Expert Review Panel for Kombucha Tea

2. Does the method contain system suitability tests or controls as specified by the SMPR? If not, please indicate if there is a need for such tests or controls and which ones. * A number of controls were provided. Method performance results for linearity, LOQ, accuracy and precision were provided. Reference chromatograms and spectral data was not included.

3. Is there information demonstrating that the method system suitability tests and controls as specified in the SMPR worked appropriately and as expected? If no, please specify. * Yes

4. Based on the supporting information, is the method written clearly and concisely? If no, please specify the needed revisions. * The method was written clearly and concisely.

5. Based on the supporting information, what are the pros/strengths of the method? * The method is highly sensitive and selective for ethanol. It also uses modern technology to reduce the chances for matrix interference. It also uses a constant dilution factor within the analytical range, and deuterated ethanol internal standards, to be able to separately distinguish the internal standard from naturally occurring ethanol.

6. Based on the supporting information, what are the cons/weaknesses of the method? * As mentioned, the repeatability study was done in a low-alcohol kombucha matrix spiked with a known amount of ethanol. The precision results from this study were excellent. No formal repeatability was done on higher kombucha samples. Regardless of alcohol content, a case can be made that one sample from one manufacturer does not reflect the diversity of manufacturing processes used for kombucha. Consequently, higher imprecision was observed in the naturally high alcohol commercial samples, with the percent difference of duplicates being greater than 4% for 6 of 13 samples, and greater than 10% for 2 of these. Repeatability RSD was not performed on other kombucha samples that contained higher amounts of alcohol, without spiking. If a high alcohol kombucha was included in the repeatability analysis, it would be easier to rule out the potential interferences that may not be accounted for by spiking a low alcohol kombucha. The method could also have provided additional system suitability parameters such as reference chromatograms or spectral data for quality control purposes. One complaint often made by traditionalists of alcohol analysis is the cost and expertise required for newer and more advanced methods, of which is this one example. However, the robustness of the method, expertise require and the analysis time should be balanced against cost.