High DO in Fermenter

[monkeybrewer]

equipment

it's the meter or the sampling...even after a filter run (that inherently adds some O2 to the beer), if you keep checking the DO in the brite, within an hour or so it will read 0 as the oxidation reactions have occurred. If you are getting O2 readings after ferment it must be the meter for the same reason.
Cheers

[Inthelab]

I just measured an old Amstel bottle that was purchased 6 months ago. It read 42ppb. You might be on to something.

Bingo! your meter needs calibration, and old Amstel should be sub 6ppb.

[TL Services]

Whatever the sales rep said, there is absolutely no such thing as 'no + or -', sure an error may be small, but it will still exist.

Indeed, the suggestion that the meter can only resolve down to 6-8 ppb before reading zero contradicts his statement - if there was truly no error, then it would read smoothly down to zero, not make a jump from the level quoted. Either:

a) There is a 6-8ppb error at low level, or
b) The signal noise at that level contributes 6-8ppb of uncertainty

Inthelab's advice to check an old beer is good - this should read absolute minimal DO2, so clearly there is something wrong if your meter read 42ppb. What is significant is that all the measurements you've made that 'should' be close to zero are all around 40ppb, which suggests it is far more likely to be a meter issue than anything else, as the meter is the primary common factor across all these measurements.

I would seriously question the accuracy levels you're being quoted, on the basis of the following:

Both Hach (Orbisphere) and Haffmans, who have been building meters for the brewing industry for years, quote similar accuracies to each other:

For low-level: 1ppb +/-2% of the measured value
For high level: <5% of measured value

And these are using the different meter configurations I referred to in an earlier post, not just a wide-range sensing head.

I'm not familiar with Hamilton's calibration regime, but again, both Hach and Haffmans have calibration methods that are similar to each other, either:

a) Zero-level only, ie. setting a zero-point on a known oxygen-free standard, or
b) Two-point calibration, using one standard that is oxygen-free and another that is at a known level of O2

The only way to be sure a meter is reading accurately is to check at least two points. Preferably these should be either side of the normal analytical range, so as to give confidence that any measurements are as accurate as possible.

[AT-JeffT]

I called our co2 supplier and they said their co2 is typically 3ppb. So I did the zero point calibration on the unit.

I tested the two fermenters and got 15ppb and 10ppb.

Looks like calibration was the issue!



Thanks everyone for all the help. I'll be referencing this thread when I have some time to better understand the differences in DO meter technology.

[TL Services]

Glad to hear you got sorted!

Interesting (and concerning) how far an optical meter can drift under normal use.

[Greenbushguy]

Still seems high

I called our co2 supplier and they said their co2 is typically 3ppb. So I did the zero point calibration on the unit.

I tested the two fermenters and got 15ppb and 10ppb.

Looks like calibration was the issue!



Thanks everyone for all the help. I'll be referencing this thread when I have some time to better understand the differences in DO meter technology.

We also have a Hamilton Beverly unit at our brewery and we love it! Are your 10 and 15 ppb readings post fermentation? If so, that still seems rather high. We routinely get 0 ppb readings off of our beer in the fermenter post cold crash.