Kettle Sour Brewing
About our Kettle Sour on Tap
Written by Brewer Bryan Bastow
Sour beers are some of the most complex, diverse, and mysterious styles in the brewing world. Making sours beers well is an art form that takes great skill, knowledge, and experience. Producing sour beers is one of my favorite aspects of being a brewer because it’s so wildly different from making non-sour beers and requires a well developed knowledge base along with original creativity and often some improvisation. That being said I’m happy to announce the arrival of our newest sour beer creation: The “Kettle Sour”. Our kettle sour was a truly enjoyable and intriguing brew to produce, as it involves several aspects that are unique compared to our usual sour offerings. This project is the first attempt at Perrin to make a kettle sour beer, as well as the first time using the different techniques involved with ‘hot-side’ souring. The beer is best described as an “Americanized” version of a lambic or Berliner Wiesse that is imprinted with our own unique twists. The kettle sour is a newly developed style that is gaining popularity, especially among craft brewers in the United States. Kettle sours are often presented as a cost effective way for brewers that are new to making sour beers to produce a consistently good tasting sour without the extensive procedures involved with traditional souring methods. As a beer style that is still being developed and defined, each brewery seems to have their own unique preferences and methods for producing a kettle sour. As a completely new style within the sour beer category, kettle sours are a step towards having several different classifications of sour beers rather than just a few. Our production manager, John Stewart, is a strong advocate for producing kettle sours as well as diversifying sour styles, which he believes could reach the same vast classifications found within a huge style category such as ales. Referring to the different techniques used for souring beers John states, “It’s really using an ingredient we know and utilizing it in new ways.” He goes on “We’re using the lactobacillus bacteria in different ways and experimenting with the possibilities of how to produce sour beers. When we have brewers experimenting with new procedures it opens the doors to new souring techniques and drives the evolution of new styles.” As more experimentation takes place within this area, the more likely it will lead to some cool new styles. The kettle sour style is very important because it represents the beginning and furthering of sour beer evolution that is currently taking place. As brewers, it is truly exciting to not only see beer style evolution happen but be a part of it and participate in developing these new possibilities from the start.
John was the mastermind behind this recipe and an effective, though lesser used sour brewing technique. Most traditional sour beer is produced though inoculation of lactic acid bacteria or wild yeast followed by aging in a barrel or other vessel ranging from 6 months to several years. What differs in our kettle sour process was the inoculation of lactobacillus took place not in the barrel but in the brewhouse (also known as the “hot-side” of the brewing process). This technique creates several production advantages; the primary factor being aging time is reduced from upwards of a year to just a couple days. The beer was also boiled in the kettle directly following the souring process to completely kill off the lactic acid producing bacteria. The result is microbiologically stable wort free of bacteria prior to fermentation that contains the great acidity flavor that we all love. ‘Hot-side’ souring procedure avoids presenting bacteria into the cellar or tanks, and in turn virtually eliminates the risk of bacterial cross contamination of other non-sour beers. Although lactobacillus makes great sour beers it can be detrimental if it is present in any non-sour beer. Proper cellar practices and extensive micro testing in the lab are conducted to avoid and ensure all our production beers are free of such microbes. As the lab guy responsible for testing and ensuring our brewery and all non-sour beers are free of bacteria such as lactobacillus, the kettle sour was a welcomed change in souring procedure. The process used for the Kettle Sour was able to reduce the nervous reaction I have any time a sour product enters our cellar. Quick turn times, micro stability and down right delicious acidic flavor makes this kettle souring technique stand apart from others.
The Process:
The kettle sour is a great example of simple use of ingredients paired with masterful use of technique and some new innovations to create a beer with complex flavor profile and character. The malt bill consists of just 2-row malt and malted wheat. The mash was spilt up into two parts another unique step to this brewing process. The brewing technique revolved around producing a small partial batch of highly sour wort then lowering that acidity by adding another portion of wort back to it. The process started by mashing in one third of the total grist, which is 10 barrels for our 30 barrel brewhouse. Following the mash and lauter procedures, a short 10 minute boil was conducted to kill off any microbes which would ensure the wort was free of any bacteria so the only thing that would be growing during the propagation step was the lacto we inoculated with. The wort was cooled then transferred into the mash mixer which would act as the souring vessel in this process. Once in the mash tun we had all requirements needed for lactobacillus to grow and multiply: sugars for food, nutrients, anaerobic environment, and ideal temperature.
At this point we inoculated the wort with the bacterium species Lactobacillus delbrueckii. The mixer was left on at a slow speed and CO2 was gently but continually added to the vessel. This would ensure the ideal conditions were provided for quick propagation and high production of lactic acid. The bacterium was left to do its thing and kick out the flavor over the next 48 hours. This two day period was the extent of the souring stage resulting in the sharp tart flavor we were aiming to produce. During this time and throughout the process both pH and total acidity were measured to confirm the lactobacillus was working properly and creating the acid profile we wanted to reach. Once the acidity reached a desired level and we were satisfied with the taste the newly soured wort was transferred to the kettle. Next the second part of the mash consisting of the majority of the total grist was mashed in and lautered in to the kettle. The mash temperature for this beer was very low (144oF) in order to produce highly fermentable sugars and leave the beer with little to no residual sugar. Once the full 30 bbl of wort was in the kettle it was boiled for 75 minutes. The boil process in brewing serves several purposes including isomerizing hop alpha acids, evaporating water which raises the gravity, lowers pH, caramelizes sugars, etc. The greatest importance of the boil process for this beer was the sterilization of the wort by killing off any microbes that might be in the beer, in particular the large amount of lactobacillus that had been growing and multiplying over the last two days. From this point on we had a beer that featured the sour/tart flavor and was also microbiologically stable and free of any bacteria. Once the beer was in a fermentation tank, our house yeast was used to ferment the beer as we closely monitored pH, gravity, and acidity levels though out the ‘clean’ fermentation. From start to finish this beer only took 19 days to sour/’age’, ferment, and package. This is an incredibly short time to produce a sour beer compared to others that may take years to reach the same acid level and tart characteristics.
The Result:
As I taste the end result of this new brewing project I’m totally satisfied with this beer, a mighty fine example of what a sour beer should be, mighty fine. I think most of the brew team would agree that sour beers are some of our favorite beers to make as they always present interesting challenges for us to explore and experiment with. This kettle sour has a very light body and very low residual sugar content with an original gravity of 9.8 oPlato and a low ABV content of 3.7%. It has a light golden almost straw color with a thin brightly colored and vanishing head, along with a high clarity and brightness. Consisting of very light malt character and very low bitterness and little to no hop flavor, the acidity is able to shine through as the focus that represents the overall taste of the beer. Our head brewer ‘Wild Bill’ VanEenenaam describes the beer as light, crisp, and refreshing, making it the perfect summer time brew. Our Kettle Sour has a flavor profile that is defined by a light body and strong acidity at the fore-front, the same as any classic traditional Berliner Wiesse. There is an up-front sharp lactic acid sourness that is the distinguishing character of the beer. The tart flavor adds depth, complexity, and interestingly presents some slightly fruity, bubblegum, grape, and tropical notes that accentuate the acidity.
Following the same serving practices as the Berliner Wiesse style, this beer will be served with an optional syrup addition when you come to get your pint in the taproom. With some help from the kitchen we’ve cooked up both raspberry syrup and the more traditional (and more difficult to find) woodruff syrup. The syrups are lightly added to this style to slightly lower or cut down the sourness which results in a balance of the beer’s acidity with some sweetness. I encourage you to try the beer in all 3 forms: straight up (like a G), with raspberry syrup (red), and finally with woodruff syrup (green). This will give you the full spectrum of the beer and the style we wanted to produce.
It’s always good when the brew team gets the opportunity to play around with different or new brewing techniques. Furthermore there is still much that can be learned from making kettle sour beers. There is still a very wide range of experimentation that can take place into how sour beers can be produced and how brewers can best utilize ingredients such as lacto bacteria. In my opinion as a brewer it is not only fun and interesting, but also somewhat of a responsibility to use the modern technology, equipment, and procedures at hand in order to produce very traditional styles and the ‘old school’ flavor profiles associated with different beer styles. Although kettle sours are often objected by some who believe the new methods involved are not true to the traditional sour styles, we hope the beer we’ve made will win you over. Remember in the end we should embrace experimenting with new techniques to make sour beers, and focus on the most important factor: How does the beer taste? We hope this kettle sour will satisfy all you sour beer lovers that enjoy mouth-puckering goodness, and also remain accessible to those of you who are new to sour beer and have not yet been converted to the awesomeness that is sour beer.