There are several Dunkin Donuts and Starbucks that advertise selling coffee with “Cholov Yisroel available upon request”. My question is as follows. If there is no mashgiach on premises, as long as there are no Jews able to see what’s going on behind the counter, what’s to prevent them from pouring Cholov Stam into the open Cholov Yisroel bottles? Would mirsas apply if it is so easy to make the switch when nobody is looking? I can imagine the scenario that they are running out of Cholov Yisroel and will want to accommodate the next wave of makpid customers. In particular, if they see that some frum Jews are not makpid, they may say to themselves, “What’s the big deal?” In some of these places you can’t even see what’s going on behind the counter. I don’t understand how it’s possible to call it Cholov Yisroel if it has lost its shmira. Let’s say they do have mirsas and we are not worried that they will switch the milk, wouldn’t the fact that it is not being watched by a Jew basically redefine the open bottles of milk as Cholov Stam? I have brought this up with friends numerous times but they all tell me that it’s different and they don’t think I have a good question. I can’t fathom why it would not be a question.
You are really asking a very good and basic question regarding any kosher food product left in the possession of a non Jew unattended where there is a possibility that he exchanged it for something non kosher. If the non Jew will not profit from the exchange, or he fears that he might get caught, or he might lose his reputation or job are all reasons to be lenient.
Y:D 118:7&10, Taz 10, Teshvas Mabit 1:208, Be’er Shevah 44, Chochmas Odom 70:8