profile.

For example, acetaldehyde is an aldehyde that gives rums and bourbons a fruity smell. Meanwhile, isobutylene alcohol is an alcohol that has a sweet smell. 

Clear alcoholic drinks, such as white wine, light rum, light beer, gin, and sake are low in congeners. As a rule of thumb, the lighter the drink, the lower the congener level because the drink is not heavily distilled. 

Tequila, cognac, and whiskey are drinks high in congeners. Bourbon whiskey has a substantial amount of congeners, more than most other alcoholic drinks. 

Drinking alcoholic drinks high in congeners can give you an intense hangover. For example, methanol is a congener that breaks down into formic acid and formaldehyde, worsening a hangover. 

Drinks high in congeners have a high amount of methanol. For instance, brandy has 4,766 milligrams of methanol per liter. Rum has 3,633 milligrams per liter. Vodka has 102 milligrams per liter. In comparison, beer contains just 27 milligrams of methanol per liter. 

Research shows that congeners may be responsible for causing a hangover, but they are not the only cause. 

The common belief is that hangovers are caused due to dehydration. However, congeners also impact the severity of the hangover.

In reality, though, people may drink a variety of alcoholic beverages with congeners of varying amounts. The hangover is the collective effect of these drinks. Although there is not enough research in this area, there is evidence that drinks with congeners in high concentration result in more severe hangovers. You need fewer drinks that are high in congeners to get a hangover.

The body has to break down all components of the alcoholic drink to recover from a hangover. A congeners hangover could occur if you drank a couple of high-congener drinks the night before. Since the body also needs to break down the congeners and ethanol, the hangover symptoms last longer. 

In a 2010 study, the researchers asked the study subjects to consume placebo, vodka, and bourbon. They were then asked about their hangovers. The participants who consumed bourbon had more severe hangovers as compared to the group that drank vodka. 

Thus, they concluded that high-congener drinks cause severe hangovers even when consumed in the same quantity as low-congener drinks. 

To avoid a hangover after a night of drinking with friends:

  • Limit your consumption of dark alcohol. Darker drinks have more congeners in them, causing a stronger and longer-lasting hangover. 
  • Instead of making your drinks at home, such as home-brewed beer, buy from the store. When you make beer at home, you do not have the same fermentation control as the manufacturer. So, homemade drinks tend to have high congener levels. 
  • Do not drink alcohol on an empty stomach, especially if it is high in congeners. A full stomach slows down alcohol absorption, giving the body more time to break down both congeners and ethanol. 
  • Drink water to hydrate yourself, alternating alcohol with water to prevent dehydration. The more dehydrated you are, the worse you will feel the following day. 

If possible, try to get adequate sleep after drinking a lot. It will help your body break down the compounds and make you feel much better.