Simple question: Why do diet milkshakes like Slimfast come in steel cans instead of aluminum like everything else? Is there something in these drinks that reacts poorly to aluminum? And aren’t all these cans lined anyway, so it shouldn’t make a difference?
In the case of carbonated drinks, some of the structural integrity is provided by the pressure inside the aluminium can, keeping it rigid.
Drinks without sparkle probably need tougher cans. That said, some carbonated drinks come in steel cans too.
Hmm. But I’ve also got some non-carbonated V8 juice that’s in the same kind of aluminum cans my carbonated soda comes in.
Those drinks might taste nasty if they are room temp or warm. Perhaps the thicker cans keep them cooler?
Aluminum itself is quite reactive, but the bare metal forms a thin hard layer of alumina (Al2O3) on exposure to air, and this layer is quite unreactive. Furthermore, anything that will react with aluminum is going to react with iron as well, only less vigorously so.
If I had to guess, I would say the economics of the manufacturing process drive the decision. It may simply be easier and cheaper to fill a steel can, or it may be that a heavier can is needed, as noted above, in which case the fact that raw steel is cheaper than aluminum may matter.
It could just be a matter of marketing. Maybe they’ve found that Slimfast sells better in steel cans—perhaps because, the cans being heavier, the contents are perceived as more substantial? But that’s a WAG for which I have no evidence.
If I had to guess I would have to think it’s the different amount of heat and pressure applied to make the contents safe for storage. Most diet drinks seem to be milk based, I can’t think of any other milk based canned product that is not in a thinker can or a glass bottle. Canned meats, tuna, spam all have stronger cans.
Drink cans have a thin coating of plastic on the inside anyway.
Aha - may be onto something here.
For several years, Slim Fast drinks were available in non-dairy fruit flavors (orange-pineapple, apple-cranberry-raspberry, etc.) in addition to the traditional dairy-based shake flavors (chocolate, vanilla). Non-dairy flavors were packed in aluminum cans, dairy in steel cans, driving home the difference in packaging each type of drink needs that you’ve pointed out.
Oddly enough, the canned Starbucks “double shot” drinks are packaged in aluminum cans despite using milk… not sure what’s up there.
There’s been a trend in the last few years for dairy diet/nutrition drinks to switch to PET bottles or aseptic Tetra Pak cartons, rather than steel cans.
Maybe, in the Starbucks case, the milk is already steamed to near-boiling and mixed with the coffee, just like it would be when ordering a regular latte/mocha, before it’s put into the cans, whereas the diet shakes are heat-treated after they’re canned? Just a WAG.
Also, coffee’s acidic nature is less conducive to bacterial growth (any acidic food is less favorable to bacteria, which is part of why you don’t have to refrigerate things like catsup and mustard).
I’ve wondered why Wittekerke (RateBeer link) is sold in steel cans, too.