flat sour: meaning, definition, pronunciation and examples
Low/Very LowTechnical/Industrial
Quick answer
What does “flat sour” mean?
A type of spoilage in canned or preserved foods, especially low-acid vegetables, caused by heat-resistant bacteria (Bacillus coagulans and related species) that produce acid without gas, resulting in a sour taste and often a flat, unpressurized container.
Audio
Pronunciation
Definition
Meaning and Definition
A type of spoilage in canned or preserved foods, especially low-acid vegetables, caused by heat-resistant bacteria (Bacillus coagulans and related species) that produce acid without gas, resulting in a sour taste and often a flat, unpressurized container.
In a broader food industry context, it can refer to any sour taste defect in preserved products where fermentation occurs without gas production, leading to loss of carbonation in beverages or spoilage in other packaged goods. It can also be used metaphorically to describe something that fails to meet expectations in a disappointingly bland or sour way.
Dialectal Variation
British vs American Usage
Differences
No significant dialectal differences in meaning or usage. The term is standard international technical jargon in the food industry.
Connotations
Purely technical and negative, denoting a specific failure in food preservation.
Frequency
Equally low frequency in both varieties, confined to professional/technical domains.
Grammar
How to Use “flat sour” in a Sentence
The [canned food] developed/had/suffered from flat sour.To prevent/avoid/cause flat sour.Vocabulary
Collocations
Examples
Examples of “flat sour” in a Sentence
verb
British English
- The batch of canned peas had been flat-soured by the contamination.
- Improper cooling can cause the product to flat sour.
American English
- The corn flat-soured due to insufficient processing.
- They were worried the new line would flat sour.
adverb
British English
- (Not standard; no common adverbial use.)
American English
- (Not standard; no common adverbial use.)
adjective
British English
- They identified a flat-sour defect in the tinned carrots.
- The flat-sour spoilage was traced back to the filler.
American English
- The lab confirmed it was a flat-sour contamination.
- Flat-sour cans are often indistinguishable from good ones by sight.
Usage
Meaning in Context
Business
Used in quality assurance reports, supplier audits, and production loss analyses in the food manufacturing sector.
Academic
Found in food microbiology textbooks, journal articles on thermal processing and food preservation.
Everyday
Virtually never used in everyday conversation.
Technical
Core term in food technology, thermal processing engineering, and industrial microbiology for canned foods.
Vocabulary
Synonyms of “flat sour”
Strong
Neutral
Weak
Vocabulary
Antonyms of “flat sour”
Watch out
Common Mistakes When Using “flat sour”
- Using it as an adjective phrase for a person's mood (e.g., 'He felt flat sour').
- Confusing it with 'swell' or 'blown' cans where gas is produced.
- Pronouncing it as a single stressed unit instead of a compound with near-equal stress.
FAQ
Frequently Asked Questions
Flat sour spoilage itself is not typically associated with food-poisoning toxins, but the food is spoiled, sour-tasting, and unfit for consumption. Other, more dangerous bacteria could be present, so it should not be eaten.
Yes, it is a risk in home canning of low-acid vegetables (like beans, corn, peas) if proper pressure canning procedures and times are not followed to destroy the heat-resistant spores.
Visually, the can will look normal (not swollen). The defect is only discovered upon opening and tasting the sour, often fermented-smelling contents.
The primary cause is insufficient thermal processing (time/temperature) during canning, which fails to destroy the spores of thermophilic (heat-loving) acid-producing bacteria like Bacillus coagulans.
A type of spoilage in canned or preserved foods, especially low-acid vegetables, caused by heat-resistant bacteria (Bacillus coagulans and related species) that produce acid without gas, resulting in a sour taste and often a flat, unpressurized container.
Flat sour is usually technical/industrial in register.
Flat sour: in British English it is pronounced /ˌflat ˈsaʊə/, and in American English it is pronounced /ˌflæt ˈsaʊɚ/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “[Metaphorical, rare] 'The party was a flat sour affair.' (disappointingly dull and unpleasant)”
Learning
Memory Aids
Mnemonic
Think of a can of sour vegetables that should be fizzy from spoilage gas but is FLAT instead. FLAT (no bulge) + SOUR (taste) = the spoilage type.
Conceptual Metaphor
FAILURE IS SOURNESS / A LACK OF EXPECTED PRESSURE IS FLATNESS.
Practice
Quiz
In which industry is the term 'flat sour' primarily used?