Beer fault

Lore & Background

The article describes multiple specific beer faults, each with distinct causes and thresholds. Diacetyl, produced during fermentation and reabsorbed by yeast, causes a cream cheese mouthfeel if ambient temperature is below 26 °C (79 °F) and concentration exceeds 0.04 mg/liter. Acids from raw materials or yeast fermentation, when exceeding 170 mg/litre, produce a strong sour taste of yogurt or pepper. Octanoic acid (caprylic acid) above 4–6 mg/L gives a spicy taste, while butyric acid above 2–3 mg/litre tastes like metamorphic milk or rotten butter. Isovaleric acid, from oxidation of alpha acids, causes an odor at 0.7 to 1 mg per litre. Aldehydes like acetaldehyde cause green apple flavor above 5–15 mg/L. Phenols above 0.05-0.55 mg/L give bitter and smoky flavor. Hydrogen sulfide produces rotten egg flavor above 4 μg/L. Ferrous sulfate from metal contact causes rusty iron taste above 1.5 mg/L. Dimethyl sulfide creates sour-sweet cream flavor above 0.025 mg/L. Thiols (mercaptans) cause rotten vegetable flavors above 1 mg/L. Lightstruck causes sulfur taste from riboflavin and hop alpha acid reaction under light.

Reader's Guide

The article emphasizes that beer faults are significant because they directly impact the sensory quality of beer, making it unpalatable or undrinkable. Each fault has a defined chemical threshold and specific causes, often linked to temperature control, hygiene, oxygen exposure, and raw material quality. For example, diacetyl can be avoided by boiling the container and cleaning it before fermentation, and by raising temperature 2°-3° within 2 minutes of fermentation end to allow yeast reabsorption. Acid faults are reduced by hygienic production, mashing yeast strain for less than two hours, and keeping fermentation temperature below 50 °C (122 °F). Octanoic acid is controlled by storage below 26 °C (79 °F), using fresh yeast, and removing beer from yeast cake immediately. Butyric acid is avoided by keeping acidic sputum above 90 °F with minimal oxygen contact. Isovaleric acid requires clean environment and oxygen-free hop storage. Acetaldehyde prevention involves fresh yeast, hygienic environment, and high-sealing materials. Phenols are reduced by filtering tap water and using non-chlorine disinfectants. Hydrogen sulfide is reduced by healthy yeast and fully oxidized wort. Ferrous sulfate is prevented by using food-grade plastics and avoiding corrodible containers. Dimethyl sulfide is reduced by storing malt dry and boiling wort at high temperature for 60–90 minutes. Oxidation is minimized by keeping headspace less than one inch and storage below 50 °F (10 °C). Mercaptans are prevented by removing beer from yeast four weeks after fermentation start. The article notes that historically, inspectors had their own methods, such as testing sugar content by pouring beer on a chair and sitting to see if clothing stuck.

Did You Know?

• Diacetyl gives beer a mouthfeel similar to cream cheese when its concentration exceeds 0.04 mg/liter.
• Ferrous sulfate in beer above 1.5 mg/L can cause drinkers to develop symptoms of dizziness.
• Boiling wort at a high temperature for 60–90 minutes removes 90% of dimethyl sulfide.
• Historically, inspectors tested beer sugar content by pouring a small amount onto their chair and sitting to see if clothing stuck.