What's important to remember is that it's the release of the cytosolic compounds that is going to produce the off flavors. Autolysis takes months to occur at the homebrew scale, whereas cell death from killer toxins COULD occur much quicker.
The more reading I do, the more moving parts this whole CBC-1 "killer yeast" situation develops...
Q#1: Does CBC-1 possess the K-1 toxin, the K-28 toxin, or both?
Each of these toxins has a different MOA, and each has distinct activity and degradation properties and kinetics. Knowing the answer to this would help to understand how truly potent/significant it's "killer" moniker truly is in the setting of brewing a batch a beer. Though as you'll see from the info in my post, presence/absence of the K-28 toxin is probably of marginal significance to overall effects on brewing yeasts.
Q#2: How do the wort characteristics affect CBC-1's killer activity?
From these 2 articles:
http://www.microbiologyresearch.org...498&checksum=68706C3BF7107413A7094CDB64027DC0
http://www.microbiologyresearch.org...est&checksum=C2C0F23601CBC6354C60DE87B3ECB99E
There are pretty well-defined conditions that increase/decrease killing activity. Specifically:
--Log-phase cells were "most susceptible" to the effects of both killing factors (Note: I'm assuming KF1 & KF2 as described in these articles correlate w/ current nomenclature of K-1 and K-28. But this could be wrong...) as compared to "resting-phase cells". In fact, stationary-phase cells were actually described as "completely resistant" to the effects of KF1.
--During a 12h incubation experiment, KF1 was truly cidal via standard definitions (>= 99.9% killing of original viable inoculum) whereas KF2 was really only static (inhibited growth c/w a growth control).
--KF1 is thermolabile; total inactivation occurred in 90min @ 28*C (82*F); ~50% inactivation @ 25*C (77*F), and only slight degradation appeared to occur after 24h of incubation at 22*C (72*F).
--KF2 is much more thermostable (only 50% degradation over 4h at 60*C).
--The optimum pH range for the production, stability, and activity of KF1 is 4.6-4.8. "No active KF1 solutions were produced in complete medium above pH 5.0." Production of KF1 did appear to occur at pH 3.6-4.4, but it was lower and degraded quickly.
--The optimum pH for production of KF2 was 4.0-4.8 but considerable KF2 activity (60% of optimum activity) was observed at pH 5.8.
From the exbeeriment done on IPA pH, I noted that the pH's of those IPAs prior to packaging were shown as 4.4 & 4.5. (
http://brulosophy.com/2016/08/08/water-chemistry-pt-5-boil-ph-in-an-ipa-exbeeriment-results/)
What the heck does this all mean???
I guess my bottom-line assessment of all this toxin research is that when CBC-1 is used as a conditioning strain:
1--It probably doesn't produce a lot of toxin
2--The toxin that is produced is probably degraded fairly quickly
3--Most of the sensitive cells present are probably in the dormant/resting phase and are therefore probably fairly resistant to the effects of the toxin(s)
4--Not a lot of actual sensitive cell killing occurs
I'd hypothesize that when used as a conditioning/carbonating strain (with added simple sugars during this step), CBC-1 probably is awesome because:
1--Does an effective job of suppressing the re-activation of log-phase growth of previously-used yeast(s) in the primary fermentation when you add priming sugars
2--Doesn't cause a lot of cell lysis (minimizing concerns of imparting off-flavors)
3--Produces a clean, reproducible carbonation and doesn't mess with the mouthfeel as it does not use maltotriose (which should be present in significant quantities for ferments where S-04 and T-58 are used)
4--Helps to stabilize the flavor profile (potentially) by minimizing activation of the primary ferment strains after packaging
Other thoughts welcome...
