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.


TL:DR

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)

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