Several years ago, I went on a tour of the Celestial Seasonings tea factory in Boulder, Colorado.  The guide showed us the bales of tea as they arrived, machines that ground and mixed the tea, and a machine that put the tea in tea bags.  The tour included a visit to the room where the peppermint tea was stored.  Our guide told us that peppermint was stored separately so that it would not contaminate the other teas.  He did not tell us what was to come.