892. Unfit Wine

Shabbos 29:15

Wine with a vinegar taste may not be used for kiddush even it smells like wine. Similarly, we may not recite kiddush over the water that was poured over the dregs of wine even though the resulting product tastes like wine. This is the case when the ratio of water and the resulting beverage is less than three to four; if the ratio is greater than three to four, it is considered diluted wine and kiddush may be recited over it.

Shabbos 29:16

If a person drinks from a vessel of wine, even if he only drinks a tiny bit from a vessel that contains many portions, he has invalidated the wine for sacramental purposes. One may not recite kiddush over the remaining wine, which is considered like the leftovers in a cup.