Unmalted wheat (30-40%), Pilsner malt and aged (surannes) hops (3 years) are used. The aged hops are used more for preservative effects than bitterness, and makes actual bitterness levels difficult to estimate. Traditional products use 10-30% fruit (25%, if cherry). Fruits traditionally used include tart cherries (with pits), raspberries or Muscat grapes. More recent examples include peaches, apricots or merlot grapes. Tart or acidic fruit is traditionally used as its purpose is not to sweeten the beer but to add a new dimension. Traditionally these beers are spontaneously fermented with naturally-occurring yeast and bacteria in predominately oaken barrels. Home-brewed and craft-brewed versions are more typically made with pure cultures of yeast commonly including Saccharomyces, Brettanomyces, Pediococcus and Lactobacillus in an attempt to recreate the effects of the dominant microbiota of Brussels and the surrounding countryside of the Senne River valley. Cultures taken from bottles are sometimes used but there is no simple way of knowing what organisms are still viable.