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**titorres44** · 10-22-2016, 12:40 AM

DO Measurement in your wert is fairly simple

I spent a significant amount of time looking for DO meters and probes for our brewery so I may have more to say than necessary.

The short answer: if you're NOT measuring final beer you're usually in the ppm range and can measure things in a glass, on a table, like the Hanna Edge meter. (attached “Improved Shelf life and Stability Manual” with DO tolerances at various stages and “Brewery Flyer” shows points of sampling in process) For wort, after the boil you're essentially at 0 ppm and need to get back to >10 ppm (recommended by wyeast) DO for the yeast. Without going all mathy the rate of solubility for O2 at near ambient temperatures is too slow to affect a measurement. If you were to let your sample sit for a few hours its DO at equilibrium at 70*F would be ~9 ppm so sample quickly if you want to be accurate. So a sample taken, without splashing, from a fermenter or kettle should be accurate to DO in solution without an effect of atmosphere. There are cheaper DO meters in the 0-25 ppm range but the effect of beer-compounds and measurement is not known. Generally, if a product is marketed towards the alcohol industry they have already compensated for alcohol and other relevant parameters to their device so it could be considered accurate.

The long answer: "The Beverly" by Hamilton ($7000), purchased through Gusmer enterprises is the most cost effective portable DO meter that is ready to go out of the box (attached “Beverly Data Sheet”). We needed it for packaging and were in the 0-50 ppb range (as liquid). Resolution of 1 ± 7 ppb, but you will save $4000 compared to the HACH Orbisphere (current market standard). I have done some calibrations to the orbisphere (at other breweries) and have gotten within 10 ppb of the orbisphere, which has resolution of 0.1 ± 1 ppb, so for what we need it was a good decision. Would be perfect for DO in wert.

Longer answer: you will see that there are thousands of dissolved oxygen sensors and meters but basically the market for brewers (low ppb range) is dominated by HACH followed by (in no particular order) Gusmer, Cole-Palmer, Mettler-Toledo, Thermo-Fisher and Emerson, maybe a few more. If I were asked to do any more DO measurements in the brewery I would buy a sensor and meter then build a sample chamber that accepts 1.5" TC fittings on a “TC tee” myself. To be in the 0-100 ppb range: optical probes are $2k-6k (average is $2.5k). In the ppm range: optical probes are $100-$500 (average is $200). Mettler-Toledo (attached “sales-Medler Measurement Options) has some $2000 sensors with meters that range from: your own ipad or laptop (essentially free) to $2000 non-portable meters to $5000 portable units. The reps. from Mettler are great and I would go with either them or Hamilton depending on what part of the process the brewers want to measure as each company has products that integrate better or worse with 1.5” TC or NPT threading.

Longer than necessary answer: Generally, DO measurement involves a sample chamber (or a coffee mug sitting on a table), sensor (usually probes) and a meter. The sensor interacts with the sample somehow, which produces a measurable signal to the meter, which converts the signal into something the user wants to know. Say you were to buy a DO probe and connect its output cable to a current meter (like a multi-meter). If you would sample a glass of beer you may get a reading, but likely the signal is too low to measure with a general meter. Additionally, if it were to measure, say 0.05mA, that would mean nothing without a calibration to some known standards. This is why it’s difficult to DIY these instruments. But, if you have someone experienced in this field (or know a local school with free interns) you can just buy a probe and use your own data acquisition method (commercial or DIY such as Arduino, Raspberry Pie or National Instruments) and derive your own conversion equation, as your meter. Another thing to consider if you plan on DIY is the effect of temperature and other compounds in solution (attached “ref-YSI The Dissolved Oxygen Handbook” more than anyone needs to know about the topic). HACH’s orbisphere has alcohol and temperature compensation built into their algorithm. If your probe is affected by alcohol you would need to incorporate this into your conversion from mA (or nA) to DO value. All probes (that I know of) are affected by temperature. There are main two types of sensors for the brewing world: electrochemical (EC) and Optical. EC sensors selectively allow diffusion of O2 into electrolyte chamber then, with voltage applied, electrodes convert O2 to OH. The current is measured and after a proprietary conversion factor within the meter (or one you derive yourself) it spits out a DO concentration. Downfall is they drift negatively over time, need to be replaced, affected by other chemical compounds in beer, require warm up and sometimes are flow dependent. The other is optical, which emit blue light, which is quenched (or “turned off”) in presence of oxygen, no flow required. Some sensors also emit red light to the surface of the probe which is used as a reference to compare the measurement to. The reduction of blue light is measured by a photodiode and after some proprietary conversion equation (or your own derived equation), spits out a concentration. Optical are generally considered the standard for beer, but are strongly temperature dependent and mildly alcohol, pH and salinity dependent. My suggestion, if you have read this far, is to stick with an established probe and meter combination that is marketed towards the brewing industry. That usually means someone way smarter has evaluated what parameters impact DO measurement for their device and has compensated their algorithm accordingly to a reproducible quantity. If you choose to go the DIY route and just buy a probe and derive your own equation for data acquisition, tell me how you did it!

Attachments were too large to upload on ProBrewer so heres a dropbox link: https://www.dropbox.com/sh/31ww6g8g4...8u9azkRIa?dl=0

Tim Torres
QA/Lab
Tractor Brewing Company
Albuquerque, NM

**TL Services** · 10-23-2016, 03:53 PM

Just a couple of things to add into the mix here:

- Using an open sample container for dissolved oxygen measurement means the sample can either absorb or lose O2 to the air, rendering the result inaccurate at best or meaningless at worst. This is why sensors are either installed inline or, in the case of portable meters, in a flow chamber. That way the result is representative of the liquid being analysed;

- The majority of electrochemical sensors are based on the Clarke Cell but with the addition of a third electrode (often referred to as the 'guard electrode') which eliminates the effect of other compounds. These tend to have an effect only at lower levels, so in the ppb range, which is why the DO2 meters for high level don't use this addition;

- All good sensors, whether optical or electrochemical, will incorporate a temperature measurement device (usually a thermistor or platinum resistance) so the meter to which they are attached can give a compensated reading without the need for manual correction.

The best advice I can give is to consider what your measurement applications will be: Wort, final product or throughout the process; this will help you to narrow down the most suitable instruments. Then talk to similar users and see what their 'real world' experiences are.

All meters and technologies have their plus and minus points; prices can vary widely and what suits one person won't necessarily suit another.

Hope that helps!
Tim Lawrence EngTech MInstMC
Director - Teal Laboratory Service Limited

**czschoche** · 10-24-2016, 12:30 PM

Thanks for the responses gentlemen.

To clarify, I'm only looking to test DO in wort at this point, so a meter in the PPM range is what I'm looking for.

Tim Lawrence, you have echoed my concerns about an open sampling process possibly giving me inaccurate results, but Tim Torres suggests that the rate of atmospheric O2 pickup/loss by the sample would be slow enough that I can still get accurate results. Has anyone tested DO in wort samples in both an open and closed process and compared the results?

Thanks,

Corey

**TL Services** · 10-24-2016, 03:20 PM

Hi Corey,

If you are measuring wort O2 levels then one of the simpler meters, such as the ones designed for use in rivers, etc. would suffice. These are designed for high levels close to saturation, so around 10ppm, which is (conveniently!) similar to the level for oxygenated wort.

Fortunately, too, this would see only relatively minimal inaccuracies with an open sample. As an alternative it should be possible to make a simple flow chamber for the sensor; a controlled flow of wort through the chamber would allow a steady and acceptably accurate measurement to be made.

**dick murton** · 10-28-2016, 11:14 AM

I'm not disputing the need for a DO2 meter to validate wort oxygenation, but if your financial resources are too limited for a good quality piece of kit, then I would look at measuring the air or oxygen flow and pressure, and the wort flow, then calculating how much air/ oxygen needs to be added, and more to the point, fully dissolved. If you can be certain that the oxygen from the air or oxygen supply is dissolving fully, then mass addition calculations are really accurate. I have installed a number of systems using mass flow control with meter validation / alarm handling.

A couple of other points you are probably already well aware of - oxygen from air will only achieve about 10 ppm DO2 in wort - varying slightly with temperature and gravity. Oxygen from a pure oxygen supply can achieve up to about 30 ppm. So if you are using pure oxygen in order to get above 10 ppm, and you should only be doing this if the yeast needs it, and you meter range only goes up to about 10 ppm, then it will not actually be any use to you.

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