Contamination
Japanese: コンタミネーション（汚染）
The unintended introduction of extraneous microorganisms. It can compromise the quality of fermented foods and is prevented through hygiene management and environmental control.
Contamination—'kontami' for short—is one of the most feared events in fermentation. It refers to unintended microorganisms infiltrating and disrupting the fermentation process.
If containers for miso-making are not properly sanitized, contaminant bacteria can multiply and cause off-odors. If natto bacteria are brought into a sake brewery, koji fermentation may be disrupted.
Yet complete sterility is not always necessary. In nuka beds and wooden barrel brewing, the coexistence of diverse microbes actually creates flavor complexity. Neither fearing contamination too much nor neglecting control—finding that balance is part of what makes fermentation fascinating.