Do You Save Your Nitrogen for Modified Atmosphere Packaging (MAP) at Home?

[Jon S]

I've always wondered if the folks who use liquid nitrogen at home ever considered using it to try and displace oxygen in their packaging of food/ingredients.

 

Let's say you were about to put away some left overs (vacuum sealed or not), would it make sense use nitrogen gas?

My thinking is: if you have to the vent your dewar anyway, could you collect the gas vented and use it later for this purpose? 

[btbyrd]

Dewars are self venting so there’s not a separate venting process from which you could glean some surplus nitrogen gas. It’s hard to dish out just the gas phase of nitrogen if all you have is a dewar, and since the gas is invisible, it would be difficult to know that you’ve done it correctly.

I know that Dave Arnold’s bar crew at the now defunct Existing Conditions  used liquid nitrogen to exclude the air in the headspace of bottled cocktails before capping them. It only takes a dash, and a dash of LN is many more times the amount than you actually need of gaseous nitrogen (which is like 900 times less dense than than its liquid phase).

I guess you could add a splash to an airtight container with food before sealing it and wait for the nitrogen to fully sublimate, but you run the risk of freezing some of your product. Honestly, I’d rather use one of those valves containers designed to use with vacuum machines than try to recreate gas flush with LN. 

[C. sapidus]

31 minutes ago, btbyrd said:

I guess you could add a splash to an airtight container with food before sealing it and wait for the nitrogen to fully sublimate, but you run the risk of freezing some of your product. Honestly, I’d rather use one of those valves containers designed to use with vacuum machines than try to recreate gas flush with LN. 

 

Liquid nitrogen (LN) expands about 750x when it turns to a gas. This why LN containers are always vented. If you put LN into an airtight container, the 750x expansion of LN to gaseous nitrogen can cause the container to over-pressure and explode.

 

It sounds like you understand the risks, but for the benefit of others: I would advise against putting LN into an airtight container. Could it be done safely? Yes, but the consequences of a mistake could be severe.

 

It is also important to have good ventilation when working with LN to avoid creation of an oxygen-deficient atmosphere.

 

One can buy cylinders of gaseous nitrogen. This would be a much safer way to create an inert atmosphere, should you wish to do so. But wouldn't vacuum sealing accomplish the same thing?

[gfweb]

Ditto the risks of LN2 in a sealed chamber.

 

But N2 in a vacuum sealed bag would be gone with all the air after sealing.

 

Could you put a little LN2 in a bottle filled with food...just enough to fill the headspace?  I suppose, but the cap must be air-tight.

 

Assuming the food in the bottle wasn't made at canning temperatures, you would run the risk of botulism in that anaerobic environment.

[KennethT]

9 hours ago, C. sapidus said:

Liquid nitrogen (LN) expands about 750x when it turns to a gas. This why LN containers are always vented. If you put LN into an airtight container, the 750x expansion of LN to gaseous nitrogen can cause the container to over-pressure and explode.

 

It sounds like you understand the risks, but for the benefit of others: I would advise against putting LN into an airtight container. Could it be done safely? Yes, but the consequences of a mistake could be severe.

 

It is also important to have good ventilation when working with LN to avoid creation of an oxygen-deficient atmosphere.

 

One can buy cylinders of gaseous nitrogen. This would be a much safer way to create an inert atmosphere, should you wish to do so. But wouldn't vacuum sealing accomplish the same thing?

The problem with vacuum sealing is the direct bag contact with some foods like fresh fruits and leafy greens. Using a nitrogen flush, you can use a rigid container that will not contact or squeeze the contents but also get rid of excess oxygen.

[Bernie]

One technique I have used to replace air in sealed electronic components is to use gaseous nitrogen, a largish vacuum cleaner and a large plastic bag.

You put the component in the bag and fill the bag with nitrogen. Then vacuum all the air out until the bag collapses. Refill with nitrogen and repeat.  You can reduce the amount of oxygen significantly, but I guess you don't get it all out. (most likely is reducing it from ~20% to lass than 1%)

I guess you could adapt something like a food saver type vacuum sealer to do the same thing, have the bag with an inlet with a valve to nitrogen, go through the process of vacuum and refill with nitrogen a few times, seal the bag with it inflated then disconnect the nitrogen leaving the valve on the bag, then do a do another seal with the valve inside the machine, then just cut that part of the bag with the valve.

It would be a bit fiddly but could be done.

Be aware that all nitrogen in bottles IS NOT food grade. It will have other gases mixed with it. In fact most nitrogen used in  industrial processes will have different percentages of gases (usually inert) specified.

Best to use medical grade nitrogen, or if it is only to remove oxygen then  carbon dioxide can be used.

Carbon dioxide has the advantage that it is heavy so concentrates in the lowest point of the container, and it is readily available in frozen form (dry ice)

[Bernie]

3 minutes ago, KennethT said:

The problem with vacuum sealing is the direct bag contact with some foods like fresh fruits and leafy greens. Using a nitrogen flush, you can use a rigid container that will not contact or squeeze the contents but also get rid of excess oxygen.

You could use the technique above with the dewer/rigid container in a plastic bag. The hardest part would be extracting the air nitrogen mix completely. It may take several iterations to reduce the oxygen percentage.

Carbon dioxide in the form of sufficient dry ice is a much better alternative as you just put the dry ice in the bottom and vent the dewer at the top. Once the dry ice is melted you will have little oxygen.

[blue_dolphin]

22 minutes ago, Bernie said:

Carbon dioxide in the form of sufficient dry ice is a much better alternative as you just put the dry ice in the bottom and vent the dewer at the top. Once the dry ice is melted you will have little oxygen

Dry ice isn’t without hazards. It doesn’t melt, at least at atmospheric pressure, it sublimates: solid -> gas. In a properly vented dewer, all should be well, but don't think of putting dry ice into anything like a glass jar and think you’ll seal it up  once the solid CO2 is no longer visible because as it warms, the gas can move out of solution and BOOM!

[Bernie]

1 hour ago, blue_dolphin said:

Dry ice isn’t without hazards. It doesn’t melt, at least at atmospheric pressure, it sublimates: solid -> gas. In a properly vented dewer, all should be well, but don't think of putting dry ice into anything like a glass jar and think you’ll seal it up  once the solid CO2 is no longer visible because as it warms, the gas can move out of solution and BOOM!

That is why you need to vent it. Once the ice disappears, you wait till the temperature equalizes and provided the vent is at the highest point, the carbon dioxide will have displaced the air, since it is heavier than air it sinks to the bottom.

There is another hazard as well.

Carbon Dioxide is what actually triggers the  intake response part of breathing, so if you enter a atmosphere full of carbon dioxide it will cause you to intake breath and with no oxygen you will quickly succumb and pass out. It is very desirable if using carbon dioxide to make sure the room is actively ventilated to constantly mix and change the air.

[Jon S]

Let's say I affixed a normal balloon to the vent of a dewar and once "full" nitrogen gas I then poured that gas into an airtight-sealable container with leftovers in it. The hypothesis is: displacing the oxygen before sealing extends the food's life. Is that something someone here has tried?

 

The question is, if it does work, by how much is the improvement? Would it be a dramatic increase? Days vs weeks? Is botulism really going to occur in that time frame?

[KennethT]

Have you googled the title of this thread?  This comes up pretty high in the rankings and is quite informative - and seems to answer most of your questions:

https://www.industrialpackaging.com/blog/what-is-modified-atmosphere-packaging

[Bernie]

5 hours ago, Jon S said:

Let's say I affixed a normal balloon to the vent of a dewar and once "full" nitrogen gas I then poured that gas into an airtight-sealable container with leftovers in it. The hypothesis is: displacing the oxygen before sealing extends the food's life. Is that something someone here has tried?

 

The question is, if it does work, by how much is the improvement? Would it be a dramatic increase? Days vs weeks? Is botulism really going to occur in that time frame?

Nope.

Assuming you were able to fill the balloon, just pouring it into your container will not displace the oxygen, since oxygen is slightly heavier than nitrogen.

But it only slightly heavier so would take a long long time for the oxygen to settle to the bottom.

Pouring nitrogen into the container with food and air will dilute the oxygen content of the air.

Carbon dioxide on the other hand is heavier than both and quickly settles if not agitated. (it is why you need ventilation in a room when you use heating that produces carbon dioxide (or its more deadly brother carbon monoxide, the heat will cause convection currents will will keep the carbon dioxide/oxygen/nitrogen mixed)

[C. sapidus]

Liquid nitrogen (LN) is commonly used in biomedical research laboratories. LN hazards include extreme cold, oxygen deficiency, rapid expansion/pressurization, and oxygen enrichment. To work safely with LN, employees need training, personal protective equipment, excellent ventilation, and (in come cases) oxygen monitors and alarms.

 

I would guess that LN safety standards are less stringent in restaurants, food vendors, bars, and home kitchens.

 

And of course no one is eating LN in the lab. Fun fact: ingesting 30 ml of LN can perforate your stomach!

 

For more: A Qualitative Risk Assessment of Liquid Nitrogen in Food and Beverages (clicky). Quick summary: Food-related LN injuries are rare but often severe.

 

One of the standard recommendations for LN is to wear loose-fitting cryogenic gloves and pants without cuffs. Anyone who does not understand why should not be handling LN.

 

Please keep yourselves and your guests/customers safe.