"Reported TCA thresholds in wine are typically in the range of 2 ng/L for detecting a noticeable difference and 6 ng/L for true recognition. TCA levels below the 2 ng/L difference threshold can still impact a wine, usually described as "muted" aromas and flavors."
- ETS Labs' website
Is it random? Yes. TCA is a randomly occurring, systemic issue within the bark of the tree. Once isolated, that tree will be excluded from the beverage end of the cork business.
The process now involves screening bark, traceable to the trees. Classification and processing of the bark has become a stricter culling process over recent years. And the processes for treating the corks to ensure their reliability have improved as well.
Cork is still safer, greener, and better performing than ever before.
Read more here.