Lesson 2 - Warm and Cold Maturation
This lesson explores the processes of warm maturation and cold maturation. Warm maturation can also be described as flavour maturation This process removes negative or unwanted flavours from the beer post-fermentation. Cold maturation occurs at lower temperatures (below 0°C), which in turn causes haze-forming components to form. These components can then be removed by precipitation or clarification via centrifuge or filtration. This lesson highlights the importance of these processes, how they affect the quality of the final product, and how we manage these maturation steps.
Point of Reflection – Reconvene
Welcome back! So, what were your thoughts?
First of all, you would need to understand the trends in process time and the levels of flavour components within your beer brands.- Are your process times consistent by brand? How frequently do you exceed residence time on maturation vessels, and why?
- Do you see volatility in levels of diacetyl or off-flavours? Do you know why this variability occurs?
- A consistently warm maturation period at a set temperature
- A consistent reduction in VDKs to an acceptable level
- No negative flavours because beer transfer processes and the residence time in the maturation vessel are under control
- When beer is transferred out of warm maturation, it is true to type and has excellent flavour stability
- Standard operating procedures must be followed by all operators
- Vessels and pipework must be clean and sterile
- The beer transfer system from fermenter to maturation vessel must be deaerated and the receiving vessel must be blanketed with an inert gas, such as CO2 or N2, to minimise oxygen pick-up.
- Ensure that you adhere to target residence time in the maturation vessel
Traditional lagering
It is possible to achieve the objectives of maturation without keeping the beer warm at the end of fermentation. The term lagering in the traditional sense involves only cold maturation with a secondary fermentation. In traditional lagering CO2 levels can be increased using krausening. This involves adding 5-20% by volume of actively fermenting wort which stimulates a secondary fermentation. Some brewers use wort at low krausen while others at high krausen. Traditional lagering is done at temperatures dropping slowly from around 5°C to 0°C. Lagering is a longer process than warm maturation because the yeast is less active. With some strains of ale yeast, the temperature is too cold for the yeast to do anything so lager strains are almost always used. There used to be a rule in Germany that you lagered the beer for one week per °P. However, this is only done by the most traditional breweries today.
Lagering is often combined with spunding, where the maturation vessel pressure is controlled to allow the secondary fermentation to carbonate the beer to a specific level. Proponents of spunding feel that the mouthfeel from this type of carbonation is more pleasant than when CO2 is added later in the process. The theory is that the CO2 associates with nitrogenous material in the beer, changing the nature of the bubbles when they form later. Spunding also helps retain SO2 which is believed to improve flavour stability. Yeast cell count is also controlled to ensure lagering is consistent.
Generally, breweries use a batch process for all types of maturation. Beer is brewed and transferred as a batch between each stage of the process. However, it is possible to use continuous maturation.