As you were able to learn under "What determines the shelf life of staple food?", you can establish an oxygen-free environment for your staple food which is to be preserved in a relatively uncomplicated manner with the help of oxygen absorbers and therefore, take one of the most essential factors into account for maximising the shelf life.
Now of course several questions arise regarding the application of O2 absorbers.
"How many absorbers do I actually need?"
Let’s take a look at the following two facts in order to determine this:
Air is composed of approx. 78% nitrogen, approx. 21% oxygen and 1% of other gases.
Oxygen absorbers are available in various sizes / with different capacities (e.g. 500cc absorbers have a minimum intake capacity of 500cc, i.e. 500ml of oxygen).
An empty (except for air) container with a holding capacity of 500ml has approx. 100ml of oxygen according to the percentage of oxygen known to us which is approx. 21%. If we want to extract it, we would have to put at least one absorber at 100cc each or two absorbers at 50cc each into the container.
In principle, a 500cc or larger absorber could also be used. That wouldn't be a problem but maybe a waste. Incidentally, the actual capacity of oxygen absorbers exceeds their specified performance. So there is a built-in buffer, if for the mere reason that they lose a part of their effect until they are finally in the sealed container. Even if the percentage of oxygen in the air constitutes more than 20%, 100cc is sufficient in this case. However, in the case of doubt - e.g. if processing is more time consuming than expected – use one absorber more as a precaution, better one too many than one too few. After all, it is much more important to bind the oxygen completely than to save using a few absorbers!
"Ok, but how do I know how much air is in a container filled with wheat for instance?"
Due to the fact that we do not want to extract oxygen from empty containers but rather from containers filled with staple food, it is of course interesting to know, how much residual air is still in a container which has been filled with wheat for example.
For the determination, it is best to take a small receptacle with a known holding capacity, e.g. a cup with 250ml. Now I fill the cup with wheat to the rim, then I carefully pour water into it – also all the way to the rim. Now, if I pour this water into a measuring cup (possibly with the help of a sieve), I can see how much water fits into a 250ml cup with wheat. It is about 90-100ml, approx. 37.5%. Of course, air finds just as much room between the wheat grains as water does. So we can record that a container filled with wheat still has 37.5% of its volume in air!
If I completely filled a 30l container with wheat for example, I would in turn have to extract 11.25l x 21% = 2.36l of oxygen at an air percentage of 30l x 37.5% = 11.25l. In this case, I would be on the safe side if I used five 500cc absorbers or e.g. one 2500cc absorber.
To simplify matters, you can of course do the math using a 40% air percentage and 20% oxygen percentage.
If you repeat the above mentioned example with other types of corn, beans or rice, values of more or less 37.5% are also achieved.
Attention: In the case of noodles, especially macaroni or similar types of pasta, the percentage of air is of course significantly higher! In this case, please remeasure the air percentage again by yourself as described. In the case of articles of clothing or the like, you should, as a precaution, if applicable, assume the total volume of the container regarding the air percentage.
"And how do I know how many litres holding capacity an aluminium laminated bag has?"
For this, it is best to place the respective bag in a pail or a barrel with a known holding capacity. On the one hand this makes filling the bag easier and on the other hand I can now e.g. fill the bag to the upper rim of the pail / barrel and therefore, take the holding capacity of the pail or barrel as a basis, if I press out the remaining residual air as well as possible before sealing the bag. For this purpose, please also take a look at the photo show under "How to use aluminium laminated bags".
"How quickly do I have to process the absorbers before they lose their effect?"
Depending on the size, O2 absorbers are vacuum-packed in different quantities. As soon as you open this packaging, the absorbers start working. As described above, given that the O2 absorbers are especially equipped with a capacity buffer for this reason, you have a certain period of time at your disposal until they have reached their indicated capacity.
Opinions regarding the available time period vary. However, because you yourself can observe, during the appropriate application in a bag based on the obvious vacuum effect (also see photo show under “How to use aluminium laminated bags”) that the absorbers can have already done their job within a few hours, I would rather set a short time period of 20-30 minutes for the application. So, you should prepare everything so that you only have to provide all containers / aluminium laminated bags with the respective amount of absorbers and then seal them. Of course, it is easier to do this if someone assists you. For instance, while one person places the absorbers in the bags, the other person can start pressing out the residual air and begin with the sealing process
If you need more time (in case of small aluminium laminated bags or small absorbers, which are e.g. packed in units of 100 or 200) or if you are working alone, I would only take out and process several absorbers; store the rest in a hermetically airtight glass, like a preserving jar with a rubber ring and pressure cap for instance. By doing this, you can protect the absorbers for a short period of time (hours not days). In case of doubt, you may also use twice the amount of absorbers later. Basically, you should simply make sure that the absorbers “are not out in the open” any longer than necessary before using them for their actual purpose.
"Why don’t oxygen absorbers have to be packed in an aluminium laminated bag in an O2-secure manner?"
Indeed, that would be an advantage! However, because aluminium compound bags are not transparent, you would then no longer have a “freshness” indicator and therefore, in return a crucial disadvantage. For this indicator is attached on the inside and indicates whether oxygen has entered the packaging by means of changing colour.
"So according to this, the absorber vacuum packaging itself is not suitable for long-term storage?"
Correct. Over a longer period of time the packaging would let through a relatively large amount of air and with it, oxygen, due to the missing barrier (aluminium coating). The absorbers would therefore be used up piece by piece. If you use the absorbers within twelve months, you will have no problems, according to our supplier. Should you want to use the absorbers at a later period in time, you can of course also determine whether they are still “fresh” using the indicator (see next question). However, should you be planning to store the absorbers for several years in order to further use them at that point in time for containers / bags which have been opened by then, then I agree with you. The way they are packed, the absorbers are not suitable for that.
You may, of course, put your vacuum-packed absorbers into another oxygen-free aluminium laminated bag. This way you should be able to extend their storage life by far. However we can't assume a guarantee in this case.
"How can I recognise whether the absorbers are still “fresh” or have possibly lost their effect due to permeable packaging?"
An indicator attached on the inside changes its colour from pink to purply-blue when it comes in contact with oxygen. So, if this indicator is still pink, the absorbers are still active.
"Does it cause problems if I, as a precaution, use more oxygen absorbers as mathematically required?"
No. When in doubt, it is better to use more absorbers than not enough. If you use more absorbers than required, this does not have any negative effects.
"Are oxygen absorbers really harmless when they come in contact with food?"
Yes. Don’t worry. They are used to a great extent, particularly in the food industry, are equipped with a food safe PE coating on the outside and do not evaporate any toxic substances. They merely develop a small amount of heat during the reaction and release minor amounts of steam. The chief ingredient of oxygen absorbers is iron powder which reacts with the oxygen and therefore binds it.