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Master Brewers Association of the Americas > BREWING RESOURCES > Ask the Brewmaster > Posts > Measuring dissolved Nitrogen in beer
October 14
Measuring dissolved Nitrogen in beer

​Q:  As a very small brewery we don’t have an analytical capability to measure ppm of dissolved gases.

 The best I have is a Zahm & Nagel for CO2. Other than that, I rely on the Mark I eyeball!

 Any help you can find with respect to *process* from the N2 cylinder regulator, through the “carb” stone and to the head pressure gauge, along with temperature and time would be most appreciated.

A:  A cheap and cheerful way to measure N2 in beer is possible.  It does require a Zahm head space buret and caustic reservoir as well as a bottle piercing device and stainless steel standard sample bottle.  These are all a lot let expensive than a digital device and can be used for other tests like carbonation and head space airs as well.  In answering this question I tapped into the knowledge of Gil Sanchez of Sierra Nevada Brewing Co., Jim Hackbarth retired physical chemist of the Gambrinus Company and BridgePort Brewing Company colleague David Gillibeau for the following process and calculations.

 To dissolve N2 gas into the beer:
·         Perform this process only using a beer tank that is ASME rated for 30 psig (2 bar) or higher and is fitted with tank overpressure safety valves
·         Add nitrogen to the pressure rated bright beer tank through inline recirculation or a sintered stone in the tank
·         Build 23 pisg of head pressure on the tank

·         Vent tank slightly to continue adding N2 gas
·         Measure ppm of dissolved N2 and continue the process until 50 ppm dissolved N2 is reached
 
Measure dissolved N2 using the Zahm head space air buret:
·         Using a crowned Zahm stainless steel sample bottle collect a 12 oz (355 ml ) sample from the tank zwickel

·         Warm the sample in a 70F (20C) water bath for 5 minutes and bring up to temperature
·         Shake the sample in an ultra sound or by hand for one minute

·         Pierce the crown in a Zahm piercing device
·         Using standard head space measurement procedures dissolve the carbon dioxide from the sample in the head space buret with caustic until the pressure stops increasing
·         Invert the buret until a stable bubble is formed.  This will be Nitrogen gas.
·         Read the volume of the bubble in millimeters
 
Calculations:
A fairly accurate method of calculating the ppm of dissolved Nitrogen gas in the beer can be made using the following equation:
 
(mLs x Wt. N2 x 2.82)/24.1
 
Where:
mLs is the size of the bubble in the Zahm buret in mLs N2/355 mL sample
Wt. N2 is the formula weight of Nitrogen (28 grams per mole)

2.82 is factor converting sample size and conversion units

24.1 is the molar volume adjusted to room temperature (70F) given in moles per liter
 
Example for a reading of 10 mLs on the Zahm buret:
 
(10 ml N2/355 ml beer)x(1000 ml beer/liter beer)x(1 liter N2/1000 ml N2)x(1 mole N2/22.4 liter N2)x(28 gm N2/mole N2)x(1000 mg N2/gm N2)
 
After canceling out units, we have
(10 x 1000 x 28 x 1000)/(355 x 1000 x 22.4) mg N2/liter beer = [10 x 28 / 22.4] x [(1000 x 1000)/(355 x 1000)] = [10 x 28/22.4] x [2.82] mg N2/liter beer
= 35.25 ppm dissolved N2

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