White wines have a unique odor character due to viticulture, enology, and producer handling, but it is caused by the ratios of a small group of Key odorants. Riesling shares a few key odorants with other white wines but has a distinct and unmistakable personality. 1,1,6- Trimethyl-1,2-dihydroxnapthalene (TDN), a prevalent odor fault in Riesling wine, with a 'petrol' aroma when present over its threshold. TDN at sub-threshold levels is commonly regarded as critical to the impression of Riesling character. We explored how TDN concentration affects the recognition of Riesling wine character. We supplied Riesling-familiar individuals with 75ms puffs of 10mL Chardonnay headspace containing varying TDN concentrations, and they were compelled to choose "Riesling" or "not Riesling." The response probability was fitted to logistic models based on the molar content of TDN in Chardonnay. Separately, Riesling-familiar respondents were presented with the same Chardonnay-TDN samples but were asked "petrol" or "not-petrol". These findings were fitted to a logistic model, with the projected 0.5 likelihood of detecting "petrol" serving as the threshold for TDN in Chardonnay. The subjects exhibited similar but distinct thresholds for TDN perceived as "petrol" in Chardonnay wine, while all subjects responded positively to recognizing "Riesling" odor at TDN concentrations lower than the threshold for TDN in Chardonnay. Subjects recognize this mixture as "petrol" when TDN concentrations in Chardonnay wine are above the TDN threshold, a common flaw in Riesling wines. However, below the threshold, TDN produces a "silent note" (Xu and Firestein 2021) for Riesling identification.