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<pre>I have been trying to get some clarity about the dynamics of the process of
replacing the air with Nitrogen.

What I understand is that air consists of roughly 80% Nitrogen and 20%
oxygen, if we ignore some other minor constituents for the time being. It
is just a mixture of gasses - the molecules of nitrogen and oxygen float
about randomnly, they are not locked into some kind of structure or lattice.

If one fills an amount of air and an amount of nitrogen into a space, the
air and pure nitrogen will not be separated into two layers. Whilst there
may be an initial concentration of the one or other in specific areas due to
the point of entrance into the volume, in time the molecules will totally
intermix. In effect, what you will have is a mixture of nitrogen and oxygen
that has an oxygen content lower than that of air.

It is probably possible to achieve a reasonably low oxygen concentration by
introducing nitrogen at one side of a container (at a slow flow-velocity)
and venting at the other, i.e. the gas flow (wash) in the container will be
from the one side of the container to the other, and if the process occurs
reasonably quickly, there will not be enough time for the gasses to be fully
mixed up, and a comparitively low concentration of oxygen can be achieved.

Ideally one would want to evacuate all air from the container before filling
it with nitrogen, but this is not practical as the tank would have to be a
full-on pressure vessel if it is not to collapse. Another would be to
completely fill the tank with a liquid and then drain it again, ensuring
that the headspace is sealed off from air and only nitrogen is filled into
the headspace. But what liquid would you use? You can't use water.

I have been told that in the wine industry 2% oxygen in the headspace above
the wine in a bottle is considerd acceptable after purging the bottle with
nitrogen before filling.

If you are serious about this you should consider getting a oxygen tester.
You get hand-held instruments with a digital readout that give you the
concentration of oxygen in a gas. You need to make provision for a small
access hole to the headspace of your tank to insert the probe needle -
opening a big hatch to take the sample could be counter productive. Ideally
you would permanently fit a probe into the headspace of each tank and seal
them off. Don't know what all this would cost.

All the above is information scrapped together and some personal deductions
that may be quite wrong - I stand to be corrected.

Kurt Küpper




-----Original Message-----
From: agonis@highway1.com.au [mailto:agonis@highway1.com.au]
Sent: Thursday, 25 October 2001 02:26
To: OliveOil@yahoogroups.com
Subject: [OliveOil] Re Nitrogen Blanket


I am not a science graduate just a mere small grower and processor
however I have done a little research into the nitrogen blanket
senario and been reliably advised that nitrogen gas is in fact
lighter than air (albeit only very slightly) and as such will not lay
on the surface of an oil body as the word "blanket" would suggest.

The advise to me was that the gas should be introduced to the top of
the headspace of a sealable oil container, a vent pipe is lowered to
just above the surface of the oil to allow the air to be purged out
by the incoming gas, when a volume of gas at least equal to the
volume of the headspace has been introduced the vessel is then
sealed. When oil is drawn off the head space must be vented and then
nitrogen replenished in relation to the volume of oil removed. I
use a gas regulator calibrated in litres per minute to calculate the
volume of gas being injected. This may not be the most scientific
way of doing things but appears to work for me. I would welcome
hearing what other producers are doing.

Michael Pimm





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