A certified restaurant will be hosting a wine tasting party at which they will serve samples of many wines including some which are not mevushal.¹  Non-mevushal wine becomes non-kosher if it is touched, moved or poured by a non-Jew,² and in order to prevent such an occurrence (and to avoid having to let certain people pour wine but not others), the only people who will be allowed to pour wine at this event will be cRc Mashgichim.

There are, however, other concerns which stem from the fact that as the non-Jew drinks from his glass of non-mevushal wine, he renders that drink non-kosher.  If he leaves some of this non-kosher wine in his glass, there are two possible ways this might affect other items in the restaurant, as follows:

1. If the wine goes into the dishwasher or sink used to wash kosher dishes, the ta’am of the non-kosher wine might affect the status of those dishes. 
2. If the Mashgiach refills the non-Jew’s cup, the kosher wine in the bottle will become non-kosher, as per the halacha of nitzuk chibur outlined below.

To avoid these concerns, the following measures will be taken at the wine tasting event:

• All glasses will be rinsed out at ambient temperature before they are washed.
• Wine will not be poured into cups which have already been used (i.e. there will be no refills).
• Mashgichim will pre-fill all of the sample cups before attendees ask for a drink, such that the guests can take drinks by themselves and will have no reason to approach the Mashgiach for a drink.

Nitzuk Chibur

If there is kosher wine³ in a bottle, for example, and non-kosher wine in a cup, and someone pours wine from the bottle into the cup, the liquid connection between the bottle and cup forces us to consider the situation as if the wine in the bottle and cup are thoroughly mixed together.⁴  Therefore, even if the person stops pouring the wine, the wine that remains in the bottle is viewed as being a mixture of kosher and non-kosher wine (and forbidden) even though there is physically no non-kosher wine mixed in the bottle.⁵

This halacha, known as nitzuk chibur (lit. “pouring establishes a connection”) is specific to wine which is assur b’hana’ah.⁶  One might therefore think that nitzuk chibur would not apply nowadays to stam yayin because (many hold that) wine is not assur b’hana’ah.  Shach 126:9 raises this point and rejects it, ruling that nitzuk chibur does apply even to stam yayin nowadays, and this opinion is accepted by Chochmas Adam and Chazon Ish.⁷

Accordingly, if a non-Jew drinks from a glass of non-mevushal wine that wine is forbidden as stam yayin, and if someone pours kosher wine into the residue of that drink, the residue is considered to have been mixed into the bottle of wine.  [If this inadvertently occurred and the bottle has 60 times the volume of the non-kosher wine residue, the non-kosher wine would be batel and the bottle of wine would be permitted b’dieved.]⁸