Why of-the-shelf coffee packages (available e.g. in supermarkets) are covered with aluminum (or some sort of hard silver a little bit shiny thick foil) from the inside?
I used to think this was just a marketing exercise (when it was applied to crisps/potato chips in American-Speak) but it's to do with it's excellent properties for keeping things fresh and sealing properties.
If we look at the Key features from this site:
Aluminium foil in packaging helps keep foodstuffs fresh for months without refrigeration.
With the outstanding barrier properties and contributions to the sealing process, aluminium foil guarantees the excellent material and filling performance of aseptic and retortable packaging for milk, juices and soups.
- It prevents the contents from losing nutritional value, vitamins or aroma and gives total protection against light, moisture, oxygen, foreign matter contamination and damage.
This is why it's predominantly used in food packaging and not just for coffee packages, the foil is essentially a barrier to the outside environment to stop the beans from being exposed to oxygen and light, although some carbon dioxide gas will build up, there is a relief/degassing valve to allow this to escape
Light is the main consideration here, I assume. At least, for coffee.– MTSanApr 25, 2017 at 21:30
The main consideration is more likely oxygen - there are plenty of other packaging options that block light, but foil is particularly effective as an oxygen barrier, and "off-the-shelf" coffee has/needs a much longer transit-time/shelf-life than brown-paper-sack local roaster fare. Thus, metal cans or foil bags.– EcnerwalApr 26, 2017 at 2:45
@Ecnerwal good point will update– EdChumApr 26, 2017 at 8:09
The bags use a Mylar lining that protects from light, oxygen, and moisture.