Beer is a fermentation product. Yeast turns sugars into alcohol and carbon dioxide while the other components give flavour to the beer. The most common type of yeast is the Saccharomyces cerevisiae and is used all sorts of processes from baking to brewing and other things. It’s one of the most intensively studied micro-organisms. Researchers have mapped its entire genome and thus it can be genetically modified to the specific requirements of any process.
There are three main types of fermentation being top-, bottom- and spontaneous fermentation. Lagers and other common types of beers use bottom fermentation where the yeast sinks to the bottom of the fermenter and takes place at a low temperature (7-13°C).
Spontaneous fermentation is the process where mother nature takes over. The beer is inoculated with a wild-type yeast rather than a specifically cultivated type of yeast. The final product is thus not determined by the brewer. The flavours are sometimes buffered in case it gets too acidic. A famous example of this type of beer is Lambic.
Ales and some stouts will use top fermentation. Top fermentation lets the yeast form a thick foamy head on top of the fermenter and is carried out at higher temperatures. This makes the process shorter. Top fermentation is often carried out in open vessels. This causes a greater risk for infection but with the right safety measures this shouldn’t cause a problem.
The biggest difference between the these types of fermentations is whether the beer is ‘alive’ or not. Lagers and other beers that are brewery-conditioned are chilled after the fermentation process, have their yeast removed and are pasteurised to make it sterile. They’re also force-carbonated while being tapped or bottled.
Ales don’t go through this process which is why they’re referred to as ‘alive’ or ‘real ales’ as they contain living organisms in their final product. The yeast in the final product gives the beer its finishing touch and maturity as it ferments the leftover sugars and carbonates the bottled product, this is called secondary fermentation. This causes the beer to have a shorter shelf-life than other types of beer and need to be taken care of during storage at home or in pubs.
When I spent my days in Ireland I visited the Smithwick’s ale brewery in Kilkenny. I got to sample a lovely pint of Smithwick’s red-ale and in my opinion it’s one of the best classic ales. So for anyone wondering what an ale tastes like I advise you to get your hands on a freshly tapped ruby-coloured pint of naturally fermented and carbonated goodness.
~ Blanckey The Brewer