Diving Deep In To Philly Sour

Back in December I posted an in-depth analysis of an attempt to patent the Philly Sour yeast. Contrary to the claims of the patent, Philly sour is a strain of Lachancea thermotolerans and therefore is not patentable. Regardless, it is currently licenced and produced by Lallemand, and is sold in both probrewer and homebrewer sized volumes. But while the patent is bull shit (and likely deceitful), the yeast itself is worth some exploration. For those unfamiliar with this yeast, it is a species of yeast (Lachancea thermotolerans) which produces lactic acid alongside alcohol. This allows you to produce a beer with a kettle sour-like character, but without the difficulty of using bacteria, mixed fermentation, or other approaches.

There has also been a lot of discussion over using this yeast – especially on its ability to be re-pitched. Many people have noted that re-pitching this yeast often results in lacklustre acid production. Lallemand, perhaps not unsurprisingly, recommends you pitch new yeast each time.

This post is the summary of over three months of experiments, testing in-detail the fermentation profile, re-pitchability, and other aspects, of this yeast. This is a somewhat technical writeup, so please leave a comment if anything needs clarification.

Note: One of my readers has translated this article to Hebrew. You can find the translation here.


If you want the short version:

Use a hemocytometer to count the yeast before repitching. Always pitch 1 million yeast per mL of wort. Do not adjust the pitch rate to the worts starting gravity. This will ensure consisted acidification of your wort when reusing the yeast.

Oxygenate well.

Perform a mash to make a more fermentable wort, or add glucose, to increase acid production.

3 months of work…that’s what I got

A Quick Background on Philly Sour

Before getting into the fine details, I think its worth taking a second to briefly talk about exactly what this yeast is. Lachancea is a genus (group of species) of yeasts that are closely related to the Saccharomyces genus (where brewing yeasts are found), but which differ in a few key characteristics. The main one is that most species in the Lachancea genus produce lactic acid along with ethanol when they ferment. Meaning that they have the potential as single-organism sour beer producers.

There are, however, some limitations to their usefulness in the brewery. Many are from cold geographical areas, meaning that their temperature tolerances are below ale temperatures. The major exception to this is Lachancea thermotolerans – which as the name suggests is tolerant to heat, with most strains growing at temperatures up to 28C to 30C. Contrary to the claims of the patent, this is the species to which Philly Sour belongs.

General Features of My Tests

To keep my results as consistent as possible, all of the tests unless otherwise noted were performed using hop-free wort made from dry malt extract, at a gravity of 1.045. All fermentations were performed in 50 mL volumes. All wort was sterilized in the mini-fermenters, using an Instant Pot, high pressure setting for 15 minutes (and yes, this truly sterilized the wort). Unless otherwise noted, 1 million viable yeast were pitched per millilitre of wort (e.g. 50 million cells were pitched into each test). Yeast densities were confirmed by hemocytometer, using trypan blue to ensure only live yeast were counted.

Note that a hemocytometer is critical for yeast counts. Lachancea cells are smaller than brewers yeast cells, and grow to higher densities in wort. This means that yeast slurry or starter calculators will lead to over-pitching of the beer. As you’ll soon see, this is an issue with this yeast.

Philly sour is a slower fermenter, according to the manufacturer taking 10 days to reach final gravity. As such, all fermentations were done over 10 days.

General Fermentation Characteristics

Philly sour shows some interesting fermentation dynamics. Full acidification occurs within 5 days, while attenuation of the wort takes a full 8 to 10 days (Figure 1). I suspect this may be due to a shift in metabolism, with simple sugars consumed early to make acid. The yeast may then transition to a metabolic state which allows for complex sugars to be fermented into alcohol. But that is just a guess

Graph of pH and wort gravity over a 10 day fermentation
Figure 1: pH and wort attenuation during Philly Sour fermentation.

Philly Sour shows a strong dependency of the pH of the final beer on the yeast pitch rate (Figure 2). Even modest deviations from the “ideal” pitch rate of ~1 million cells per ml of wort leads to dramatic differences in the beer’s terminal pH. Oddly, terminal pH did not seem to depend on the starting gravity, with a pitch rate of 1 million/mL giving a consistent pH across a range of starting gravities (Figure 3).

Graph of the pH of the finished beer versus initial pitch rate.
Figure 2: pH of the finished beer versus initial pitch rate (in millions of cells/mL).
Graph of terminal beer pH versus starting gravity.
Figure 3: Terminal pH of beers with various starting gravities, pitched with 1 million cells mL, with no adjustment of the pitch rate made for gravity.

The last basic aspect of yeast behaviour I assessed was the dependency of this strain on oxygen, based on reports that it is more oxygen dependent than brewers yeast. I lack an oxygen system, so instead I tested different degrees of shaking the wort prior to pitching. This was compared to US-05 (American Ale/Chico). Consistent with other reports, high oxygenation was needed to get full acidification (Figure 4) and attenuation (not shown).

Effect of oxygenation on terminal pH
Figure 4: Effect of oxygenation on the terminal pH of beer fermented with Philly Sour versus US-05. None: not shaken, Low: shaken for 5 sec, Med: shaken for 30 sec, High: shaken for 1 min.

Repitching and Enhancing Acid Production

Aside from the basic work-up done above, I also probed some of the issues and tweaks that others have mentioned when using this yeast. The first thing I tackled was whether it can be re-pitched. Many brewers have reported that repitches do not generate the same amount of acid as the first use of the yeast. I suspected the decreased acid production was likely due to over-pitching (Figure 2), and this appears to be the issue. When re-pitched at 1 million viable cells per mL of wort, a consistent terminal pH was observed out to at least the 10th repitch (Figure 5). Given the lack of change in terminal pH or gravity in these batches, I suspect this yeast can be repitched indefinitely.

Terminal pH over multiple yeast repitches
Figure 5: Terminal pH is consistent for Philly Sour and US-05 when the pitch rate is held constant at 1 million/mL.

Given the low pH of the resulting beer, and the fact that this yeast has only recently been domesticated, I suspected that the yeast may not survive well once fermentation was complete. To test this possibility I performed trypan blue staining on sedimented yeast, starting 10 days after yeast pitch (Figure 6). Compared to a conventional ale strain, Philly Sour dies much more quickly (1%/day for Philly Sour versus ~0.1%/day for US-05). This may need to be taken into account if storing this yeast for future use, or when re-pitching older yeast.

Philly sour dies at about 1% of cells/day after fermentation is compelte.
Figure 6: Philly Sour dies quickly after fermentation is complete.

My final experiment was to test the effect of adding glucose to increase acid production. The manufacturer recommends either a low mash temperature, or the addition of glucose (also known as corn sugar or dextrose) up to 5g/100 mL (5% w/v) to improve acid production. I tested up to a 5% glucose addition (Figure 7), deliberately under-pitching the yeast at 0.25 million/mL in order to maximize any differences. As the manufacturer suggests, the addition of glucose enhances acid production.

Effect of added glucose on the final beer pH
Figure 7: Effect of added glucose on the terminal pH of the beer, 10 days post-pitch.

Conclusions & Future Experiments

Philly sour is an interesting yeast with several characteristics that make it of interest to those brewing quick sours. It also has several limitations that need to be taken into account when using or reusing this yeast. That said, a hemocytometer and basic microscope is all you need to be able to reuse this yeast indefinitely. I think we’ll see this yeast become a big part of many brewhouses.

And, with the cytometer comes the ability to fuck this yeasts patent application.

Look to my blog in the next week or two for a similar work-up of another new (and even cooler) brewing yeast. This will be followed by a head-to-head (-to-head?) comparison of Philly Sour with next weeks mystery yeast…and perhaps a 3rd mystery guest as well.

Until next time, keep on brewing (and seriously, fuck the Philly Sour patent)

33 thoughts on “Diving Deep In To Philly Sour

  • January 24, 2023 at 11:48 PM

    Fantastic article, thank you.
    Did you experiment with using dextrose alone to feed the yeast? To check how far the acid production goes.

    • January 25, 2023 at 7:19 AM

      No, I did not. I’m not a fan of Pilly’s flavour profile, so I didn’t go beyond what is in this post.

  • November 16, 2022 at 7:51 AM

    Just to verify, according to Lallemend stated Viability ≥ 1 x 109 CFU per gram of dry yeast, does that mean a single 11gram packet only contains 11billion cfu? Therefore, in a 12.5P 5 gallon batch, a single packet would only give 0.05M cells / mL / °P. Requiring 2 packets?

    • November 16, 2022 at 8:22 AM

      You’d have to ask Lallemand, I’m not sure what is in their dried packets. In my case, I was counting cells from a starter on my microscope.

  • March 8, 2022 at 2:43 PM

    I am confused about the numbers. Lallemand says 1g/L gives 5 bi cells/L and recommend it as optimal concentration for lactic acid production. It is more than you have tested, or am I missing something?

    • March 8, 2022 at 2:46 PM

      I used the numbers provided in their insert when I purchased the yeast. They may have changed the formulation since then.

      • March 8, 2022 at 3:16 PM

        Thanks. I downloaded the most recent datasheet and you are right. Sorry for the noise.

  • November 25, 2021 at 1:43 PM

    Awesome write up and information, lots of help for my current brew. Thanks!

  • August 7, 2021 at 7:54 AM


    i can afford of buying all of that gear for making homebrews, But i really want try to re-pitch this. Can you give me a hint: Around how many ml will 25l brew need? doesnt need to be accurate, but when ill try re-pitching i have somekind a reference 🙂
    Tablespoon less or more?

    • August 9, 2021 at 7:10 AM

      Without a way to count the yeast directly it is difficult, but as a general guideline:
      -Slurry from a previous batch will likely have ~1.5 billion cells per ml
      -A freshly prepared starter will have ~50 million/ml

      • September 27, 2022 at 12:42 PM

        Hi, very interesting post! Thanks for such great info

        I have a question. I have not a microscope, so I want to estimate how many ml to use for re-pitching from a yeast cake.
        Considering a desired pitch of 1million cells/ml, for a 20L batch I would need 20billions cells. Assuming that a slurry has 1.5billions cells/ml, according to my calculations, for a 20L batch I would have to use only 13ml of slurry… Is it correct? Am I missing something?

        • September 29, 2022 at 7:59 AM

          Your calculation is off, as you have to account for both volume and starting gravity. You want 1 million cells, per ml of beer, ***per degree plato*** (one degree plato is a specific gravity of ~1.004, so 4 degrees plato is ~1.016).

          So for a 20L batch at 1.050 OG (12.5 plato) you would need:
          -12.5 plato * 1 million/mL * 20,000 mL = 250,000,000,000 yeast (250 billion), or ~170 mL of slurry that is at 1.5 billion/mL.

          For a 20L at 1.080 OG (19 plato) you would need:
          -19 plato * 1 million/mL * 20,000 mL = 380 billion, or 250 mL (1 cup) of slurry.

          • September 29, 2022 at 10:19 AM

            I completely forgot the starting gravity… Thanks a lot!

  • July 7, 2021 at 5:06 PM

    Great write up! Have you tried pitching dry yeast vs rehydrated, and noticeable pros/cons?

    Also have you tried pre acidifying your wort to say 4.2-4.4 with lactic acid the pitching the yeast,
    i have read that this helps with a lower final Ph.


  • June 16, 2021 at 5:26 PM

    Very interesting stuff. Just using my first Philly Sour ( in fact any sour ), noticed day 2 pH 3.76 and then day 3 seemed to be 3.84. Since that time the gravity has started to drop more rapidly. Gravity fell 1.057 to 1.051 day 2, 1.051 to 1.049 day 3 and then 1.049 to 1.045 in the next 12 hours.
    Does this suggest lactic acid production is finishing and moving onto the ethanol phase?
    I’m fermenting at a rock steady 26 celsius, pitched one packet into 28 litres, unsure how to assess the cells per ml, I’m thinking an underpitch so not likely to get that low a pH but I’m aiming for 3.6 and then was going to add some kveik and bump the temp up.
    I’m in NZ and the PS is about 12 US dollars or 10 euros a packet here. So might try and save some from the next packet. I enjoyed the podcast as well.

    • June 17, 2021 at 11:51 AM

      The pH drop normally occurs first, followed by a gravity drop, so what you’re seeing is typical. Adding a kveik may push the pH a bit lower as some kveik produce a fair bit of acid, but so far my experience is that the pH you get with philly is pretty much the terminal pH. Whether this is a 2-phase fermentation (lactic acid transitioning to ethanol) or simultaneous lactic-acid + ethanol fermentation is unclear, as not enough is known of this organism to say. It is worth repitching, but you need some what to do a cell count, otherwise it is very easy to pitch at a rate which leads to under-acidificaion.

      • June 17, 2021 at 6:48 PM

        Thank you Brian
        Recalibrated pH meter today and retested, pH now 3.6 with both meters.
        Have also found out that I can get the philly sour for 5 us dollars so not as bad as I thought.
        Will see how it changes with the Kveik. Thanks for that advice as well.

  • May 11, 2021 at 11:44 AM

    This is an excellent write-up, thank you for taking the time to do this! Sorry if I missed it, but did you find an optimal fermentation temperature? If not, is there one that you prefer to use with this yeast?

    • May 11, 2021 at 1:10 PM

      I didn’t do anything with temperature and simply used the manufacturer’s recommended temperature (20C)

      • May 11, 2021 at 1:41 PM

        Thanks, I’ll give 20C a try first then. I noticed that they mention 20C is what they use for their “standard conditions wort”, but it’s also at the bottom of the recommended range so I wasn’t sure if it was considered the optimal temp.

  • March 24, 2021 at 5:38 PM

    Hi! Thank you for this fantastic post. Any idea on what the growth/multiplication rate of this yeast is? It would be useful to have a nice (even though unprecise) rule of thumb when repitching.

    • March 30, 2021 at 7:05 AM

      Not off hand, but the pitch rate (1 million/ml) is the critical value – too much above or below that and you may get sub-optimal souring.

  • February 24, 2021 at 4:51 PM

    Have you looked at the AEB strain at all?

    • February 25, 2021 at 8:01 AM

      No, as I do not have that strain as yet.

  • February 13, 2021 at 8:05 PM

    Thanks for the great work! Have you tried to dry it? I dried and successfully reused the Levulia alcomeno (I think it was called) L. thermotolerans sold by a wine yeast producer, I guess it would work for this one too?


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