Hey everyone,
For years we have been using Pentair o-dgms to check both liquid DO and oxygen levels when purging tanks. My question is specifically regarding the unit of measurement for gaseous O2 when checking purges. With the o-dgm you can select liquid or gas as the media so when taking beer readings we set the media to liquid and the unit to PPB and when checking purges or headspace we set the media to gas and the unit to %. We usually purge vessels low and slow overnight and aim for 0.05% O2 out the sidearm, which will drop a bit once we've pressurized up to 1 bar (0.02% or so). With this spec we see minimal O2 pickup in BBT (5-10ppb) and I am satisfied this is an acceptable level for us. Before you ask, yes we validate our O2 meters periodically with calibration grade CO2 and we also have recently started sending them off for 2 point calibration periodically as they tend to drift up with use.
My confusion arises because we recently had an issue with our keg rental supplier (who supplies cleaned, purged, and pressurized kegs to us) who informed me that their O2 spec for pressurized kegs is 50ppb. The kegs I checked from the problematic delivery ranged from 0.01% to 5% O2 and resulted in some very high liquid DOs in filled kegs and rapidly apparent quality issues obviously.
My question is this: 0.05% = 500,000ppb which seems like an absurdly high O2 number, but I know is acceptable for our processes. Scouring the MBAA forums I've seen keg purge targets being as low as 50-100ppb, and some insisting on close to 0 ppb. What gives? Am I missing something, or is our purge spec orders of magnitude higher that other people's in the industry?
Thanks in advance for any help!
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Francesco Mayell
Lead Brewer
Brixton Brewery
London
francesco.mayell@brixtonbrewery.com------------------------------