Higher Alcohols and Esters

Higher Alcohols

Higher alcohols contribute to beer flavor, but are also involved in ester formation. They have strong flavors, producing an “alcoholic” or “solvent-like” aroma, and can have a warming effect on the palate. Most higher alcohols are formed during primary fermentation.

There are 45 different alcohols identified in beer. They are named higher alcohols because thier molecular weight is greater than ethanol (C2H5OH).

There are two classes of higher alcohols: aliphatic (volatile and contribute hot, solvent, and alcoholic taste and smell), and aromatic (not volatile and can give beer “drinkability”).

Aliphatic Alcohols

Aliphatic alcohols are organic compounds with with open chains of carbon atoms volatile and contribute hot, solvent, and alcoholic taste and smell.

Examples of Aliphatic alcohols

n-propanol:
(CH3CH2CH2OH)

iso-amyl alcohol:
((CH3)2CHCH2CH2OH)

active amyl alcohol:
(C5H12O)

iso-butyl alcohol:
((CH3)2CHCH2OH)

Aromatic Alcohols

Aromatic alcohols are not volatile and are organic compounds containing one or more 6-carbon rings. They contain phenols (meaning they have a carboxyl group –OH bonded with aromatic hydrocarbon group) which are benzene based molecules.

Examples of Aromatic alcohols

2-phenylethanol:
(C6H5CH2CH2OH)

All higher alcohol production occurs during primary fermentation as byproducts of amino acid synthesis. Unlike Diacetyl, higher alcohols are not reabsorbed and reused by the yeast cell

Increased higher Alcohol factors: yeast strain, fermentation temperature, pitch rate, wort gravity, wort O2, wort FAN, fermentation vessel design.

Esters

Esters are formed by combining a higher alcohol with an organic acid. A organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are relatively stronger acids. Alcohols, with –OH, can act as acids but they are usually very weak.

Ester aromas

• ethyl acetate: solvent, nail polish
• isoamyl acetate: banana
• ethyl caproate: apple, aniseed
• ethyl caprylate: apple
• phenylethylacetate: roses