DO Readings Within Fermenters

[sdfellis]

Hi Everyone,

I'm new to this site, but I thought I would see if anyone could help shed some light with some issues we have been having. We just recently purchased a Hach Orbisphere 3100 so that we could measure DO levels and we were initially obtaining higher readings than we would have liked to have seen within our packaged beer. We traced back to the bright tanks and then to the fermenters so that we could see what kind of oxygen pick-up we were getting in the transfer process. Much to our surprise, we were obtaining DO levels of 20-50 ppb in our fermenters and we were surprised as we figured it should be at or near zero. I compared our new meter to another recently-calibrated meter a sales rep brought into the brewery for us and calibration of our unit did not appear to be the issue as the other meter gave the same readings. When dumping our cones we flush CO2 back into the tank through the CIP arm to ensure that oxygen isn't introduced during this process. Does anyone have any idea why we might be obtaining these high O2 readings within the fermenting tanks? Any help is appreciated. Thank you.

[dick murton]

If you are late dry hopping for aroma, then particularly if you are using whole hops, and don't nitrogen / CO2 purge thoroughly before addition, you risk creating a diacetyl bomb due to all the air (oxygen) you add with the hops - see other discussions re late hopping for additional comments on this. IF, and I accept it is a big if, your sprayhead is below the beer level, you may be introducing air / oxygen that way. Personally, I would not bother putting additional CO2 on top of the FV as, unless hugely overfilled, there will be a layer of CO2 produced from fermentation which will protect it. Do you have a sightglass attached to the CIP arm for cleaning purposes, which then allows gas (with even a small amount of air) to be blown into the bottom of the FV?

Is your CO2 pure enough?

If your yeast is thick and you allow air to go back into the FV via the yeast takeoff point, then this could cause the problem - again I think this unlikely, but....

[TL Services]

In addition to DM's excellent advice from a brewing perspective, I would suggest checking your sampling points, connections, etc. are all thoroughly tight and leak-free. Bearing in mind that air is 29% oxygen, it doesn't take much air ingress to create a ppb DO2 reading.

The same goes for transfer hoses, etc. where it is possibly for a worn seal or similar to allow in O2 even though there are no signs of liquid weep.

DO2 sampling in fermenter isn't the easiest as any solid material can cause flow issues; out of interest what sort of levels were you seeing between fermenter and package? There are some common causes of DO2 pick-up that can be quick wins once sorted!

NB. If you prefer not to quote process figures then please feel free to PM.

Best regards,
Tim Lawrence
Director - Teal Laboratory Service Limited

[TGTimm]

Anything on the suction side of a pump--including the pump seal--can introduce air into a transfer line--even the tiniest leak. I'd suggest a sight glass at the output side of your transfer pump(s) and monitor it carefully for tiny bubbles. Inspect everything on the suction side of your pump(s). Banded hose fittings are always suspect.

[PNWBG]

DO cure

I would not worry about the DO in the fermenter that much. Yeast needs oxygen to finish a healthy ferment. Once ferment is done though, be meticulous. If you monitor the ferment daily you know what day it will be done based on some graphing you can do. But, once you decide it's finished fermenting, plan to transer it quick and proper. Once ferment is done, be meticulous. Purge your transfer lines/hoses with co2. Also purge the bright tanks, but from the bottom ports. You can even sparge with co2 from the beginning of the transfer to the end. If you decide co2 from the top is best, remember, turning the psi of the co2 regulator higher isn't a better answer. These gasses are invisible and the higher the pressure of the gas going in, the more turbulence you cause and just mix more O2 in again. Get yourself a flow meter attached to your co2 line and let the gas flow in at 10-15cfm. Calculate your tank volume in cubic feet and you can see how many minutes to set your timer for when Purging the tanks with co2. Also, leave top tank lids slightly cracked to breathe out, not open fully.

The next thing to consider is the pump you use for transfers. Flexible impeller pumps cause the most oxygen to be introduced. Centrifugal is better and fast for transfers. Most ideal and time consuming way is with a peristatic pump. It's a lot softer during the transfer and causes less agitation when it reaches the tank cause it is pumping much slower and more controlled. This is really only ideal when barrel aging. While still talking about pumps, most Centrifugals have an air inlet valve because they are not self priming. Purge your lines there with co2 before the transfer and "if" you disconnect from it, make sure the valve is shut. It's pretty easy to leave it open and not know it while it is just sucking in air the entire time.

I think last it would be good to touch on DO numbers. If you're aiming for 0, good luck. You will waste too much money on gas. A target of 0.005-0.010ppm gain after fermenter is going to happen. Just get that DO lowered before force carbonating. Before bottling, make sure the DO is low for the next transfer to bottle.

Last thing I just thought of. Make sure your sanitizer is being mixed right. More doesn't make it better. The ozones or one step Sano chemicals are no rinse, which is great, but because they break down into unstable hydrogen peroxide and then that breaks down into h2O and O2, excess sanitizer in the solution will leave a residue, potentially increasing DO.

Well, that's enough texting for me. Do with this what you will. Cheers!