Sour beer

Sour beer is beer which has an intentionally acidic, tart or sour taste. The most common sour beer styles are Belgian: lambics, gueuze and Flanders red ale.

Brewing

At one time, all beers were sour to some degree. As pure yeast cultures were not available, the starter used from one batch to another usually contained some wild yeast and bacteria. Unlike modern brewing, which is done in a sterile environment to guard against the intrusion of wild yeast, sour beers are made by intentionally allowing wild yeast strains or bacteria into the brew. Traditionally, Belgian brewers allowed wild yeast to enter the brew naturally through the barrels or during the cooling of the wort in a coolship open to the outside air – an unpredictable process that many modern brewers avoid.

The most common agents used to intentionally sour beer are Lactobacillus, Brettanomyces, and Pediococcus. Another method for achieving a tart flavor is adding fruit during the aging process to spur a secondary fermentation or contribute microbes present on the fruit's skin.

Taste

Taste, gustatory perception, or gustation is the sensory impression of food or other substances on the tongue and is one of the five traditional senses.

Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on taste buds. Taste, along with smell (olfaction) and trigeminal nerve stimulation (registering texture, pain, and temperature), determines flavors of food or other substances. Humans have taste receptors on taste buds (gustatory calyculi) and other areas including the upper surface of the tongue and the epiglottis.

The tongue is covered with thousands of small bumps called papillae, which are visible to the naked eye. Within each papilla are hundreds of taste buds. The exception to this is the filiform papillae that do not contain taste buds. There are between 2000 and 5000 taste buds that are located on the back and front of the tongue. Others are located on the roof, sides and back of the mouth, and in the throat. Each taste bud contains 50 to 100 taste receptor cells.

Beer

Beer is the world's most widely consumed and likely the oldestalcoholic beverage; it is the third most popular drink overall, after water and tea. The production of beer is called brewing, which involves the fermentation of starches, mainly derived from cereal grains—most commonly malted barley, although wheat, maize (corn), and rice are widely used. Most beer is flavoured with hops, which add bitterness and act as a natural preservative, though other flavourings such as herbs or fruit may occasionally be included. The fermentation process causes a natural carbonation effect, although this is often removed during processing, and replaced with forced carbonation. Some of humanity's earliest known writings refer to the production and distribution of beer: the Code of Hammurabi included laws regulating beer and beer parlours, and "The Hymn to Ninkasi", a prayer to the Mesopotamian goddess of beer, served as both a prayer and as a method of remembering the recipe for beer in a culture with few literate people.