Sour beers are at a ninety degree angle to most conventional beers in that food spoilage organisms are deliberately added to beer to produce sourness & other tastes & aromas described as barnyard, horse blanket, leathery & butterscotch. Sometimes it's just the acidic sourness that is required as in a Berliner Weisse & othertimes it's about the less immediately appealing flavours mentioned above like in a Lambic beer.
Popular Styles of Sour Beer
Berliner Weisse – a clean-tasting, relatively low alcohol (about 3%), acidic, sour wheat beer. Lactobacillus is the microorganism that provides the sourness.
Lambic – acidic with barnyard aromas & flavours, aged hops (less hop character, more cheesey), spontaneously fermented rather than a specifically cultured souring microorganism being added.
Gueuze – aged lambics are blended with a younger one before packaging to give the souring yeasts some food & in turn carbonate the beer.
Fruit Lambic – fruit (tradtionally cherries or Rasberries to make a Kriek or Framboisen) are added to Lambic beer to offset some of the sourness with the sweetness of the fruit.
Flanders Red Ale – long maturation in oak barrels is important to this beer as Lactobacillus in the wood sours the traditionally fermented beer. The red colour comes from Vienna or Munich malts.
Flanders Brown Ale – similar to Red Ale, but from darker malts.
Traditionally sour beers got the wild yeasts & bacteria from the natural environment around the brewery by opening the doors & windows for the breeze to send microorganisms through the brewery into the cooling wort. The variation in microorganisms throughout the year means that each batch is different & blending several batches achieves some consistency. Barreling beer in wooden casks is a way to innoculate it with souring agents as wood is very difficult to sanitise & the bugs from the wine or beer previously in the barrel will infect the beer - in fact even beers naturally left open to the atmosphere for wild bugs to infect will get most of their desired characteristics from the barrel it is matured in. A more modern bewery may culture a specific blend of souring microorganisms to acheive a more consistent product.
Bacteria – Pediococcus (lactic acid producing bacteria ), Lactobacillus (lactic acid producing bacteria) Varieties used to ferment cabbage into sauerkraut, other varieties gives the diacetyl butterscotch flavour to Chardonnay wine & still others in cheese & yoghurt.
- Acetobacter (acetic acid producing bacteria) is used commercially to make vinegar.
Regular Saccaromyces Cerevisiae brewers yeast is often used to ferment the wort with the souring bugs finishing the beer in the packaged product.
In the lactic acid pathway, a 6-carbon sugar such as glucose is convert it into 2 units of lactic acid releasing stored energy in the process for the living cell to use.
C6H12O6 —► 2 ( C3H6O3 )
Glucose —► Lactic Acid
C6H12O6 —► C2H6O + 2 (CO2) —► +O2 —► C2H4O2
Glucose —► Ethanol + Carbon Dioxide —► + Oxygen —► Acetic Acid
Other metabolites from the microorganisms produce the flavours sought out by many beer enthusiasts but are produced in tiny amounts. The sensitivity of the human palate for them is very low, so show up proportionally more than the acids above.