Fermentation begins as soon as yeast is added to the cooled wort. The concentrated wort is called malt extract. In addition to producing ethanol, fine particulate matter suspended in the wort settles during fermentation. It is a chamber between the brewing kettle and wort chiller. Oatmeal stout is one variety brewed using a percentage of oats for the wort. There is insufficient evidence to support the use of St. John's wort, valerian or passionflower. A lauter tun is the traditional vessel used for separation of the extracted wort. The primary phytochemical constituents of St John's wort are hyperforin and hypericin. Escitalopram should be taken with caution when using St. John's wort. Cytochrome P450 activators like St. John's Wort may decrease the activity of zolpidem. Venlafaxine should be taken with caution when using St John's wort. St. John's wort, turmeric, wheatgrass, and willow bark. Each run would produce a weaker wort and thus a weaker beer. Duration and pH variances also affect the sugar composition of the resulting wort. St John's wort may cause photosensitivity.