The seven factors we track, in detail. Each one shows up on every brand and category page.
Congeners
Byproducts of fermentation (methanol, acetaldehyde, fusel alcohols). Strongly linked to hangover severity; darker, less-distilled spirits carry more.
Non-ethanol volatile compounds produced during fermentation and distillation. Includes methanol, acetone, acetaldehyde, fusel alcohols (n-propanol, isobutanol, amyl alcohols), esters, and aldehydes. Multiple human studies link higher congener content to more severe hangover symptoms at equivalent ethanol doses. Bourbon has roughly 37× the congener content of vodka by some measures.
Histamines
Produced by bacteria during fermentation/aging. Trigger flushing, headaches, congestion in sensitive drinkers. High in red wine, beer, aged spirits.
Biogenic amines formed by decarboxylation of histidine by bacteria during fermentation, aging, and malolactic conversion. Triggers vasodilation, headaches, sneezing, and skin flushing. Levels are highest in red wine, aged cheese, and fermented foods. Alcohol additionally inhibits diamine oxidase (DAO), the enzyme that clears histamine, which is why drinkers react more strongly than they would to dietary histamine alone.
Polyphenols
Plant compounds with antioxidant activity. Slightly protective at low doses but at high concentrations may worsen hangover via tannin/quercetin reactions.
A broad family of plant compounds including flavonoids, tannins, anthocyanins, and stilbenes (e.g. resveratrol). Have antioxidant activity at moderate doses but at high concentrations contribute to headache mechanisms — quercetin in red wine, for instance, can interfere with alcohol metabolism in the liver.
Sulfites
Preservatives (SO₂) added to wine and some beers. Common trigger of headaches, asthma, and allergic-type reactions.
Sulfur dioxide (SO₂) and related compounds added as preservatives. Wine in the EU must declare sulfites above 10 mg/L; US law requires the "Contains Sulfites" label above the same threshold. About 1% of the population is sulfite-sensitive, with reactions ranging from sinus congestion to asthma. Sweet white wines carry the highest sulfite doses.
Tannins
Astringent polyphenols from skins, seeds, barrels. Bind proteins, slow alcohol clearance, and aggravate dehydration-style symptoms.
Astringent polyphenols extracted from grape skins, stems, seeds, and oak barrels. Bind to salivary proteins (producing the "drying" mouth feel) and may slow alcohol clearance. Heavy in Cabernet, Malbec, Nebbiolo, aged red wine, and cask-aged spirits.
Sugar
Residual sugar amplifies hangover via blood-sugar swings and dehydration. Liqueurs and cocktails are the main offenders.
Residual fermentable sugars plus post-distillation dosage. Drives glycemic spikes and crashes that look like hangover symptoms. Liqueurs, cream products, sweet wines, and spiced rums carry the most. Many "smooth" spirits owe their character to undisclosed sugar dosage within regulatory limits.
Additives
Colorants, flavorings, glycerin, propylene glycol, sorbates. Cheap spirits and ready-to-drinks often hide these in trade-secret formulas.
Permitted post-distillation additions: glycerin (mouthfeel), caramel coloring (E150a–d), oak extract (boisé), propylene glycol (carrier), sorbates, citric acid. The Mexican CRT permits 1% additives in 100% agave tequila; US TTB permits up to 2.5% in distilled spirits without label disclosure. Bourbon and straight whiskey are the only categories that prohibit added ingredients beyond water.