22 · BBII 1/2008

Oxygen is of interest to the brewer for at least three

reasons. Firstly, the character of beer (clarity, colour, odour andtaste) is partly determined by the quantity of oxygen available to the yeast during fermentation.Secondly, the beer produced issubject to oxidation and thereforeshould be protected from theatmosphere throughout processingand in the package. Thirdly,aluminum can manufacturersspecify upper limits on theconcentration of air in cannedbeverages due to a risk ofcorrosive attack from oxygen.

Expert tasting panels can easilyrecognise beers which have beenoxidised. Noticeable changes take place within two hours afterpackaging when dissolved oxygenis too high. Physically the changesare accompanied by a decrease in colour type (the beer becomesreddish) and chemically by a decrease in sulphur dioxide, an increase in diacetyl, and anincrease in acetaldehyde. These

are sufficient reasons to make the control of dissolved oxygenlevels of prime importance in the brewery.

The most detectable off-flavour that arises from oxidation is a “cardboard” or “wet paper”taste produced by the reaction of polyphenols. Careful beerhandling in the brewery can result in packaged dissolved oxygenvalues of less than 100 ppb. At this level the shelf life will be greatly extended.

It is critical to accurately controloxygen levels at various steps in the production process sinceimproper amounts of that mightbe present will greatly affect thetaste of the final product.Furthermore, oxidation is anadditive process so all steps fromfermentation to the final packagemust be taken into account tomaximise the beer’s shelf life andtaste. Table 1 shows the expectedoxygen levels throughout thebrewing process.

It is not enough to simply knowthat oxygen measurements areimportant. It is critical to ensurethat correct measurements are made using in-line, portable or laboratory based analysers. In addition, a clear understandingof the benefits of electrochemicaloxygen sensor technology

IMPROVED SHELF LIFE AND QUALITY

O2-Measurements for the brewing industry

We know that improper amounts of oxygen present in various stages of the brewing process will greatly affect the final taste. Accurate oxygen analysis allows the brewer to control the

process so that the shelf life of beer can greatly be extended. A brief review of where to measureoxygen is provided in this article, followed by some helpful information on how to best make

oxygen measurements in-line, in-package and whilst using portable analysers. Finally, some technicaldetails are provided explaining the benefits of using electrochemical sensors for oxygen measurements.

Understanding of the importance of oxygen measurements at each step of the brewing process and how to best apply various solutions for making measurements will lead to improved

oxygen measurements in the brewery.

Chris Klein

Beverage Market Manager, started withHach Ultra in 1998 as a Regional SalesManager in the USA. In 2000 he waspromoted to Key Account Manager for SoftDrinks and Bottled Water in the Americas.Since 2005 he has been the BeverageMarket Manager and currently works at Hach Ultra’s global headquarters in Geneva, Switzerland. Contact: cklein@hachultra.com

Frank A. Dunand

Dunand has been the author of 15technical papers in the analytical chemistryfield before joining ORBISPHERE in 2002.He currently holds a position as SeniorProduct Manager at Hach Ultra heading a team managing all ORBISPHERE and POLYMETRON products. Contact: fdunand@hachultra.com

Picture 1: Orbisphere 3650 Portable Oxygen Analyser.

BBII 1/2008 · 23

(the most common analyticalmethod applied) is required inorder to make improved oxygenmeasurements in the brewery.

Where to measure oxygenAeration of wort

In traditional brewing operations,wort is saturated to a desireddissolved oxygen level of about 6-9 ppm, although some modernstrains of yeast can require up toabout 14 ppm. Oxygen is essentialfor adequate propagation of yeastcells during fermentation.

In the fermenter

The amount of dissolved oxygenin the fermenter is a usefulindication of the progress of fermentation. One day afterfermentation, oxygen levels fall toless than 30 parts per billion (ppb)and yeast breaks down the sugarsin solution, producing alcohol and other by-products. Some ofthese by-products are extremelysusceptible to oxidation andtherefore one objective for thebrewer is to ensure that oxygen

does not contact the beer in its journey from the fermenter to the final package.

CO2 recovery from the fermenter

Carbon dioxide, produced in largevolume during fermentation, canrepresent an important by-productfor brewers and many collect andpurify the gas for their own use,and even for sale. During CO2recovery from the fermenter it is necessary to ensure all the air is vented off using an oxygenanalyser.

Deaerated water

When the high gravity method of brewing is used, there is a need to ensure that deaeratedwater added in the final dilution of the beer has an adequately low level of dissolved oxygen.

Bright beer

A major source of air conta-mination in bright beer occurswhen it is transferred betweenvessels. After every tank transfer,or operation such as filtration, thebeer should be checked to ensure

Brewing process Oxygen level

In wort 6 - 14+ ppm

Fermentation < 30 ppb

Filtration 1 - 200 ppb

Bright beer after filtration 1 - 200 ppb

Beer at the filler 1 - 200 ppb

Package dissolved oxygen (bottle) 30 - 250 ppb

Package dissolved oxygen (can) 20 - 120 ppb

Total package oxygen 50 - 450 ppb

Table 1: Expected oxygen levels throughout the brewing process

24 · BBII 1/2008

it is not picking up dissolvedoxygen. Another source of aircontamination is inadequatelypurged vessels. Leaking pumpglands, leaking valves, and filteraid dosing pumps can also allowoxygen ingress. By measuringthroughout the process it ispossible to identify the source of any oxygen contamination.

In the package

If beer containing unsatisfactorylevels of oxygen is packaged,irreversible damage will be doneto the flavour profile. Any beer thatis filtered before packaging mustbe protected from oxygen since it no longer contains oxygen-consuming yeast.

In many breweries, responsibilityfor the quality of the beer changeshands at the filling machine, fromthe brewing department to thepackaging department. An in-linedissolved oxygen measurement at this point provides documentaryevidence of the quality of theproduct at the moment of thehandover. The packaging depart-ment, equally, must performspot checks on the performanceof the filling machine as well as quality control checks in the final package.

How to measure oxygenThe products offered to thebrewing industry by Hach Ultrabenefit from nearly half a centuryof expertise gained with leadingbrands, such as ORBISPHERE.The Hach Ultra ORBISPHEREoxygen sensor meets qualitymanagement rules and proceduresand its calibration is independentof the sample. Furthermore, Hach Ultra oxygen analysers can be used in-line, at-line and in the laboratory to measure bothprocess and final package oxygen.

Portable analysis

To identify the source of oxygencontamination, the Hach UltraORBISPHERE 3650 portableoxygen analyser (picture 1) can be used for spot checks but also has the facility to be lefton the sample point for severalhours in its “logging” mode.

When making measurements inwort or bright beer, it is imperativethat all gases are in solutionbefore oxygen is measured by the analyser. Any degassingthat might occur would artificiallyreduce the dissolved concen-tration value. When sampling beer,always fully open the pipeline

sample tap and regulate the beerflow using the flow control valveon the outlet side of the flowchamber.

In-line analysis

Sensor installation can be madeinto most parts of the beer line,including near bends and valves,but must be sited as far aspossible away from pumps(particularly just downstream ofthem). Sensors should be installedinto horizontal or rising mains,never falling mains. The sensorshould always lie horizontally.It is particularly important never to install an oxygen sensorvertically into the top of a pipelinesince an air pocket could betrapped there and effective CIPwould be impossible. All HachUltra ORBISPHERE systems aredesigned to withstand hot (100°C)or chemical cleaning-in-placewithout damage or performanceloss. It is also possible to measure multiple locations ormultiple gases (O2, CO2 or N2)with the same instrument using a Hach Ultra ORBISPHERE 510multichannel analyser (picture 2).For in-line analysis, the Hach UltraORBISPHERE 32003 ProAccinsertion/extraction valve allowsfor sensor removal and installationwithout having to drain the fluid in the line.

Picture 2: Orbisphere 510 Multi-channel Analyser.

Picture 3: Orbisphere 3650 PortableAnalyser with 29972 Package Piercer.

BBII 1/2008 · 25

In-package analysis

Samples are obtained from bottlesor cans with the Hach UltraORBISPHERE 29972 packagepiercer (picture 3) by applying a forcing gas of CO2 or N2 to drivethe beer out of the package andpast the oxygen sensor. Dissolvedoxygen can be measured usingthe Hach Ultra ORBISPHERE 3650Portable Analyser. Total packageoxygen (TPO) can either becalculated using a Hach UltraORBISPHERE 510 LaboratoryAnalyser (picture 3) or determinedautomatically by using the HachUltra ORBISPHERE 3625 totalpackage analyser (picture 4) by measuring the total liquid and headspace O2, whilst alsomeasuring CO2, and N2 from a single package.

Some important points should beobserved for accurate in-packagemeasurements:

1. Always measure packagesimmediately after filling andbefore pasteurisation becausethe heating process allowsdissolved oxygen to reactrapidly with the beer

2. Always shake packagesvigorously before piercingbecause this allows formationof smaller bubbles for rapidequilibration

3. The applied CO2 or N2 forcinggas pressure must be higherthan the pressure of the totaldissolved gases in the beer to prevent bubble formation

Benefits of electrochemicaloxygen sensorsBy far the most widespread in-linedissolved oxygen sensors belongto the category of membraneisolated electrochemical sensors,in which an electrical current isgenerated in direct proportion tothe partial pressure of the oxygenin the sample. The proportionalityconstant can be determined by a suitable calibration procedureusing the air as a source of knownoxygen partial pressure. Henry’slaw provides the link betweenpartial pressure and dissolvedconcentration in the sample.

Hach Ultra ORBISPHERE oxygensensors (picture 5) are of this type.Three unique design featuresmake the sensor suitable for highprecision oxygen measurementsunder harsh industrial conditions:

BLAUDIECK®

beverage hoses are absolutely neutral to tasteand odour and well-knownworldwide for their outstanding quality at reasonable price. They arethe right product for the safe and hygienic transport of a great varietyof products. With UPE liner they areresistant to extreme detergents anddisinfectants. Every hose type comply with all international recom-mendations, such as BfR and FDA.

Fluid TechnologyContiTech Specialists in rubber and plastics technology

BLAUDIECK®

Beverage Hoses:The attractive Alternative!

ContiTech Schlauch GmbHP.O.Box 1120, 34481 Korbach (Germany)industrial.hoses@fluid.contitech.de

Advantages ...q lining and cover resistant to oily and

fatty products and caustic solutionsq resistant to temperatures from -35 °C up to +95 °Cq resistant to steam up to +130 °C (for disinfection)q resistant to alcohol up to 45%

(with UPE liner up to 98%)q high quality fitting system for a hygienically

clean connection without any transition between hose liner and fitting; suitable for pigging

... and more: www.contitech.de/ih

26 · BBII 1/2008

1. The valve seat sealing

2. The guard ring electrode

3. The pre-mounted membrane

The valve seat sealing of the goldcathode into a saphire body with a high predetermined spring loadnot only eliminates internaI oxygenleakage, making zero settingsuperfluous, but also permits thehot caustic cleaning of the sensor.The expansion over the tempe-rature span of nearly 100° C is taken up by the spring, withoutdeforming the soft, pure goldcathode.

The guard ring electrode, havingthe same potential as the cathode,eliminates the oxygen present in the electrolyte. The cathode,therefore, only measures oxygenpenetrating through the membranedirectly above the cathode, and with ultra fast response. The pre-mounted membrane(patent pending) limits pressureshock and temperature effects.

These three features combinedprovide the following benefits:

– Perfect linearity from 0.1ppb to 200 ppm

– High sensitivity with a simple, single-point (no zero calibration required)

– Fast stabilisation and response time

– Sensor resists pressures up to 100 bars

– Sensor resists daily hot causticcleaning

Hach Ultra recently launched the latest development of the well-known, proven ORBISPHEREElectro-Chemical (EC) oxygensensors – the ORBISPHEREA1100 (picture 6). This newoxygen sensor now offers thesimplest sensor cleaning andrefurbishment whilst still providingthe most accurate oxygenanalysis.

Sensor refurbishment now takesno more than 3 minutes with a pre-filled recharge cartridge(patent pending). Cleaning andpreparation requires no technicalskills and no chemicals. Thanks to the smart chip storing thecalibration parameters, the sensorcan be calibrated in the laboratoryand made available as a “Plug and Play” device for the processoperator.

The ORBISPHERE A1100 sensor’sunique design allows extendedperiods between recharges; itsrobust stainless steel constructionmeans that it can be used in themost demanding applications,including resistance to CIP and pressures up to 100 bar.This latest development ensuresunrivalled accuracy and fastresponse time to detect processchanges.

ConclusionWe have seen that accurateoxygen analysis in the brewingprocess leads to improved shelf life and quality. Each step of the process was examined to understand the influence of oxygen and how to best applyvarious solutions for makingmeasurements. The mostwidespread dissolved oxygensensors employed by breweriesare electrochemical sensors. Hach Ultra ORBISPHERE oxygensensors are of this type.

Furthermore, the companyrecently launched an improvedORBISPHERE A1100 oxygensensor, which now offers thebrewing industry the simplestsensor cleaning and refurbishmentavailable whilst providing the most accurate oxygen analysis.

The application know-how andtechnological improvementsprovided in this article will lead to improved oxygen measure-ments for the brewing industry. M

Picture 6: Orbisphere A1100 Oxygen Sensor.

Picture 4: Orbisphere 3625 Total Package Analyser.

Picture 5: The Hach Ultra Orbisphere oxygen sensor.