Any practical questions should be brought to your local competent rabbinic authority. Here, I will merely attempt to show the relevant sources on this issue.

1) It does seem that the practice mentioned above is very questionable. I would have thought that this is considered as a Pikadon because one is putting the yogurt or cheese in a fridge which is used partially by Nochrim, who have ready access to the fridge, so it would be considered that the items have been entrusted with all of these workers.

2) If we accept that this is a Pikadon, then we learn in the Shulchan Aruch (Yoreh Deah 118:1) that if a Pikadon of milk was entrusted with a Nochri, one requires one seal to ensure that it has not been replaced with non-supervised milk. The Shach (#8) discusses why one seal is sufficient, since we know that milk from a non-Kosher animal is a Torah prohibition, and the Halachah is that one requires two seals to protect a Torah prohibition. To explain this, the Shach cites one of the Rishonim (the "Isur v'Heter") who says that nowadays most of the available milk is Kosher, so nowadays milk of Nochrim is a Rabbinic prohibition.

3) According to this, one would require one seal to protect the yogurt or cheese. One would have to close it in a way that it would be clearly recognizable if somebody had opened it.

Kol Tuv,

Dovid Bloom

I have looked further into this question and it seems that it may also be related to another Sugya that we have learned recently in the Dafyomi cycle.

1) The Gemara in Avodah Zarah (end of 11b and beginning of 12a) says, "Have you never in your life been to Sidon and seen a Yisrael and an Akum who placed two pots on one stove, but still the Chachamim are not concerned about this?" Rashi (12a, DH v'Lo) writes that even though forbidden foods are placed very near permitted foods, this is still in order. According to this, it would seem that one need not be concerned that the Kosher yogurt and non-Kosher yogurt, etc., are very near each other in the fridge.

2) However, there is a question on this from a different Gemara. In Chulin 112a, Rav Dimi asked Rav Nachman whether one may place a jar of salt next to a jar of Kutach (a milky concoction). Rashi explains that the question is are we worried that some of the milky Kutach will fall in the salt without one being aware of it, and one might salt meat with the milky salt. Rav Nachman replied that it is forbidden to place these two jars next to each other.

3) The Ran (Chulin 41a in the pages of the Rif, DH Garsi b'Gemara) asks how these two seemingly contradictory Gemaras can be reconciled. He answers that there is a distinction between something one does only occasionally and something that one does every day. The Kosher and non-Kosher items were not put near each other in Sidon on a regular basis, so Chazal were not concerned that they may get mixed, while storing salt next to milk on a regular day-to-day basis is more likely to lead to mixtures.

4) According to the Ran, storing the yogurt, etc., in the communal fridge on a regular basis would be a problem. Also, I suggest that the fridge scenario might be worse than the Sidon scenario, because being a communal fridge means that the Nochri has a share in the fridge, which is different from the Sidon example where the only issue involved was the closeness of the Kosher and non-Kosher foods. In contrast, the case of the fridge is comparible to giving a Pikadon to the Nochri, as I wrote in my first reply.

Kol Tuv,

Dovid Bloom