How Do Congeners in Alcohol Affect Hangovers?

It’s a morning-after mystery: you go out and have a few drinks, nothing too crazy or out of the ordinary, but then, out of nowhere, you wake up the next day with a killer hangover. If you’re wondering what’s up (and how to avoid this unpleasant surprise in the future), there are several suspects you need to know about — congeners. 

You may have heard of them, but what are congeners exactly? Well, for one thing, these sneaky compounds might be the secret culprits behind our hangover woes. Which types of alcoholic drinks have them, and how did they get there in the first place? And if we’re sensitive to congeners, what’s the best alcohol for no hangover effects? Or, if “no hangover” isn’t an option, what’s the alcohol with the least hangover-inducing properties? Let’s find out!

What Are Congeners?

Congeners, meaning “same kind,” are compounds in alcoholic beverages that add to the flavor and aroma of alcohol (and, yes, hangovers). They result from fermentation — the process by which yeast converts sugars into alcohol. Congeners are another byproduct of this reaction.

The amount of congeners depends on a few different factors:

• The type of sugars used. Every type of alcoholic drink (from “bathtub gin” to wine that comes with a 4-figure price tag) calls for two basic ingredients: yeast and a source of sugar for it to feast on. However, the menu options for that feast can range from the grapes used to produce wine to the apples used to make cider to the many types of honey that become mead to the grains that serve as the base for beer, whiskey, and some vodkas. All of these ingredients leave behind some unique leftovers after fermentation which contributes to the flavor profiles and congener levels of each.
• The yeast strain. According to a Microorganisms article titled “The Role of Yeasts in Fermentation Processes,” wines, beers, and ciders are usually made with the help of Saccharomyces cerevisiae strains, “the most common and commercially available” type of yeast. However, Schizosaccharomyces pombe is used in molasses fermentation to produce rum, while Kluyveromyces marxianus strains are more common when producing vodka, gin, and other “white spirits.”

Are All Congeners the Same?

Each type of congener is built a little differently, and there are actually lots of different types with different molecular structures:

• Esters. Esters form when organic acids react with alcohol. True to their elegant-sounding name, many have distinctive fruity or flowery smells, which makes them a popular ingredient in many perfumes, beverages, and cosmetics. (Just look at the label of any beauty product and you’re likely to see a bunch of “ester” cousins in the mix!)
• Ketones. Ketones are a bit less romantic. An organic compound characterized by a carbonyl group (carbon and oxygen atoms bonded together), ketones are present in alcohol products such as beer. The jury is out on exactly what they taste like — some say sweet, others say metallic, while some say ketones remind them of nail polish. The important thing to keep in mind, however, is that they can be toxic in large amounts and tend to contribute to hangovers (more on this later).
• Acids. Lots of different acids can appear as congeners. For example, acetic acid tends to add a sharp, vinegar-like flavor. Citric acid found in fruits is another common congener, as are lactic acid, malic acid, and tartaric acid. For the most part, acids are quite harmless.
• Alcohols. Yes, other alcohols can be congeners, too! And this is where we run into trouble. Methanol in particular can spell trouble when it shows up as a byproduct of fermentation. It’s toxic even in moderate amounts, and its metabolism can get pretty ugly. (It’s typically only found in home-distilled products, as commercial operations filter out the majority of methanol.)
• Aldehydes. Acetaldehyde and formaldehyde in particular are notorious for their toxicity and the role they play in hangovers. In fact, acetaldehyde is a normal byproduct of alcohol metabolism in the body and is one of the culprits behind that icky malaise we feel the day after drinking!

The “Congener Fingerprint”

The amount and types of congeners in alcohol types tends to be unique. In a way, congeners act as a particular drink’s molecular “fingerprint!” 

In fact, analysis of the congeners present in a particular drink has been used as part of the so-called “hip flask defense.” Originating in Germany, this defense is an assertion that the alcohol a defendant was intoxicated with at the time of arrest was consumed after an accident rather than before it (i.e., “When the accident happened, the booze was still in my hip flask — I didn’t drink it until later, I promise!”). 

Backing this claim up hinges on calculating blood alcohol levels and comparing the exact congener profile in the defendant’s system with that of the alleged drink in order to prove the timing and the type of alcohol consumed. Of course, there are several obvious holes in this type of defense. For one thing, just because our suspect had a gin and tonic 10 minutes after a crash didn’t mean they didn’t also throw one back half an hour before. Plus, if they consumed a mixture of different drinks — and let’s be honest, this isn’t such a stretch — there would be too many compounds in the “congener cocktail” to make sense of which ones corresponded to a particular drink.

Still, the fact that the “hip flask defense” exists at all is testament to the unique nature of a particular drink’s congener profile. But what does any of this have to do with hangovers?

The Role of Congeners in Hangovers

Hangovers — those unfortunate reminders of the night before — come with a characteristic set of symptoms, including headaches, nausea, shakiness, fatigue, and overall malaise (Ugh!). To find out more about the timeline of hangovers and what causes them, check out our blog The Science Behind Hangovers: Why They Last as Long as They Do.

So where do congeners come in? In general, the reason congeners make hangovers worse has to do with the fact that the body has to break down the congeners in addition to the alcohol. Both processes release toxic byproducts. However, since the liver can only do so much at a time, the result is a buildup of toxins that are partially responsible for those oh-so-familiar hangover symptoms.

Methanol Mayhem

According to a Current Drug Abuse Reviews article, methanol in particular is a congener that can wreak the most havoc on the body. Methanol metabolism releases formic acid and formaldehyde — two highly toxic byproducts that will continue to cause damage in our system even hours later.

Here’s the breakdown of methanol in various alcohol types, according to “Alcohol Congener Analysis and the Source of Alcohol: A Review”:

• Brandy: as much as 4,766 milligrams of methanol per liter.
• Rum: 3,633 milligrams per liter. 
• Vodka: 102 milligrams per liter.
• Beer: 27 milligrams of methanol per liter.

However, the authors also point out a crucial fact to keep in mind: while it may be true that brandy or rum has more congeners than vodka, the latter is still very high in alcohol content. And when it comes to the intensity of a hangover, the amount of alcohol we consume — no matter what the levels of congeners it may have — is what ultimately makes the biggest difference.

Likewise, while congeners may play a role in hangovers, they don't seem to affect the level of impairment we experience as a result of drinking. The authors mention that “safety-sensitive performance that was affected by alcohol intoxication the previous night (vigilance with reaction time; ataxia) was not differentially affected by bourbon versus vodka.”

Ranking Congeners: Which Drinks Have the Most?

That said, if we’re sensitive to congeners, we might want to know exactly which types of alcohol have the most. 

The following have the highest levels of congeners:

• Dark liquors, such as whiskey and rum. Bourbon whiskey takes the prize for the most congeners of all. According to a Journal of Food Composition and Analysis article, “Bourbon whiskeys contain hundreds of congeners that determine flavor.” (This particular article identified 17, with the previously mentioned methanol being of most concern).
• Tequila. This one is a bit of a surprise. Even in the case of clear (blanco) varieties, tequila is on par with dark liquors as far as congeners are concerned.
• Red wine and cognac. Why do red wines end up with higher levels of congeners than their lighter counterparts? The reason has to do with warmer temperatures during fermentation, oak aging, and exposure to air. Oak aging in particular tends to be the biggest culprit, since it adds acetaldehydes to the mix.

The following alcohol types rank somewhere in the middle:

• White wine. While not congener-free, white wines have significantly lower levels of congeners than red wines, making them less likely to contribute to hangovers.
• Gin. This liquor is more hangover-friendly than its darker cousins but a bit less so than vodka.

These are the “winners,” as far as “least hangover-inducing” alcohol types are concerned:

• Vodka and sake. These clear spirits have very few congeners. But beware! As we mentioned earlier, they’re still very high in alcohol by volume (ABV), which means a hangover could be on the horizon if we go overboard.
• Beer. While beer does have some congeners, its relatively low ABV makes it the best option for avoiding hangovers. Still, moderation is key — it’s definitely possible to overdo it! Plus, all those empty calories really do add up, and “beer belly” is a real thing.

Tips for Avoiding Hangovers

So what can you do to stay smart about congeners and lower your chances of ending up with a nasty hangover? Here are some ideas:

• Stay on the light side. If you’re sensitive to congeners, stay away from darker liquors (such as rum) and red wines.
• Remember that congeners are only one part of the picture. Ultimately, it’s the alcohol content that matters most when it comes to hangovers.
• Keep an open mind. If you find yourself nursing a hangover more frequently than you’d like, it might be time to question your relationship with alcohol in general. Reframe can help you get started and support you as you gain momentum toward a healthier version of yourself!
• Explore your options. Track your drinking for a while and see if any patterns emerge. Then, experiment with setting limits or get sober-curious and see what lies beyond booze altogether! You never know — you may just find a new favorite mocktail or alcohol-free activity that’s way more fun (and doesn’t come with a hangover the next day).

Reframing as an Opportunity

In the end, it can be helpful to see a frustrating experience like a hangover (whether or not congeners are to blame) as an opportunity. It’s easy to go about our routine on autopilot and forget to listen to our own intuition — specifically, what our body is trying to tell us. Try to see the unpleasant effects as a sign that maybe it’s time to shift gears a bit and change up your weekend routine. Do this in the spirit of curiosity, not judgment — it’s an opportunity to discover what works best for you!