The first stage of the wedding ceremony is "Kiddushin" or "Erusin," which begins with a Beracha recited by the Mesader Kiddushin (officiating Rabbi) over a cup of wine. If no wine or grape juice is available, then the Beracha may be recited over beer, in which case the Beracha of "She’hakol" is recited in place of "Ha’gefen." If no beer is available, then another alcoholic beverage, such as whiskey, may be used. If no such beverages are available, then the Kiddushin may be conducted without any beverage. Although it is customary to have a cup of wine under the Hupa, the wine (or other beverage) is not indispensable to the ceremony, and the Kiddushin may be performed without it.
The original practice was for the groom to recite the Birkat Erusin. Since he performs the Misva of getting married, he should be reciting the Beracha. However, the Rabbis enacted that the officiating Rabbi should make the Beracha, instead, because otherwise grooms who are unable to read and recite the Beracha would be embarrassed. In order not to make any groom feel ashamed, it was decided that the Meseder Kiddushin should always recite the Beracha. Therefore, since the Beracha fundamentally should be recited by the groom, the groom must listen attentively to the recitation and then answer "Amen." He should not answer "Baruch Hu U’baruch Shemo" during the Beracha, but should rather listen silently. The bride, too, should listen silently and attentively to the Beracha as the Rabbi recites it, because she also performs a Misva by getting married. Neither the bride nor the groom should be praying or whispering to each other while the Beracha is being recited.
Summary: If no wine or grape juice is available at the Hupa ceremony, beer or whiskey may be used. If even these beverages are not available, the ceremony may be performed without any beverage. The Hatan and Kalla must listen quietly and attentively as the Rabbi recites the Birkat Erusin, and then answer "Amen" to the Beracha.
