In linking a subordinate clause and a main clause, a relative pronoun functions similarly to a subordinating conjunction. Unlike a conjunction, however, a relative pronoun does not simply mark the subordinate (relative) clause, but also plays the role of a noun within that clause.
The main ingredient in most vodkas is some kind of grain, such as wheat, corn or rye. Potatoes are another common base ingredient for vodka, according to About.com.
Once you have made potato vodka, you may flavor it with berries or any type of fruit you choose. You simply need to add a handful of berries or chopped up fruit with 250g of sugar by weight to a liter of vodka. Shake the bottle every day for a week and your vodka will have a lovely fruity flavor to it.