What is better , a friend active in the beverage world asked, recycling aluminium cans or recycling glass bottles?
Neither, I immediately replied: always reuse, and never use aluminum. As the Dutch national environmental center reports: a deposit beer bottle is 8 x as environmentally friendly as a disposable bottle.
“Yes, but….” my friend reacted, with the usual denial and defense of his own assessment …
He is very environmentally conscious and had already experimented with a feed-in system and his own bottle ceaning installation, but that was too complex and labor intensive for a small producer. Moreover, after some discussion it became clear that there was no other option here, at least for the moment, it had to be recycling, because it was export, and bringing bottles back from overseas was not opportune.
Ok, so one-time use and recycling seemed inevitable in this case, is the assumption. I thought it would still be glass as the best option, but I promised to sort it out. For him, the preference was for cans, but for other reasons: can packaging takes up much less space, and transport would then be a lot cheaper. But he really wanted to know if it would be okay from an environmental point of view.
But it all starts with the basics: the ‘embodied energy’ of both uses. After all, everything starts with that: the energy comparison. Everything that happens in the world starts with an energy conversion, The process should energetically make sense, before looking into other (side-)effects. Energy related to material is currently our top priority, at least avoiding or limiting it. Regardless of which type of energy is used, even renewable energy: after all, wind turbines or solar panels also have to be produced and our material depletes, the less we need, the better.
I found a good study of a comparison between glass reuse and glass recycling for the wine sector in Italy. 
Regarding reuse, an energy intensive purification process is needed, at least at the industrial level. Reusing a bottle yourself at home probably requires a lot less, since the origin of the bottle is usually known, and reuse can sometimes be limited to just rinsing. But industrially the origin is unknown and all risks must be excluded, due to factors such as liability. Which costs energy.
But it was about recycling. What I did not expect is that a separate purification step is also required in recycling, before the glass goes back into the oven. This naturally increases energy demand.
With this study, see table (below), I derive at approximately the following figures:
recycling: 1 kWh per bottle,
reuse: 0.36 kWh / bottle
new: 0.9 kWh per bottle.
The 1 kWh applies to 1 cycle in recycling. Of course, part of the original embodied energy of a new bottle must be added to this, since this has not disappeared suddenly by recycling. And a portion of new glass is always added during recycling. In this case 42.5% (although there are also claims up to 80% recycled content and 20% new).
Next aluminum. It is a lot harder to find correct and reliable figures, although I have not spent days on that. These are some approximate figures:
A new can weighs around 20 grams, and with the general figure of 220 MJ./kg for primary production, that amounts to 1.2 kWh per can.
Recycling aluminum is still energy intensive, although a lot less, but the energy required for this is still in the order of magnitude of, for example, producing new steel. For the recycling of aluminum it is assumed that this is approximately 30 MJ / kg, or 0.17 kWh per can and 1-recycling turn excluding transport. Reuse of cans is not an option, so these are the approximate figures:
new: 1.2 kWh / can
recycled: 0.17 kWh / can
To make a complete comparison, a evaluation of the functional unit over time is needed: we take 1 year for that. In which 100 cans or bottles must be continuous available. For the loop time we assume 6 weeks (taken from a general average for deposit beer bottles). Of course, the recycling degree is also important. If it is not 100 pct, we will lose material that needs to be replenished with every cycle.
For aluminum we find the following figures: 200 billion cans of aluminum are produced in the world each year (!), of which around 100 million are recycled. That is very little, only 5%. The figures are considerably higher in Europe, for example. We assume 75% for aluminum, and 90% for glass that has an established recycling culture.
With 9 cycles the aluminum left after 1 year is only 7.5% , and with glass it is 38.7% However, with each cycle this is supplemented with new material for both. In total, the embodied energy for keeping 100 cans or bottles in a recycling circulation:
for aluminum at approximately 504 kWh.
For glass comes to around 1051 kWh per 100 bottles per year.
That is a clear difference in favor of aluminum. Surprising. But explained by the enormous difference in weight: from 225 grams and 20 grams, that is a factor of 10. And I come across reports that the cans could even go down to 15 grams.
This is not the whole story by the way. This only concerns the embodied energy comparison. There is also something like Circular energy, energy needed to restore the stock of raw materials, to really close the chain. It is very high for Metals, and if we include this (calculated in Embodied Land via the MAXergy method ) glass will be much better in all cases. However, that is not yet very common, and left out in this analyses for the moment.
I will also not go into other aspects here, such as water consumption in de the several processing steps, and the process of extracting aluminum from bauxite ores. Which also has some issues.
But, on the basis of this coarse energy analysis, in the event that recycling is the inevitable route, aluminum comes off well. Obviously check what the recycling percentages are, of the country to which you are exporting, to be able to make the locally correct comparison.
But I can reassure my friend, there is no need for (aluminium-) ‘can-shame’ (in this case).
This does not alter the fact that we still have to look for solutions to completely avoid single use of materials and products, even if they can be recycled. I do have such a discussion on my yearly sea sailing trip with friends …. Canned beer is the standard on sailing boats: it requires little space, and can be stowed away anywhere, and cleans up nicely if you have them finely squeezed afterwards for the waste bin. When I recently appeared on board with a crate of beer bottles, its glass and with deposit for reuse, there was a little uprise on the boat: how did I get it in my head to bring a crate of glass, where to go – the skipper- with that crate, no glass on board! , etc etc. I tried to argue saying that in the event of an emergency we could send out bottle mail, but that was only throwing oil on the fire. After a few days of sailing however, the tide began to turn, and we were able to reach an agreement: that a sailing yacht should standard be equipped with a beer crate compartment, in that case it might be an option …
 Landi D., et all, Analyzing environmental sustainability of glass bottles reuse in an Italian wine consortium Procedia CIRP 80 (2019) 399–404
 Closing Cycles: Circular Energy, the missing link, July 2017, Conference: Exergy, LCA & Sustainability, ELCAS-5 , Nisyros, Greece
see also www.maxergy.org