Brew Chem 101: The Basics of Homebrewing Chemistry by Lee W. Janson Ph.d

Author:Lee W. Janson Ph.d.
Language: eng
Format: mobi
ISBN: 9780882669403
Publisher: Storey Publishing, LLC
Published: 1996-01-10T08:00:00+00:00

5. Understanding and Avoiding Off Flavors

Almost every step of homebrewing, from developing a recipe to bottling or kegging, can create some kind of off flavor. Unfortunately, even one off flavor can ruin an entire batch of beer. Despite this fact, one of the aspects of homebrewing least appreciated by homebrewers is an understanding of these off flavors, particularly where they come from and how they can be avoided in the future. Beginning brewing books often contain directions on how to avoid off flavors, but with no explanation why. The result is these critical actions are often glossed over and forgotten by the homebrewer. This chapter includes a thorough explanation of the causes of standard off flavors that often plague the unwary homebrewer and directions on how to avoid them.

ACETYLALDEHYDE

Off Flavor

Freshly cut, green apples and/or acetic-cider/rotten-apple smell and flavor.

Source

Acetylaldehyde is one of the chemicals along the normal chain of fermentation (see illustration, page 40). Normally acetylaldehyde will be processed to ethanol. However, in young beer or beer with a high alcohol content, this final conversion may not be completed—an effect especially evident when weak yeast is used—resulting in the smell and flavor of freshly cut, little green apples. Additionally, ethanol can be reversibly oxidized (see page 75) back to acetylaldehyde and acetic acid. The combination of the apple smell and the acetic acid give an “acetic-cider”/rotten-apple smell and taste. A third source of acetylaldehyde off flavor is bacterial infection, which creates a rotten-apple taste probably due to other bacteria-derived flavors.

To Avoid

Use good-quality yeast, especially when brewing high-alcohol beer styles. Allow beer to ferment and age for the proper amount of time. Eliminate bacterial infections by maintaining sterile brewing techniques.

ALCOHOLIC/SOLVENTLIKE

Off Flavor

Disagreeable alcohol flavor. Banana, rose, bitter, chemical (acetone or lacquer thinner), hot, or spicy flavors. Undesirable warming, prickly effect in the mouth and throat.

Source

The sweet flavor of ethanol, a two-carbon form of alcohol, is obviously desired in beer. Longer chain alcohols, including propanol (three carbons), butanol (four carbons), and related molecules are desired in limited quantities in high-alcohol beers like strong ales and barley wines or in certain beer styles such as bocks/double bocks. However, excessive amounts of these larger alcohol molecules, the so-called fusel alcohols (propanol, butanol, isobutanol, isoamyl alcohol) and phenolic alcohols (tyrosol), create a number of disagreeable off flavors, especially in lighter beer styles. Ethyl acetate, formed by the combination of ethanol and acetic acid, is often a major contributor to a solventlike off flavor.

MOLECULES CONTRIBUTING TO ALCOHOLIC SOLVENTLIKE OFF FLAVORS

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