Determining Error Rate in Titratable Acidity Testing
Dr. Patricia Howe
VWA Ask the Experts Webinar
On April 2, 2024, Dr. Patricia Howe taught a webinar titled "Error Rate in Titratable Acidity" as part of the Virginia Wineries Association Ask the Experts series.
In this webinar, Dr. Howe invited attendees to embark on a thought experiment exploring the variation in values that might be obtained when testing titratable acidity in juice and wine. Dr. Howe highlighted several different aspects of variation that might occur, as well as offering practical solutions to obtaining more accurate and precise results. Principles presented here are also applicable to other analyses commonly performed in the winery laboratory.
Take-home messages:
- Lab techniques have known levels of variation outside “human error”, simply due to the standardization of solutions and variation in measuring devices. Based on these variations, it is possible to predict the variation in results that might be expected. For example, in the worst case scenario (inaccurate measuring devices, poorly standardized solution), the titratable acidity measurement of a juice with TA of 7.5 g/L may vary from 6.6 g/L to 8.4 g/L. Luckily, the range of values is distributed in a bell-shaped curve, so the probability of seeing this wide a range is low. Dr. Howe gives examples of how to improve this range.
- Titratable acidity is relatively stable in finished wine, so a box wine can be used as a standard. Select a wine with a titratable acidity in the range of your usual samples and have it tested at a trusted service lab. Run a sample of the box wine each time you set up for TA analysis to ensure you are within an acceptable range of the known value.
- Track your results for the standard over time to determine the true range of error in your own lab. If that range is too wide, consider investing in better measuring devices (see #1).
