Adventures in Sour Beer: Which souring method reigns supreme?

Hey everyone! I’m Sydney and I’m a microbiology co-op student from the University of Guelph. Like many of you, I have a love for craft beer (and for microbiology)! When I realized I had the opportunity to combine both my interest in craft beer and my interest in microbiology by working at Escarpment Labs, it seemed like the perfect fit! Since starting my co-op term back in May of 2021, I’ve had the chance to work on some very cool projects. Today I will tell you about how I learned to homebrew and how I eventually made sour beers for sensory analysis that everyone at Escarpment was able to try. I’ll cover the different methods that I used to sour each beer, how sour these beers really were, and which souring method was deemed the ultimate winner! 

This is me during patio season this past summer.

Background

            Before I started my co-op term at Escarpment I had never brewed before (although I had made cider and kombucha because I think fermentations are cool!). Shortly after I began my co-op term, we decided that my project should be a fermentation project where I would have the opportunity to learn more about brewing. It would also be a useful learning experience for everyone at Escarpment to taste the differences between different souring methods firsthand that are used in the beer industry. The experiment involved making four different beers. Each beer had a very neutral flavour profile so that the souring method could shine through. The goal was to distinguish the impact that the various souring methods had on each beer and ultimately determine which souring methods make the best sour beer! After the beers were brewed, I set up a blind sensory tasting for any Escarpment employee who wanted to participate. I asked each participant to taste each beer and rank them on a scale of 1-5, with 1 being not sour at all and 5 being extremely sour. Then, I calculated the estimated total acidity (TA) of each beer by titrating the finished beer with 0.1M NaOH (I never thought that I would ever titrate anything past first year chemistry). Finally, I compared the perceived sourness scores from the participants to the TA of each beer, and to the final pH of each beer and the total acidity of each beer to determine which souring method makes the best sour beer!


Base Recipe 

This is the base recipe that I used to make each of the beers. The only difference between each beer was the souring method.

Ingredients 

-       2.5 kg of Pilsen Malt

-       1.5 kg of OIO Wheat 

-       25 g of Hallertau Hops

-       Yeast of choice (differed depending on souring method)

-       Bacteria of choice (differed depending on souring method)

Method 

1)    Add 17.5L of warm water and 10 mL of lactic acid to the Brewzilla. Re-circulate the water with the pump and heat it to 71°C. 

2)    When it reaches 71°C, hit “pause” and set the temperature to 65°C. Mash in the grains until the temperature reads 65°C. 

3)    Check the pH of the mash (should be ~ pH 5.5). Let the mash sit for 1 hour at 65°C while re-circulating using the pump. 

4)    After 1 hour, increase the temperature to 75°C. Stir until it reaches this temperature (should take ~ 5-10 minutes). 

5)    Lift the grain bed out of the Brewzilla and sparge with 13 L of hot water (water must be acidified with 5 mL of lactic acid). 

6)    Turn the Brewzilla up to 104°C and let it boil for 1 hour. With 15 minutes left in the boil, add the hops. 

7)    Turn off the heating elements and start running cool water through the coil to cool the wort until it reaches room temperature (~ 25°C). Take an original gravity and original pH measurement. 

8)    Sanitize a clean keg and transfer the wort to the keg. Pitch a homebrew sized pouch of yeast into the keg. *Note: there are extra steps involved here for making a kettle sour.

9)    Move the keg to a temperature-controlled area and let it ferment at room temperature for ~ 1 week. Measure the specific gravity every three days until you don’t see a change in gravity anymore. 

10) Transfer the finished beer to a cold room and let cold-crash for 3-4 days. 

11) Carbonate the beer and enjoy! 


Beer Descriptions

Photo from our sensory tasting (Credit to Richard for taking this photo). 

Beer #1: Lactic Magic Sour

Beer #1 was made with the base recipe described above and using Lactic Magic as the yeast strain. Lactic Magic is a super cool wild stain of Lachancea thermotolerans that naturally produces lactic acid from the glucose in your wort (this is a sour beer enthusiast’s and microbiologist’s dream yeast)! By using this yeast, brewers don’t have to worry about contaminating their equipment with the bacteria that’s normally used to make kettle sours or worry about the extra time and boiling step that’s required when souring with bacteria. Lactic Magic is expected to produce a beer with soft acidity, citrus, and tropical fruit characteristics.

Lactic Magic Sour Stats

Starting gravity

1.040

Final Gravity 

1.014

Starting pH

5.42

Average Sourness Rating

2.23

Final pH (at the time of bottling)

3.87

Total acidity

3.798 g/L of lactic acid

 

Lactic Magic Sour Comments from sensory participants

“Didn’t have much sourness but was nice and clean flavour wise”

“It’s ok but kinda boring”

“Very clean and not very sour but a perfect hint of acidity” 


Beer #2: Cali Clean Ale

For Beer #2, we wanted to create a very clean non-sour ale that could be used in comparison with the other three sour beers. To make this clean ale, we used the base recipe described above and pitched Cali as the yeast. Cali is one of our more popular yeast strains that is very versatile and suitable for any style of beer. It produces a very neutral flavour profile, which is why we chose to use it here! 

Cali Clean Ale Stats

Starting gravity

1.042

Final Gravity 

1.007

Starting pH

5.61

Average Sourness Rating 

1.77

Final pH (at the time of bottling)

4.22

Total acidity

5.022 g/L of lactic acid

 

Cali Clean Ale Comments from sensory participants

“A bit corn forward”

“Not very sour, pretty clean. Some fruitiness from the yeast. Malty backbone. 

“It smells really nice but falls flat on the taste”


Beer #3: Lacto 2.0 Kettle Sour

With Beer # 3, we attempted to make a kettle sour using Lacto 2.0 to sour the wort and Cali as the yeast strain. Lacto 2.0 is a blend of Lactobacillus plantarum and Lactobacillus rhamnosus which is meant to enhance the fruity flavours in a finished beer and provide red fruit and guava aromas. We made this kettle sour using the same base recipe as described above, but with a few extra steps. First, we pitched Lacto 2.0 directly into the Brewzilla during step 7 of the base recipe, but we only let the Brewzilla cool to 38°C instead of 25°C. This temperature was chosen because it’s the optimal for bacterial growth. Then we began monitoring the pH of the wort until the pH dropped below 3.5 (after ~ 2 days). When the target pH was achieved, we boiled the wort at 100°C for an hour to kill any remaining bacteria and added our hops during the last 15 minutes of the boil. Next, we transferred the cooled (and sour) wort to a clean keg and pitched Cali. Then we followed the remaining steps the same as the base recipe. (Side note: This beer was my personal favourite!)

Lacto 2.0 Kettle Sour Stats

Starting gravity

1.039

Final Gravity 

?? (I was too excited about making this kettle sour that I forgot to record the FG )

Starting pH

3.39 (After souring with Lacto 2.0 for two days)

Average Sourness Rating

3.54

Final pH (at the time of bottling)

3.44

Total acidity

6.696 g/L of lactic acid

 

Lacto 2.0 Kettle Sour Comments from sensory participants

“I really love this one! Tart but not too sour, pineapple, peach, and sour cherry notes. Very complex”

“Yum, no aftertaste”

“A bit too much green apple/pear for me on this one. Tasting more like a cider.”


Beer #4: Lactic acid spiked Cali ale (A sneaky sour)

For our final beer, we decided to make a sneaky sour by simply adding in food-grade lactic acid to Beer #2 (the Cali Clean Ale). To do this, we tested varying volumes of lactic acid in 100 mL of Beer #2 and measured the pH to determine the optimal dosing rate. We eventually settled on 0.4 mL of lactic acid/100 mL of beer. We then scaled this up to a 500 mL bottle and added 2 mL of lactic acid to each bottle of Beer #2. This souring method was certainly not a winner! 

Lactic Acid Spiked Cali Ale Stats

Starting gravity

1.042

Final Gravity 

1.007

Starting pH

5.61

Average Sourness Rating

3.07

Final pH (at the time of bottling)

3.41

Total acidity

4.896 g/L of lactic acid

 
Lactic Acid Spiked Cali Ale Comments from sensory participants

“A bit less sour than Beer #3, allowing the funk to come through more.”

“Beer # 4 was the most bland.”


Final Verdict: Which Souring Method Makes the Best Sour Beer?

Figure 1. This boxplot is showing each individual participant’s rating of each sour beer on a scale from 1-5 with 1 being not sour and 5 being very sour. Total acidity (TA) and pH is also shown for each beer. (Thank you to Hana for helping me make this graph in R!!)

 

Figure 2: Bar graph showing the average sourness rating of each beer as ranked by the sensory participants. 

 

Final Thoughts

Each beer had its own unique characteristics which set each of them apart from one another. With a lot of help from Hana (another of Escarpment’s amazing co-op students), I was able to create the boxplot shown in Figure 1. This boxplot shows the sourness rating from the sensory participants on the y axis and beer sample on the x axis. Below each box you can also see the pH and the TA of each beer. The dots represent individual ratings from each participant’s response after tasting the beer (n=13). Figure 2 is a bar graph that shows the average sourness rating of each beer from the sensory tasting. As expected, the average sourness rating of each beer corresponds to the pH of each beer. The Lacto 2.0 Kettle Sour had the highest average sourness ranking of 3.54, and the second lowest pH of 3.44. The Lactic Acid Spiked Cali Ale had the second highest perceived sourness rating of 3.07 with the lowest pH at 3.41. Next was the Lactic Magic Sour with a perceived sourness rating of 2.23 and a pH of 3.87. Finally, the Cali Ale had the lowest perceived sourness with an average rating of 1.77 and the highest pH at 4.22. 

Technically speaking, pH is a measurement of the concentration of dissociated acids in a solution. Although this seems like it wouldn’t mean much to a brewer, the pH measurement of a sour beer correlates to the intensity of the acid that will be perceived by the beer drinker. So, it makes sense that the two beers with the lowest pH (Lacto 2.0 Kettle Sour and Lactic Acid Spiked Ale) were also the two beers that were perceived as being the sourest. However, something that I didn’t expect to see was that the TA had no correlation to the perceived sourness of the beers or to the pH of the beers. TA is a measurement of the total acid concentration in a solution. Because we know that lactic acid is being produced during these fermentations, then we can measure the amount of lactic acid in the final product. As expected, the Lacto 2.0 Kettle Sour had the most TA with 6.696 g/L of lactic acid. What was unexpected is that the Cali Clean Ale had the second highest TA with 5.022 g/L of lactic acid. This was very interesting because the Cali Clean Ale was clearly perceived as the least sour beer and wasn’t meant to be sour at all. Both the Lactic Magic Sour and the Lactic Acid Spiked Ale had less TA than the Cali Clean Ale despite these two beers being perceived as more sour. What I learned from this is that there can be acid present in a solution that doesn’t contribute to the perceived sourness of a beer. 

In the end, most of the sensory participants agreed that the Lacto 2.0 Kettle Sour was the ultimate sour beer! This beer was clearly ranked as the sourest, along with having the second-lowest pH, and the most TA. But something that perceived sourness, pH, and TA doesn’t tell you is the overall complexity of the beer. The Lacto 2.0 Kettle Sour was clearly the most complex of the four beers. It had some interesting fruity notes and the most complex sourness. The Lactic Magic Sour had a softer acidity and wasn’t very complex. Unfortunately, something that we learned after brewing this beer was that Lactic Magic requires dextrose to be added to produce more lactic acid. This had an impact on the final taste and sourness of this beer and is something that we might want to try in the future. The Lactic Acid Spiked Cali Ale also had no complexity. This shows how Lactobacillus spp. contribute other secondary metabolites to beer that can’t be achieved by simply adding lactic acid and explains the extra complexity that was found in the Lacto 2.0 Kettle Sour. This project ultimately showed us that TA and pH measurements are important quantitative measures for brewers to use when making sour beer, but tasting is the best test for brewing the best sour!

I had a really great time learning to brew and doing this whole project! I want to thank Evan and Adam for teaching me to brew and for providing all the expertise when it came to making the beer and Hana for all of her help with plotting out the data! 

 

References

Beer 8. Master the Method. (n.d.). Beer 8. Master the Method. Retrieved December 8, 2021, from https://www.asbcnet.org/Methods/BeerMethods/Pages/Beer-8-MasterMethod.aspx

Boulton, R. (1980). The Relationships between Total Acidity, Titratable Acidity and pH in Wine. American Journal of Enology and Viticulture, 31(1), 76–80. 

Understanding pH and Titratable Acidity in Sour Beer: Tools for Brewers and Enthusiasts Alike. (n.d.). Craft Beer & Brewing. Retrieved December 8, 2021, from https://beerandbrewing.com/understanding-ph-and-titratable-acidity-in-sour-beer-tools-for-brewers-and/

Plane, R. A., Mattick, L. R., & Weirs, L. D. (1980). An Acidity Index for the Taste of Wines. American Journal of Enology and Viticulture, 31(3), 265–268.