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Full Text Searchable PDF User Manual
Quick Guide for using a 1-CUBE GMA Dissolved CO
for Beer and Cider
Also read the User’s Guide
To start measuring the dissolved CO
in a sample, first take a sample from a tank as follows:
It will help if you watch this YouTube video:
1) Direct the outlet hose to a suitable drain or waste beer collection container
2) To clean any debris from inside the tank outlet valve, open the tank sampling valve. Allow
beer to flow out to waste for a short time. Close the tank sampling valve.
3) Connect the inlet hose to the tank sampling valve. If necessary, secure with a clip or cable tie to
achieve a gas tight seal. Remember to allow for the pressure in the tank, it will be applied to the
4) Fully Open the tank sampling valve and Fully Open the GMA inlet valve
5) Gently Open the GMA outlet valve until beer starts to flow. Adjust the outlet valve until a slow
and steady flow is achieved to flush through and fill the chamber with new beer. Normally allow
the beer to flow for at least 30 seconds, and until the beer flows clear in the chamber.
6) Fully Close the GMA outlet valve. Then Fully close the inlet valve.
You now have your sample for analysis with the instrument, but the beer in the chamber is under
pressure, notice the gauge. This excess pressure must be released, otherwise our equilibrium pressure
reading will be wrong.
7) Open the outlet valve for a short time (about 1 sec.) Close the valve. Excess gas will have
released. The pressure should now be about zero or just above.
8) Rotate and unlock the black plunger on top of the GMA, so that the plunger can move up &
down. Notice the position of the white dot and the locked position.
9) Fully lift the plunger and push down hard, repeat for THREE full strokes in quick
succession. (Only three times. No more and no less!). NOTE: On each stroke you will see gas
being released from solution inside the chamber.
10) After the third down stroke rotate and lock the plunger
11) In theory partial pressure equilibrium has been reached. Notice how the pressure in the chamber
has increased. This is because dissolved gas has come out of solution.
12) Switch on the digital thermometer and read the temperature.
13) Read the pressure in kPa
14) To calculate the dissolve CO
content, line up the pressure and temperature on the rotary
nomogram on the base of the instrument. Read off the CO
content in g/l
NOTE: 1 g/l = 0.506 %vol. 1%vol = 1.976 g/l.
To measure another tank, re-connect the GMA and repeat the steps above. The new beer sample
will push out the previous beer.
Continued…please read on, cleaning is important!
Note the inlet tube
Finally REMEMBER TO CLEAN the GMA after each session.
1) Connect the inlet hose to a clean cold water supply (Max. pressure for GMA: 4 bar g).
2) Flush through by opening both inlet and outlet valves, with water flowing to drain until the
chamber is clean. REMEMBER to unlock and pump the gas release plunger several times to
avoid the piston becoming stuck with dry beer. Relock the plunger.
If the plunger does become stuck, unscrew it and soak it in warm water until it frees.
3) Disconnect the water supply, with the valves still open. Lift the inlet hose and lay the
instrument on its side so the water drains out via the outlet valve. Finally, turn the instrument
upside-down to drain the last few drops.
4) Close the valve gently and store the unit upright until it is next required.
Normally cold water is sufficient for cleaning. In severe cases warm water (max. 25°C) or dilute 0.5 to
max. 1% acetic or peracetic acid or hydrogen peroxide can be used at ambient temp. The GMA has
brass valves, so do not leave them soaking or in contact with sanitizer for longer than is essential.
Finally, washout thoroughly with clean water.
Max. Temperature: 25°C. Max. Pressure for GMA: 4 bar g. (notice the gauge limit!)
GMA construction materials: Chamber: PVC-U, Pump: Stainless Steel, Valves: Brass, Hoses: Silicone
Just as with other more expensive instruments in the market, the dissolved CO
result is a calculated value
based on the measured pressure and temperature values. The calculation formula describes detailed
observations and measurements of a physical behaviour. It was first defined in 1803 by Dr William Henry, as
‘Henry’s Law of Partial Pressures’. The mathematics are very complex. Over the years numerous learned
people have developed and improved various different formulae. Nevertheless, none can give us an absolute
and 100% true value. Variations between different instruments and different ‘measuring’ methods are normal
and must be expected.
For best results, a good understanding of the physical behaviour and a consistent operating procedure are
essential. With this, reliable temperature and pressure measurements should be achievable. Attention should be
given to achieving both temperature stability and true partial pressure equilibrium, which is not as quick or easy
as one might think. For example, the temperature of the equipment, the operating environment or the operator’s
hands will adversely affect the beer temperature and thereby the pressure. They both influence the gas
solubility. Ideally and before testing starts, the instrument should be at exactly the same temperature as the
beer. Even the shortest exposure of the beer to air will reduce the dissolved CO
content, this is especially
significant when testing kegs. The smallest of opening in pipes and seals will allow CO
gas out and O
even though a beer leak might not be seen
We hope you enjoy making great beer, helped a little by your new 1-CUBE instrument.
There is more equipment for brewers on our websites.