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Oxygen Measurement in Brewing Process

The main ingredients of Beer

Cereal grains: Barley is more often used. Malt is obtained from the cereal grains after a process of g e r m i n a t i o n u n d e r controlled conditions.

Yeast: added to the wort and is responsible for producing alcohol in beer through fermentation.

Hops: the “spice of beer”,this plant contributes to the bitterness, aroma and flavour of beer and to the formation of a good froth. It also protects the beer against contamination by microorganisms.

Water : as t he ma in ingredient of beer, water quality plays an important role in determiningthe final taste of the beer.

Beer is the product of the alcoholic fermentation by yeast of extracts of malted barley. Whilst malt and yeast contribute substantially to the character of beers, the quality of beer is at least as much a function of the

Brewing ProcessMilling and Mashing: Barley is first steeped in cold water for 45 to 72 hour and is then placed in slowly revolving drums or in shallow tanks equipped with plows. As the wet grain is stirred and aerated, it begins to germinate. Germination is allowed for about 6 days to obtain sprouted barley, called malt: this operation is called malting

The Malted grain must then be milled to obtain relatively fine particles (coarse flour) in order to have a rapid extract ion and conversion of the malt components. The particles are then intimately mixed with hot water in a process called mashing to obtain wort of a suitable composition for the kind of beer being produced (varying times, temperatures and PH). Mashing lasts 2 to 4 hours and finishes with a temperature of approximately 75 ºC.

After mashing, the liquid portion of the mash, known as wort, is recovered: the whole volume is filtered in order to separate the spent grains from the wort itself. This is done by passing water through the mash at the right temperature in a filter press or lauter tun, which lasts around 2-3 hours, conducted at a temperature of 75-80 ºC.

Cooking: the wort is then run to the kettle (sometimes known as the copper, even though they are nowadays fabricated from stainless steel) where it is boiled to kill any bacteria that could infect the culture. Hops are added at this stage. The purpose of boiling is to transform and make soluble the bitter substances in the hops.

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Oxygen Measurement in Brewing Process

Why measure O2 in Brewing process ?

Oxidat ion in some processes can cause a change in taste, shelf life and clarity of beer.

Correct O2 level is r e q u i r e d f o r fermentation.

After fermentation air leaks at transfer points can al ter the beer quality.

Expected O2 levels in brewing processWort 5-15 ppm

Fermentation < 10 ppb

Filtration 5-150 ppb

Bright Beer after filtration 10-200 ppb

Beer at filler 20-200 ppb

Package dissolved O2 (bottle) 30-250 ppb

Package dissolved O2 (can) 20-120 ppb

Total package dissolved O2 50-450 ppb(can) 20-120 ppb

Total package dissolved O2 50-450 ppb

After boiling, it is necessary to separate the precipitated protein and the insoluble hop components from the hot wort. Separation may be carried out in a decanter using gravity or with centripetal force in a "whirlpool". Before the hopped wort goes into the fermentation tanks, it is cooled to a temperature of around 9 ºC and aired in sterile conditions.

Fermentation: the wort sugars are converted by the transformation of yeast into alcohol and carbon dioxide. Fermentation begins when yeast is added to the cooled o x y g e n - s a t u r a t e d w o r t . Fermentat ion takes place at controlled temperatures and lasts around 7 days. At first it is quite violent, then it slows down gradually until the yeast is deposited on the bottom of the tank. Fermentation is complete when the desired alcohol content has been reached.

Maturation (aging): the beer is then matured by several weeks of cold storage, prior to filtering: it is a l l owed t o r es t a t su i t ab le temperatures in order for the undesirable volatile components, which might affect the f ina l «bouquet» of the beer, to be released. Often, when it is fully matured, a small amount of fresh wort or sugar is added, and the beer is placed in pressure tanks for final fermentation.

Clar i f ica t ion and bot t l ing: clarification is the operation that gives the beer its clear limpid quality, eliminating the last remaining traces of clouding still in suspension. It consists of pumping the liquid through a suitable filter. The filtered beer is then stored in tanks and ad jus ted to the requ i red carbonation, and is then ready to be bottled.

Oxygen and Carbon Dioxide Control

During mashing and lautering: during this process, Oxygen is introduced to the wort after boiling, and prior to the addition of yeast. Already at this early stage, oxygen uptake has adirect influence on turbidity and color as well as on the quality of bitterness. Typical O2 levels vary from 10 to 16 ppm.

During fermentation: dissolved oxygen level plays a very significant role in the success of fermentation. Any excess or def ic iency is detrimental to the gravity, clarity, color and taste of the final beer. Determining the amount of oxygen or air to inject for fermentation can be tricky.

Too little dissolved oxygen results in: - Low and sticky fermentation- Off flavours- Poor yeast crop- Low ester/ alcohol production

Too much oxygen causes:- Rapid fermentations, resulting in excessive yeast growth and beer losses- High ester production, resulting in a fruity-tasting beer

Without a good dissolved oxygen meter, it is impossible to gauge, and therefore control the amount of oxygen in your wort. A good o x y g e n a t i o n s y s t e m s h o u l d therefore include a measuring instrument locate at a reasonable distance from the injection point in your process. quality, eliminating the last remaining traces of clouding still in suspension. It consists of pumping the liquid through a suitable filter. The filtered beer is then stored in tanks and adjusted to the required carbonation, and is then ready to be bottled.

Dextens SA - Ch.des Aulx 181228 Plan-les-Ouates - SwitzerlandPhone: ++41 22 884 83 06Fax : ++41 22 794 66 65E-mail : info@dextens.ch - www.dextens.ch

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Oxygen Measurement in Brewing Process

Solubility of Gases in Water100% oxygen @ 1 bar & 0°C +/- 70 ppm

100% nitrogen @ 1 bar & 0°C +/- 70 ppm

100% carbon dioxide @ 1 bar & 0°C +/- 3370 ppm or 3.37 g/kg or 1.7 V/V

Typical Gases in Package

Dissolved Gases:

- 2 to 3 V/V CO2 or 4 to 6 g/l- 1 to 2 ppm N2- 0.1 ppm O2

Headspace Gases:

- 97 to 99% CO2- 1 to 2% N2- 0.5 to 1% water vapor- 0.01 to 0.1% O2

Carbon dioxide revovery: CO2 is a d e r i v e d p r o d u c t f r o m t h e fermentation process. CO2 can be recovered during fermentation and then injected again in carbonization process. To be recovered CO2 must contain very low O2 concentration, as the oxygen concentration can significantly affect the dissolved oxygen level in the final beer. Measurement and control of oxygen are therefore required to maintain a q u a l i t y p r o d u c t w i t h o u t unnecessar i l y wast ing la rge amounts of carbon dioxide. The sensor can be installed into the pipe at the top of the fermenter: the CO2 can be switched off when a specific limit is reached (50 ppm oxygen).

After Fermentation

At the end of fermentation, the beer should be almost completely free of oxygen (less than 50 ppb). Beer is transferred from aging & storage tanks to packages. At this point, the beer is highly susceptible to oxidation, which has the following effects on the end-product:

- Undesirable taste- Cloudy/ hazy beer- Increased beer astringency- Darkened beer colour- Beer shelf-life

In addition to the mentioned required O2 measurements, some processes need a strict oxygen level monitoring throughout the brewing process:

Water deaeration: Degassed water is used throughout the brewery to reduce oxygen levels in filters, t a n k s , a n d l i n e s . D O 2 concentrations must be kept as low as possible (usually < 20 ppb)

Transfer points, filler

Transfer points such as filters, coolers, pumps and before the filler are the most important measuring points to detect air leaks. Oxygen concentration must be measured at several point of the brewing process with sensors directly installed in the process. Typical oxygen concentrations should not exceed 50 ppb.

CO2 Recovery

During fermentation, the wort sugars are conver ted by the transformation of yeast into alcohol and carbon dioxide. CO2 can be recovered to be used later on in brewing process (carbonator), but must be very pure. Air is trapped in foam and dissolved N2 is slow to be removed from the wort. O2 sensor signals the purity of the recovered CO2.

CO2 purity can be measured by the O2 concentration:

- 99.9% CO2 = 0.1% impurities = Air = 20% O2 + 80% N2--> O2 = 0.02% = 200 ppm

- 99.99% CO2 = 0.1% impurities = Air = 20% O2 + 80% N2--> O2 = 0.002% = 20 ppm

Dextens SA - Ch.des Aulx 181228 Plan-les-Ouates - SwitzerlandPhone: ++41 22 884 83 06Fax : ++41 22 794 66 65E-mail : info@dextens.ch - www.dextens.ch