Until the 19th century, the majority of beer brewed throughout the world was consumed locally because it had a short shelf life. Consequently, brewers set out to develop a product with excellent microbiological stability, and since then it has become common practice for breweries to filter and pasteurise their beer. These two processes remove yeast and any sediment, leaving a crystal clear and crisp looking product, as well as destroying any bacteria. Increasing the stability and the shelf life from days to months enabled the most popular brands to dominate the world market. Whilst there is an ongoing debate as to how filtering or pasteurising affects the beer, my opinion is that these processes can have a significant detrimental impact upon the characteristic flavours and taste of the beer. My opinion and appreciation towards beer has changed significantly since I moved to the Czech Republic, where I’ve had the opportunity to try many amazing beers from around the country.
The larger multinational breweries have us convinced that the perfect beer should be filtered and crystal clear; unfortunately these beers often have a generic taste with little flavour. There are various degrees of filtration which can be defined as rough, fine or sterile. One of the main aims of filtration is to remove dead yeast from the beer. Dead yeast cells breakdown in a process known as autolysis, which releases various compounds and enzymes which can influence the taste of the beer. If the beer is to be stored for longer periods of time, then sterile filtration is almost essential. However this will also remove proteins and macromolecules, which also contribute to flavour. Natural carbonation, which is a by-product of yeast fermentation, is also lost during the filtering process, therefore filtered beer has to be force carbonated prior to bottling or serving from a keg. Thankfully this has been somewhat addressed by the emergence of craft beer industry, which has returned to the more traditional efforts of brewing smaller batches of beer which spend less time in transit and storage as they are predominately sold in the local region. The established commercial breweries, at least those in the Czech Republic, have responded by introducing, or increasing production and distribution of unfiltered beer, which is labelled ‘nefiltrovaný pivo’. Pilsner Urquell do a fantastic unfiltered beer, and the one from Staropramen isn’t too bad either, although with more than 300 microbreweries throughout the country, there is plenty of choice should you wish to deviate from the mainstream brands and opt for something a little more unique.
Prior to transport from the larger commercial breweries, beer is heated to 60 ºC in a process known as pasteurisation; this destroys any yeast and prevents the growth of bacteria. Whilst this extends the shelf life of the beer, providing valuable time for transport and storage, it also alters the chemical composition of the beer, which has an adverse effect on flavour. In the Czech Republic this has been addressed by serving unpasteurized beer dispensed from large tanks, which is known as ‘tankové pivo’, or pivo z tanku.
The room in the pub or restaurant that houses the tanks is thermally insulated and kept at a constant temperature in the region of 7-10 °C. Beer is transferred from a truck into a sterile sealed polypropylene bag within the tank, each of which has a capacity of between five and ten hectolitres. To tap the beer, a compressor is used to push air into the space between the tank wall and the polypropylene bag, so the beer does not come into contact with air until it’s poured. As these processes ensure that the beer is protected from both oxidation and any drastic changes in temperature, this results in a smoother beer with less bubbles. It’s also fresh, perfectly preserved, and retains the original properties that the brewers intended.
The downside to this approach is that unpasteurised beer has a shorter shelf life and only remains fresh for around three weeks. This is only a viable option for pubs and restaurants that regularly sell high volumes of beer. However, tankové pivo has become an indicator of a decent pub that will look after the beer, and definitely something you want to try when you’re in Czech Republic.