How long to sterilise with PBW?

[hoppyscotty]

Received a new refurbished keg today. Though it looks clean as a whistle visually I'm running some PBW through it and will rinse and run some starsan through too before putting any beer in. I want to put a batch of lager in there tonight so would half a day of soaking in cold PBW solution be enough to sterilise it enough? I'm impatient and want to free up my fermenter for the weekend. Think I should be OK on the basis it looked pretty clean to start with, but just thought I'd consult the hive.

Ta.

 

[ssashton]

10minutes should be enough contact time, certainly for StarSan, I do the same for PBW.

 

[Mayor of Simpleton]

PBW doesn't sanitise; it is for cleaning. I usually clean my kegs with a 20-30 minute PBW soak; rinse with water and then sanitise with Starsan. The Starsan only needs a short 1 minute or so contact time. This has always worked fine for me.

 

[ssashton]

That's not quite true, PBW is highly alkaline to the point that most microorganisms can not survive. It's a good pairing with Starsan because that works by being highly acidic.

If you have some litmus paper try sticking a bit in each of the cleaners - they send it off the scale at both ends!

P.S. I'd give starsan more than 1 minute. Even general surface sanitizer based on benzalkonium chloride recommends 2-3 minutes before wiping it off.

 

[ssashton]

I'm brewing today so thought I'd do the test also with wife's PH meter.

4 weeks old star-san (used once): PH 2.39

Fresh Starsan: PH 2.24

PBW (Sodium Percarbonate) 1 desert spoon / 5L: PH 9.56

PBW 2 desert spoon / 5L: PH 9.69

Very interesting to me that despite doubling the PBW the PH level does not go much higher. It seems PH 9.5 is about the limit of sodium percarbonate. So if you are using more than 1 desert spoon / 5L it's kind of a waste.

This website* has some very good info on PH control of microorganisms. Specifically this graph:

Most bacteria are neutrophiles and grow best at near-neutral pH (center curve). Acidophiles have optimal growth at pH values near 3 and alkaliphiles have optimal growth at pH values above 9.

Either StarSan or PBW will halt neutrophile microorganism growth which is the vast majority of bacteria and the one of interest because beer PH is in that range. The two extremes; acidophile and alkaliphile will be halted by PBW and StarSan respectively but are not really a major concern because once you fill a vessel with beer or wort you will be in a range of PH 6-7 and additionally the yeast pitch inoculates it.

* The Effects of pH on Microbial Growth | Microbiology

EDIT: Food scientist wifes note: Better to go acid than alkaline because the worse bacteria tend to be on the alkaliphile side.