[richardt]

Been reading the "Yeast" book.  They say yeast washing is done with phosphoric acid (at pH between 2.0 and 2.5) and at cold temps 36-40 F (2-4 C).

Other than warmer temps, how is this different from sanitizing my equipment with StarSan? 
Am I leaving viable wild yeasts behind in my fermenters and kegs if I just use StarSan?

[johnf]

Low pH is not Star-San's mechanism of action, it is simply a required condition.

So straight phosphoric acid at pH = 2.0 would be a horrible method of sanitizing brewing equipment, yes.

[richardt]

What is StarSan's mechanism of action, then?

StarSan has 50% Phosporic Acid, 15% Dodecylbenzenesulfonic Acid (a detergent), and 15% "inert ingredients."

I'm just curious how yeast washing with phosphoric acid at low temps can kill bacteria, but not yeast (or wild yeast); but StarSan with 50% Phosphoric Acid when used at ambient temperatures is an effective sanitizer (and presumably kills bacteria and all yeast strains).

[johnf]

What is StarSan's mechanism of action, then?

StarSan has 50% Phosporic Acid, 15% Dodecylbenzenesulfonic Acid (a detergent), and 15% "inert ingredients."

I'm just curious how yeast washing with phosphoric acid at low temps can kill bacteria, but not yeast (or wild yeast); but StarSan with 50% Phosphoric Acid when used at ambient temperatures is an effective sanitizer (and presumably kills bacteria and all yeast strains).

Star San is an acid anionic sanitizer. Here is a brief description of how they work:

http://books.google.com/books?id=lCRxcp3gfhUC&pg=PA180&lpg=PA180&dq=acid+anionic+sanitizer+mechanism&source=bl&ots=oOdpNfn5b8&sig=BFDwDZJtIT_H1mVtXMVvCMPED9k&hl=en&ei=uKrgTIX_OcGAlAfd0MWcAw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBMQ6AEwAA#v=onepage&q=acid%20anionic%20sanitizer%20mechanism&f=false

The salient point being that the surfactant is what is doing the sanitizing directly, the phosphoric acid is there to provide the proper pH environment.

[richardt]

Johnf,
Thanks for the link.  I found it quite informative.

It is an excerpt from "Principles of Food Sanitation," by Norman G. Marriott and Robert B. Gravani. 
Here's what they have to say about acid anionic sanitizers (truncated version):

"Acid anionic sanitizers act rapidly and kill a broad spectrum of bacteria and have good bacteriophage activity.  ...These sanitizers... ... have limited and varied antimicrobial activity (including poor yeast and mold activity)... [italics added] The antimicrobial effect of acid anionics appears to be through reaction of the surfactant, with positively charged bacteria by ionic attraction to penetrate cell walls and disrupt cellular function."

The rest of the chapter goes on to say:
There are bacteria that are resistant to acids or can develop acid resistance.
Peroxyacetic acid works on the oxidation principle and is effective against yeast.
Rotating sanitizers and methods helps prevent the development of sanitizer resistance.

It brings me back to my original concern about yeast washing and sanitizing equipment with acids (although my initial hypothesis may have been incorrect).
StarSan may not be eradicating the wild yeasts and molds in my brewing equipment. 
StarSan may be missing some acid-tolerant bacteria, too.

[johnf]

In general the acid tolerant bacteria won't grow in beer.

As for wild yeast, that might be more of a concern. I personally use iodophor and star-san at different points in the process and I sometimes hope this will save me from organisms resistant to one or the other. The real reason I use both though is more of a preference for the foaming sanitizer at certain points and for non-foaming at other points.

Acid anionic sanitizers are very popular in breweries which suggest that it may be the best solution. Halogen based sanitizers aren't perfect either.

[richardt]

In general the acid tolerant bacteria won't grow in beer...

Not trying to be snarky, but, there are a few important acid-tolerant bacteria that do grow in beer:  Microaerophillic (low oxygen), acid-tolerant organisms from genera like Lactobacillus, Pediococcus and Streptococcus.  Oxygen permitting, Acetobacter can also turn your beer into vinegar.  Some Belgian styles actually utilize these bacteria.

Hopefully, the detergent action within StarSan gets these bugs.  Yet, it still makes me wonder if the wild yeasts and molds are being adequately killed if I only use StarSan.  It may explain a subtle "house flavor" in the last few batches that some identify as mildly "phenolic."

[johnf]

lacto and acetobacter don't grow well in most finished beer (the presence of alcohol and lack of oxygen being limiting factors).

Obviously pedio grows well enough in finished beer.

[zorch]

Other than warmer temps, how is this different from sanitizing my equipment with StarSan? 
Am I leaving viable wild yeasts behind in my fermenters and kegs if I just use StarSan?

One huge difference is perhaps obvious, but when I am sanitizing my equipment it's already _clean_ - I've rinsed out all the chunks, soaked it in PBW, scrubbed it with soap and water, etc. 

To be fair, the ultimate answer to your second question is _yes_ - There are always going to be some small number of mold spores or wild yeast cells left over even after sanitizing, no matter what you are using.    Sanitizing != sterilizing.     So, you are correct that StarSan isn't going to totally eliminate all wild yeasts (and may in fact not do that great a job on these critters), but as long as you do a thorough job in cleaning, and of course pitch enough yeast, it shouldn't be an issue...  At least up to the point where it's no longer possible to clean your gear properly (scratched buckets, funky hoses, etc).

It may explain a subtle "house flavor" in the last few batches that some identify as mildly "phenolic."

If you are trying to get at the source of these mildly phenolic flavors, I would start first by asking:
- Am I able to control my fermentation temperatures adequately?
- Is my fermentation temperature in the correct range for the strain of yeast I'm using?
- Did I pitch enough yeast?

Not to say that you don't have a colony of bad bugs in your equipment.   But I would guess that it's more likely an issue with your fermentation.

[richardt]

Zorch,

I clean the equipment well each and every time.  Pretty OCD about that. 

What concerns me is that my go to sanitizer used for all steps may not be the all-encompassing sanitizer I thought it was.  I may have to use more than one sanitizer throught the entire process to eradicate the yeast/wild yeast in the buckets and tubing if StarSan alone isn't doing it.

"Yes" to your last 3 questions.  Temp controlled fridge, Temp kept between 64 and 68 F for Wyeast 1056, 2 Liter yeast starter pitched.

One definite possibility could be contamination as the yeast are now 4 th generation.  I don't have a lab so free-floating yeast are likely dropping in outside on the patio, in the kitchen, and/or the garage as I'm doing all the various steps in brewing, fermenting, and transferring, though I do take every step I can to sanitize surfaces (e.g., star san spray, isopropyl alcoholo 70% wipes, etc.) before transfers.

Probably just better to forget the Yeast farming / reuse and just buy new packs periodically.