If I had to guess, it would be because that's exactly the environment and process that consumers will use, so it would capture variables such as "what if the pr

If I had to guess, it would be because that's exactly the environment and process that consumers will use, so it would capture variables such as "what if the probiotic was out-competed by a bacteria living on your mug?" And then I would assume the sterile transfer was to preserve this state of the tea as-made without changing it on the way to the lab.