Can you drink grape juice in the 9 days ?
Grape juice is included in the prohibition not to drink wine during the nine days. Although the reason for not drinking wine is because it brings simcha, and because it was used in the Bais Hamikdash, and grape juice, which doesn’t have alcohol in it doesn’t bring simcha. Nevertheless, the prohibition includes anything that is even technically called wine. It is for this reason that people try using beer for havdalah for Shabbos Chazon, and don’t use grape juice.
Chayei Adam 133-16, M:B 551-61, Moadei Yishurun pg. 130 quoting R’ Moshe Feinstein zt”l