Tea Storage - Fresh For Less Than 3 Months?

by Julian

A 2008 study conducted by Purdue University found that green tea powders degrade significantly in 3 months at various humidity levels.

Bottled green tea beverages usually have acids added to them to preserve the stability of tea catechins, which is highly active and oxidise easily. However, things are different when green tea is in a powder form.

The researchers found that the presence of ascorbic acid or citric acid accelerate the degradation process. Samples of green tea powder alone and mixed with sucrose, citric acid, and/or ascorbic acid were prepared and stored in desiccators at 22 degrees C and 0-85% RH for up to 3 months.

Ascorbic acid is worst than citric acid. Both compounds were found to be bad for storage at greater than 58% and 75% humidity for citric and ascorbic acid respectively.

Catechins degraded the most in formulations containing both acids. Although catechin chemical stability was maintained at < or = 43% RH in all samples stored at 22 degrees C for 3 months, caking was observed in samples at these relative humidities

Does this result surprise me? Not at all. Similar results were published in Chinese studies that show that tea leaves stored at ambient will only keep fresh for about 3 months.

In other words, for the highest quality tea, you would expect vendors to freeze in sealed polyfoil packages. Doing anything less will cause catechins to react with oxygen and water molecules.

Perhaps another reason why green tea bags and instant powder mix offer poor value of money?

References

Ortiz J, Ferruzzi MG, Taylor LS, Mauer LJ (2008). Interaction of environmental moisture with powdered green tea formulations: effect on catechin chemical stability (). J Agric Food Chem. 2008 Jun 11;56(11):4068-77. Epub 2008 May 20. Department of Food Science, Purdue University, West Lafayette, IN 47907, USA.