Ow, my head

April 6, 2011 10:52 PM

Are diet shakes packaged in cans made of significantly heavier-gauge metal than carbonated beverages? If so, why?

I was just examining a can of the "Equate" Walmart generic brand diet shake that is the equivalent of Slim·Fast, purchased from a U.S. store. It appears to me that the can is made of much thicker, heavier metal than the average 12 ounce carbonated beverage cans that I see on grocery shelves here. For example, if I were to try to crush this empty can on my forehead (as I do after finishing every can of a carbonated beverage that I drink, followed by a thunderous belch; in fact, this is required by law in the state that I live in) I think that I would cause myself a significant head injury without actually collapsing the can at all.

I peeled off the printed plastic film wrapper from the can and underneath I discovered what appears to be a machine-welded vertical seam along the side (running parallel to the axis of the cylinder.) That's totally a guess, though, as I don't know anything about welding or manufacturing things out of metal.

I also notice that both the top and bottom circular ends of the can have folded seams, whereas carbonated beverage cans only have a seam at the top and the bottom appears to be continuously molded with the sides of the can.

I seem to recall that the cans of Slim·Fast and other diet shakes I have seen in the past, even the ones that hospitals give to people who aren't doing well with solid food, appeared to be of similar construction.

So my question is: why does the construction of these diet shake cans seem to differ so much from the construction of carbonated beverage cans?

My wild guess would be that it would have something to do with a chemical reaction between the shake's ingredients and the metal or construction of other beverage cans that requires a special design. But even with that premise it seems much heavier-duty than would be necessary or economical so I'm not sure whether that's a viable guess. Or maybe it's an enormous practical joke being played on fat people who like to crush cans against their foreheads.

I would be most interested in answers that can provide at least one or two truthy-looking citations related somehow to the hypothesis of the answer. Or if there's solid manufacturing or engineering experience (or other relevant experience) behind your answer it would be cool if you could drop some really specific truthy-sounding details related to your field so that I can sound really smart when I tell stories about this at cocktail parties. (On the other hand... maybe I should go to more interesting cocktail parties than ones where anecdotes involving how beverage cans are manufactured are a hit...)

posted by XMLicious to technology (17 answers total)

My understanding has always been the opposite of yours: the carbonation in soda cans provides outward pressure that helps the can retain its shape and integrity in transit and handling, so they can get away with thinner walls.

Uncarbonated shakes don't get that bonus, so the can needs to provide all the strength from its materials. Hence, thicker materials are required.
posted by rokusan at 11:21 PM on April 6, 2011 [1 favorite]

No citations, but my guess would be that carbonated beverages (soft drinks, beer, etc.) are under pressure from the carbonation, so a much thinner gauge metal can be used for cans. The internal pressure provides some structural integrity. It's easy to crush an empty carbonated beverage can, but not so easy to crush an unopened can. Note that other non-carbonated items (soup, canned vegetables) are also packaged in heavier cans.
posted by zombiedance at 11:22 PM on April 6, 2011 [1 favorite]

You can read more about the development of cans in The Evolution of Useful Things by Henry Petroski. Amazon link

Pretty much the coolest industrial design book ever. The things we tend to take for granted are so utterly fascinating.
posted by charmcityblues at 11:32 PM on April 6, 2011 [10 favorites]

I don't think carbonation is a factor here: Hawaiian Punch and various fruit nectars (Kern's, for instance) are non-carbonated and use the typical skull-crusher aluminum can the OP is talking about.
posted by holterbarbour at 11:49 PM on April 6, 2011

Thanks for the recommendation charmcityblues! On my list.

You guys have inspired me to remove the bottom of the can with my can-opener, one of the ones that cuts below the lip and under the seam. Nothing terribly remarkable inside but I did note that the sides of this particular shake can are perfectly smooth.

In contrast, picking up a Campbell's soup can, its sides are ribbed. For our soup-eating pleasure, undoubtedly, but that would seem like even a further strengthening design element beyond the thicker gauge metal.

A thought just occurred to me: the strength of the can isn't just for containing the liquid inside but is probably even more significant to how many cans can be stacked on top of each other and what weight from above can be borne by the very bottom can. So could this also have to do with the shipping methods used? Could there be some reason that many more cases or pallets of diet shakes are stacked atop one another in a warehouse or on a ship or truck and carbonated beverages are stacked lower or differently during storage or shipping?
posted by XMLicious at 11:54 PM on April 6, 2011

V8 is non-carbonated, but comes in thin cans. When you open the can, you definitely get that pressure-release sound and minor splashing. Not so for diet shakes or juices in heavy cans. So, some kind of non-carbonated pressurization for V8 and nectars? The plot thickens.
posted by charmcityblues at 12:05 AM on April 7, 2011

I've wondered this too and always assumed it may have something to do with these drinks tending to have dairy products inside.

As said above, it has nothing to do with carbonation. During emergencies beer and soda companies will produce cans of drinking water to distribute in affected areas.
posted by birdherder at 12:13 AM on April 7, 2011

Previously. I've always wondered the same thing, and thought it was just heavier to make it seem like there is more in the can for people trying to drink them as a meal replacement. It sounds like the slim fast cans might be made out of steel not aluminum, and this is necessary because of the dairy/protein in the contents? I guess it makes sense, packaging-wise, that a can of slim-fast would be more similar in packaging to a steel can of evaporated or condensed milk than a can of soda or juice.
posted by belau at 1:07 AM on April 7, 2011 [1 favorite]

I buy Kitten Milk Replacer in aluminum cans so there are at least some dairy products that come in those type of cans.
posted by Melsky at 1:41 AM on April 7, 2011

I am fairly certain the cans are coated on the inside, so it doesn't matter what the metal is versus what the food is.

I always assumed belau's explanation was the one. As price goes, the difference isn't all that great between a heavier steel can versus a lighter aluminum one, so why not choose the heavier one?

For all we know, they are in steel cans simply because the first people to make a Slim-Fast-type beverage only had access to a steel-can-making machine and it just became the form that shakes in a can were expected to be in.
posted by gjc at 4:19 AM on April 7, 2011

why not choose the heavier one?

Shipping costs. Have you seen the price of fuel these days?
posted by the cuban at 6:15 AM on April 7, 2011

I think there are several factors here. One is probably pressure and the other is certainly acidity. Diet shakes and other milk products are very low acid foods, so to prevent spoilage you would need a thicker can that is resistant to pinholes and cracking that would allow bacteria to enter and throw a party. Bacterial contamination is not as big a problem with high sugar, highly acidic foods like soda and juice.

This doesn't explain the thick can on higly acidic canned tomatoes though.
posted by kuujjuarapik at 6:59 AM on April 7, 2011

I have always assumed this was a marketing choice. Slim Fast is sold as a meal replacement drink. Consumers likely feel that a meal replacement drink sold in a heavier can is more filling than one sold in a light can.
posted by DarlingBri at 7:35 AM on April 7, 2011 [2 favorites]

At Safeway, there are some diet shakes / meal replacement drinks that are sold in cardboard cans, sort of like a big juice box. *shrug* I dunno what to make of that.
posted by xedrik at 8:39 AM on April 7, 2011

Palleting is probably the answer - shakes are much denser than softdrinks, and to stack a pallet with a suitable number for shipping, they need stouter cans. It's probably cheaper to use more metal in the packaging than to ship fewer cans-per-cargo container.
posted by Slap*Happy at 8:52 AM on April 7, 2011

Perhaps they have different processing requirements. Steel cans may work better in the standard canning equipment if the product needs to be pressure cooked for sterilization.
posted by JackFlash at 9:30 AM on April 7, 2011 [2 favorites]

Thanks for the answers so far, everyone! Especially the link to the previous question, belau, I managed to miss that even though it's the only other question with the "Slim-Fast" tag.

Yeah, DarlingBri, my instinct is also that it conveys some marketing message like "more filling" or "dieting is manly!" or "it's heavy-duty, like your exercise equipment!", it just seemed feasible that there's some food safety or manufacturing reason for it, so I was fishing for cites.

Well, for the sake of SCIENCE!, the Wikipedia article on beverage cans names 3104-H19 as one aluminum alloy that cans are made out of and this page lists 316 stainless as a common alloy of steel used for food containers. Mashing it up, the "Tensile Strength, Ultimate" listed for the aluminum is 290 MPa while for the steel I think it's 579 or 558 MPa. So on some measure it's approximately twice as strong (at the same gauge, I assume there's a testing standard?) though I don't know how that plays into the various strength hypotheses.

Not sure how to investigate the hypotheses on acidity / chemical reactivity or compatibility with processing equipment via Google quickly, so I will leave that for another day...
posted by XMLicious at 10:28 PM on April 7, 2011