The content of diacetyl is the decisive index to measure whether the beer flavor got matured. Its content above the taste threshold value in beer would result in unpleasant sour beer taste.

双乙酰是衡量啤酒风味成熟与否的决定性指标，其含量超过其味阈值，会给啤酒带来不愉快的馊饭味，影响啤酒风味。

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To prove that MTBE concentrations below the EPA's threshold still made water taste terrible, Summy unearthed documents like a 1983 Shell letter detailing that water was no longer drinkable where MTBE'S concentration was 7 to 15 parts per billion.

FORBES: Demonizing for Dollars