Why are Slim-Fast shakes in steel cans rather than aluminium?

August 29, 2009 4:38 PM

My lunchtime obsession has finally percolated onto Ask MeFi. The question that I ponder every day I have at my midday repast: Why are Slim-Fast shakes in steel cans rather than aluminium?

I've been drinking Slim-Fast shakes as one way to help lose weight. I've also been intrigued by the fact that their cans are made of steel and not aluminium. It surprised me as the last time I'd seen a steel can was long ago (one of my chores as a kid was crushing cans for recycling and part of that job was using a magnet to separate out the steel).

I've been trying to think of reasons: it can't be cheaper than aluminium because if it was, every Coke and Pepsi can would be steel as well one would assume. It's not as if the contents are under such pressure that a sturdy steel can might be needed. Corrosion? I'm stumped.

I have asked a question at Slim-Fast/Unilever's site, but it has gone unanswered for a month or so. My Google-fu (and Bing-fu) is apparently not great because if the answer is out there, I can't find it. So, I thought I'd ask the experts who know all!

(PS: I'm thinking there might be off-topic'ing about Slim-Fast's efficacy, their taste, &c., which is why I decided to be IUPAC-approved and use 'aluminium'. I figure that'll attract all the pedants and at least amuse the chemist in me.)

posted by Fortran to food & drink (27 comments total)

I wouldn't be terribly surprised if it was to give the can more heft. More weight adds to the perceived notion that the drink will be more filling and thus more satisfying. Please take my wild speculations with a big fat grain of low-sodium, low-fat seasoning.
posted by Diagonalize at 4:46 PM on August 29

I've actually wondered about this mainly because Ensure and Special K both have drinks out in plastic bottles now - which made me think that the marketing people are gradually pushing switching over to bottles either for recycling or easy carrying or something. The whole "drink that replaces a meal" thing is a much wider market these days - you might try googling in that subject area (check out diet and marketing and/or meal drinks) and see if there's more info from the advertising/marketing angle.

If you're really interested - paper letters get more attention these days because it means the consumer is really into the product. And usually get some sort of response. (From someone who used to be in Customer Relations and answered such letters!)

On the taste - all I can say is all of the meal-replacement-drinks I've ever tried are always better cold - the taste seems totally different with temperature.
And this is the kind of thing I end up wondering about over lunch sometimes myself!
posted by batgrlHG at 4:54 PM on August 29

I suspect it's because Slim-Fast drinks aren't carbonated. The pressure from the carbonation keeps aluminum cans rigid, until opened, helping them survive shipping. The steel Slim-Fast cans are much more rigid than aluminum cans, so the lack of carbonation isn't an issue. An aluminum Slim-Fast can would have to be much thicker, presumably to a point where aluminum is no longer cost-effective compared to steel.
posted by 6550 at 4:56 PM on August 29 [5 favorites has favorites]

(I also noticed a difference in canned drink taste versus bottle taste. But I think that might just be me - I'd need a blind taste test to be sure!)
posted by batgrlHG at 4:56 PM on August 29

These people might know.
posted by cjorgensen at 4:58 PM on August 29

Whilst standard beverage cans in the USA are all aluminium, in Europe a majority are made of steel. I've always assumed this to be because aluminium is more expensive, but probably it's more complicated than that and involves tax breaks and recycling initiatives. In any case, beverage can=aluminium is not universally true. Slim-Fast cans are not standard US beverage cans, so it seems to me that there is no particular reason for them to be made of one thing rather than the other; if they have a different manufacturing process the decision of what to make them out of might be different from the decision regarding standard aluminium cans.
posted by nowonmai at 5:13 PM on August 29

The pressure from the carbonation keeps aluminum cans rigid, until opened

I thought it was just that water isn't compressible if it has nowhere to go. The basic idea of hydraulics.
posted by codswallop at 5:26 PM on August 29

batgrlHG: "(I also noticed a difference in canned drink taste versus bottle taste. But I think that might just be me - I'd need a blind taste test to be sure!)"

No, I've noticed this too. Not sure if it's taint from the aluminium, or (more likely), an aeration issue (in the same way as wine tastes different when aerated).
posted by benzo8 at 5:36 PM on August 29

in Europe a majority are made of steel.

As of 2007, nearly 70% of beverage cans were made of aluminium in Europe, with an average overall recycling rate of 62% (and above 90% in Norway and Sweden).
posted by effbot at 5:56 PM on August 29

codswallop, it's the same as monocoque construction for aircraft, and it does gain strength from internal pressurization, which carbonation would provide.
posted by Chocolate Pickle at 5:58 PM on August 29

The pressure from the carbonation keeps aluminum cans rigid, until opened

I like that idea, but V8 comes in aluminum cans, and it isn't carbonated.
posted by 517 at 6:01 PM on August 29 [1 favorite has favorites]

6550 writes "I suspect it's because Slim-Fast drinks aren't carbonated. The pressure from the carbonation keeps aluminum cans rigid, until opened, helping them survive shipping. The steel Slim-Fast cans are much more rigid than aluminum cans, so the lack of carbonation isn't an issue."

This is a good possibility. Plain canned water used to come in steel cans even when all other drinks came in aluminum cans.
posted by Mitheral at 6:05 PM on August 29

I thought it was just that water isn't compressible if it has nowhere to go. The basic idea of hydraulics.

There's air in there too, which is compressed. Try shaking up a can (which forces more gas out of the liquid), and notice how much stiffer the can is.
posted by floam at 6:05 PM on August 29

I like that idea, but V8 comes in aluminum cans, and it isn't carbonated.

You can of course pressurize the container even if you don't fill it with a carbonated drink; just fill the "headspace" with a pressurized inert gas (nitrogen). This is done both to increase the stability of the container (usually more important for PET-bottles than for cans) and to extend the shelf-life of the product itself.
posted by effbot at 6:21 PM on August 29

(and in case anyone's curious, the pressurization is done by injecting a tiny amount of liquid nitrogen into the container during the filling process, using fancy cryogenic equipment.)
posted by effbot at 6:32 PM on August 29

I used to drink Slimfast from the can and noticed this whole issue as well, and I think the carbonation people are onto something. When I open a can of V8 (which I do fairly often) there is a distinct pop and release of pressurized...something. And now that I think about it, that sound and sensation is distinctly absent when opening a Slimfast. Other non carbonated beverages that come in cans, like Goya brand juices and the like, also have that signature pressure release. The only question then is, why doesn't Slimfast do the pressurization thing?
posted by Mizu at 7:14 PM on August 29

effbot: would that not cause some of the gas to carbonate the beverage inside? (co2, nitrogen, whatever....).
posted by TravellingDen at 7:26 PM on August 29

i second the whole "it's heavier and thus there's more in it" thing. seriously - it's a diet drink. i for one always feel like there's so much left in the bottom once i've gotten every last drop out of there. it's a gimmick.
posted by timory at 7:27 PM on August 29

Nitrogen doesn't dissolve in the liquid (at least not at the pressures used for this purpose), so pretty much all of it disappears as soon as you open the bottle/can - and since air is 80% nitrogen, and we're talking small volumes of gas, you won't notice it anyway.

Carbonated liquids use much higher pressures, since you want the gas to stay in the liquid in that case.
posted by effbot at 8:04 PM on August 29

These people might know.

To the OP's credit, he did try writing. I'm kinda surprised no one wrote back yet, considering they must get so little correspondence, they would've jumped all over it. They do have a phone number that can be called on Monday... Any volunteers?

Wikipedia doesn't answer the query directly. They do mention the disparity between aluminum and fountain drinks, which they speculate is the oils in the lining of cans.

While Googling, I found an Amazon customer review for a protein shake, and they cite that steel cans allow people to keep them in gym bags and such without risking damage. But I guess that's only a side benefit, since people surely would be just as likely to carry a soft drink or energy drink.

Looking at the ingredients for Slim-Fast, the ingredients don't seem to be that much different from soft drinks, other than that it's mostly milk. Are there other milk-based drinks found in aluminum cans?

And I doubt it's the psychological thing about the heft, or else everyone would do it if they thought it was worth the extra cost.
posted by TheSecretDecoderRing at 9:19 PM on August 29

A similar question that might shed light on the issue is why do canned vegetables not come in aluminum cans. The answer to this question might shed some light on the OP's.
posted by mrmojoflying at 9:45 PM on August 29

A similar question that might shed light on the issue is why do canned vegetables not come in aluminum cans. The answer to this question might shed some light on the OP's.

Aluminium cans are too fragile to use in the manufacturing process - filling a can with liquid is one thing, but vegetables are heavier, and the whole thing might need to be sterilized after you've filled and closed the container. And vegetables aren't pressurized, either.

(as an aside, some companies are switching to carton containers to save weight and increase storage density.)

I have no idea what slim-fast contains, but it could be that the product is more "liquid food" than beverage from a production perspective, or simply that the production volume isn't large enough for them to invest in a cryogenic high-performance filling production line. Or maybe they just got a good deal from the can supplier.
posted by effbot at 10:35 PM on August 29

I'd wonder if it had to do with preserving the milk, and possibly sterilizing it? Canned soup is cooked in the can after it's been sealed. Tin cans can hold up a long time, preserving the food.
posted by lysdexic at 10:48 PM on August 29

> As of 2007, nearly 70% of beverage cans were made of aluminium in Europe, with an average overall recycling rate of 62% (and above 90% in Norway and Sweden).

Somebody should fix Wikipedia then. The point remains that steel IS commonly used for beverage cans, so there might be no real mystery to investigate here.

> Or maybe they just got a good deal from the can supplier.
This.
posted by nowonmai at 11:22 PM on August 29

Aluminium contaminates milk much more readily than water I believe, so even with the coatings inside the can, trace amounts of aluminium will be found in the drink.

How much of a poison trace aluminium is is highly debatable, but that may be a reason to use steel.
posted by ArkhanJG at 3:38 AM on August 30

Living in Europe I haven't seen a steel drinks can for 15 years. I suspect its the sterilisation factor - I'd bet the product gets heat treated.
posted by A189Nut at 7:58 AM on August 30

I think Lysdexic is on the right track. This page has a similar question and a similar attempt at answer.

Quoting the good bit:

"While I wasn't able to find any official statement as to exactly why Slim Fast comes in thick steel cans, I think it's safe to surmise that it is a question of avoiding contamination of the skim-milk based product inside. Other milk products (sweetened condensed milk, for example) comes in sealed and treated steel cans, so it makes sense that Slim Fast, which can be stored for relatively long periods of time, should be packaged in a similar way."

An another note, I remember in the late 1980s that Vess brand sodas came in steel cans, so steel cans aren't just a non-carbonated phenomenon.
posted by Anephim at 12:01 PM on August 30