Do Coffee Bags "Lock in the Flavour" ?

The test will be posted in a few phases, perhaps more if there are leakage problems around the valve, such as the testing apparatus, results, and implications of the findings.

To the left is the inside part of a Check Valve that is incorporated on many coffee bags.  It permits the coffee roaster to bag the coffee very soon after roasting.

For those who may not be aware, freshly roasted coffee releases CO2 (Carbon Dioxide) in the days that follow the roasting session.  The pressure is sufficient to burst bags.  Initially the coffee was packaged in various media such as paper and consequently not hermetically sealed.  Some roasters "aged" the coffee and packaged it several days later when the CO2 had been dissipated.  The Check Valve is a more recent development which allows the CO2 to escape without splitting the bag.  There could be an advantage to this method if the valve is placed such that when the filled bag is stored the valve is the highest point of the bag.  CO2 is heavier than air therefore it will gravitate to the bottom of the bag forcing out the lighter air first.  Technically it is possible that all the oxygen could be forced out in this way.

The purpose of this test is to verify the premise that the Check Valves are more important to the marketing campaigns than to preserve coffee or "locking in the flavour".  Does a valve costing about a penny do the work of precision devices?  If the bag is not hermetically sealed the constantly changing atmospheric pressure will make the bag "breathe" which will introduce oxygen to the contents. 

The apparatus is quite simple and will involve measuring a Control to be certain that the test equipment is leak proof.  The upper left barbed fitting will be connected to a vacuum pump then the valve will be closed.  The Needle Valve is rated at 6,000 psi therefore it should not be harmed by this test.  The vacuum will be measured by water movement in a U tube.  The picture shows two devices that can be sealed to the bag.  The preferred socket is the one to the right which is machined with steps that will fit just over the valve so that it is not distorted or twisted.  This is better than in reality where the valve is pushed by the beans.  Several different sealing materials may be required before a good seal is established between the socket and the plastic check valve.

Plotting the height of the water column should be a good indicator of the leakage rate, if present.

Marketing departments are notorious for making unsubstantiated claims.  Rather than admit error the trend is to spend more money to embellish their fabrication.  Let's check the foundation to the claims.

Freshly roasted coffee does its own marketing.

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The first phase is Testing the bag's Venting Valve in Ideal Conditions.  

The venting valve was cut from a new bag (unfortunately that is a sacrificial test) but a lots of material was left on either side of the valve.  The valve was then mounted to the socket and sealed with a thin layer of silicone adhesive on the periphery.  The adhesive cured overnight. 

A slight vacuum ( 33.5" H2O or 851 mm of H2O) was drawn against the valve.  That is P1-P2 = 67" H2O (1.702 m) in the U tube manometer.

After an hour the water column was 1" (25.4 mm) lower which represents 1.81 cc of water.

After an 2:45 hours the water column was 1.5" (38 mm) lower which represents .165 in3  (2.7 cc) of water.

After an 6:00 hours the water column was 3" (76.2 mm) lower which represents .33 in3  (5.43 cc) of water.

After an 47:00 hours the water column was 9.25" (235 mm) lower which represents 1.022 in3  (16.74 cc) of water.

After an 70:00 hours the water column was 9.88" (251 mm) lower which represents 1.091 in3  (17.89 cc) of water.

Granted the Control Run has not been done.  Under ideal conditions it is little leakage but then it is over a short period.  The pressure, however, is considerably higher than the barometric fluctuations.  So far it can be established that it is not a hermetic seal.  To reflect the packaging role the pressure may have to be reduced, the time period increased, and the valve will have to be pushed against beans rather than held flat in a socket.

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More on a newer blogs Vented Bags Revisited  and Packaging - Optimism