Beer quality faults — What defect can contamination by “S. patorianns” (intended: wild <em>Saccharomyces</em> pastorianus or related yeast) cause in finished beer?

Introduction / Context:
Beer clarity is a key quality attribute. Besides colloidal haze from proteins and polyphenols, microbial contamination by wild yeasts can cause turbidity, over-attenuation, and package overpressure. The name “S. patorianns” in older question banks refers to wild Saccharomyces species such as S. pastorianus (S. carlsbergensis) that may appear as contaminants when process controls fail.

Given Data / Assumptions:

• Context: finished beer after filtration/pasteurization intended to be stable.
• Contaminant: wild Saccharomyces capable of growth in packaged beer.
• Symptom focus: observable defect in the product.

Concept / Approach:
Wild yeast growth in packaged beer increases cell counts leading to visible turbidity and sometimes sediment. Flavor faults (esters, bitterness, astringency) can change, but the most immediate and consistent sign is cloudiness due to suspended yeast. Therefore, among the listed choices, turbidity (cloudiness) is the characteristic defect to select.

Step-by-Step Solution:

Verification / Alternative check:
Quality control workflows include membrane filtration and selective media to detect wild yeasts precisely because they generate turbidity and refermentation in pack.

Why Other Options Are Wrong:

• Ester-like taste: can be influenced by yeast metabolism, but haze is a clearer, primary indicator.
• Stringent (astringent) taste: more tied to polyphenols/tannins from malt/hops or process issues.
• Bitter taste: largely from iso-alpha acids; not a hallmark of wild yeast contamination.

Common Pitfalls:
Confusing protein–polyphenol haze with microbial haze; microbiological testing differentiates the causes.

Final Answer:
cloudiness in beer