I told a cat food company how much they’d save by using taller cans (2020) | Hacker News Reader

I told a cat food company how much they’d save by using taller cans (2020)

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246 pointsTomte158 comments

For those interested in the original source, one of the replies [0] links to [1] which says that you can find the letter in Applied Mathematics by Farlow & Hagggard (Pub. Random House, 1988) p613.

> "There is a nice letter from the Carnation canning company which is reproduced in Applied Mathematics by Farlow & Hagggard (Pub. Random House, 1988) p613 on why cans do not adopt this optimal shape."

0: https://twitter.com/theohonohan/status/1235646988357701632

1: https://plus.maths.org/content/comment/8352#comment-8352

Does that mean the twitter account is either Farlow, Haggard, or just somebody posting things as their own?

A cursory scan of their twitter account shows that it's the latter.

Also they reposted the story wrong, assuming cans were short.

The tweet-author being the original letter-recipient is not necessarily inconsistent with them also having forgotten exactly what they suggested 35 years ago and just substituting in a general sense of what current cat food cans are like. Particularly since they'd be, you know, 84.

I feel kind of stupid reading this since I sometimes (often?) forget the exact details of things I've written just 3.5 days ago (!).

What makes you say that? I skimmed through a couple pages of tweets and it seems consistent with the twitter account belonging to Farlow.

Somewhat surprising for an 84-year-old math professor to have an active twitter account, but not out of the question.

Strong evidence that the account is indeed Farlow: the profile links to a pinterest board [1] which is listed by the NCTM [2] as being run by Farlow.

[1] pinterest.com/mathematicsprof

[2] https://www.nctm.org/tmf/library/view/75908.html

It would be a strong evidence if the linking were the opposite way.

If I link to the potus piterest page from my twitter page, it would not mean anything.

> if the linking were the opposite way.

the linking goes both ways: the pinterest page also points to the @mathematicsprof twitter handle.

Thank you, I really hate when people post an image of text and consider themselves smart for shortcutting normal posting.

A while ago, I noticed that the bread I eat sometimes had the twist tie twisted clockwise and sometimes counter-clockwise (annoying since that is the direction it should untie). I called the company to ask why and they left a message with an explanation. It wasn't a great explanation, but I was impressed they responded. They said that the breads comes off the conveyor belt and are routed two ways and the twisters are different.

I grew up in a house with a left-handed dad and sister. Half the time, the twistie was 'the wrong way' and in opening it, I'd instead twist it into a hopeless knot.

Was a bachelor for 3 years on my own, and counted my blessings every time I opened a loaf of bread. Then got married. To a left-handed woman.

I wouldn't have expected that the CW to tighten things convention was linked to right/lefthandedness. Especially since many people seem to not have a notion about the convention.

But maybe that's my right privilege talking.

I think it's more natural to twist things thumb-over-index. index-over-thumb is a slightly awkward movement, at least for me. this corresponds with the right-hand rule (relative to your hand).

You get more power pushing with your thumb than pulling with it. My thumb is stronger over one way over the other.

sorry, confused myself with that bit about the "up" direction of the bag. I think we agree.

Righty tighty, lefty loosey, right? But I don't think there is a convention when it comes to twist ties, because a twist tie isn't something that gets tighter or looser. It's more closely related to spinning.

I'd bet lefties spin tops counterclockwise, too, by and large. Seems to me it comes down to external rotation of the wrist being easier than internal.

When I twist something I prefer to twist the top of my hands out, so I would twist something different if I was holding the tie with my left or right hand. So I absolutely believe that the handedness affects this because it will change which hand holds the bread and which holds the twist tie. If I hold the bread in the left (twist with my right) I would twist it clockwise (righty tighty) and if I held the bread in my right I would use my left and twist counter-clockwise.

> Righty tighty, lefty loosey, right?

This phrase always irked me, because when you're rotating something, it's not moving either left or right. The top of it moves right, the bottom moves left. Is it tightening or loosening?

Further, the only time a phrase might be needed to work out which way to tighten something is when it's unusually-positioned, for example upside down or facing away from you, and in those cases "righty tighty, lefty loosey" gives exactly the wrong answer (to the extent that it gives an answer at all, since "clockwise" and "right" are not the same thing).

I prefer the phrase "clockwise moves the thing you're turning away from you, anti-clockwise moves it towards you", which I'm hoping will catch on.

I've adopted the right-hand rule: The screw goes the direction my thumb points when my right hand closes. And if it's something left-handed like a bike pedal, it's easy to just use the other hand.

I feel like this is the sort of thing that actually makes less sense when you develop explicit reasoning skills. as a child, "righty tighty, lefty loosey" made perfect sense. it never occurred to me that right/left could be relative to the bottom (from my perspective) of a jar lid. only when I started learning about math and coordinate systems did I think "right/left relative to what?".

I prefer "clockwise lockwise".

The phrase is talking about the top surface of the circle as the circle is facing you, since that’s normally where your vantage point is when you’re turning something with your hand. You have to think things through more carefully if the circle is oriented differently (imagine reaching through a broken window to turn a doorknob).

> Righty tighty, lefty loosey

I remember an old mechanic sarcastically saying this when I was a kid and as as he worked on an old car that had wheel nuts that did up the other way on one side of the car.

It really pissed him off.

A quick search seems to show that this was a thing. https://www.quora.com/Why-did-the-old-Chrysler-cars-have-lug...

I read the first answer there, but it didn't answer the related question: why don't all cars have that weird setup now? Is there a modern design feature that we have nowadays that allows for normal threading on the left-side wheels that keeps them from coming loose?

I think it's:

> Improvements in metallurgy, changes in brake design, first to finned drums and then to disks, and changes in wheel nut architecture, from flat washer to conical design have effectively reduced the problem.

Think of the vantage point of observer standing (& his land under his feet also rotating with circle causing him to always rotate along the rotation.) at the center of that circle. ACW will always be right moving to him, CW will be left.

The other is, follow the fingers not thumb.

I'd guess it is related to the conventional way steering wheels work--turn clockwise to steer the vehicle right, counterclockwise to steer it left. Hence, clockwise gets associated with right and counterclockwise with left.

I have no idea why steering wheels work that way. If I had to guess it would because most steering wheels are below eye level so it makes sense that you move the top of the wheel in the direction you want to go.

Note that if you are holding the top half of a steering wheel that follows this convention, then when you turn the vehicle the centriwhatever force on you will tend to oppose the force you are using to turn the wheel. If the steering while used the opposite convention, that force would reinforce your force. That positive feedback would make it a lot easier to lose control during the turn.

Without power steering, holding the steering wheel at the top gives you more leverage than holding it at the bottom. When holding the wheel at the top, turning right is a matter of moving your hands to the right.

ITT people who have never used a wrench.

> This phrase always irked me, because when you're rotating something, it's not moving either left or right. The top of it moves right, the bottom moves left. Is it tightening or loosening?

And the answer is "You look at the top, of course, why would it mean the bottom?"

As a lefty I visualized myself spinning a top - it's clockwise. That's because I'd use my right hand to spin a top. Do righties not use their left hand to spin a top?

I'm right handed yet I generally use my left hand for twist ties. I twist them counter-clockwise too. I never put any thought into it beyond wanting bread.

As the only left handed member in my family, I'm now curious if I ever did that to my family. Though for tasks of that nature I may actually use either hand, or maybe I just started using the right hand because I was the weirdo (asking my mother she said she never noticed but assumed I probably just adapted and used my right hand).

As a bachelor I virtually make all my own bread so I don't really notice, but I think I do take time to figure out which way to twist before opening so maybe that is a thing.

This is just to say, the things you never think about, and I enjoyed the irony of your situation from the reverse side.

> As a bachelor I virtually make all my own bread

I so wish that the status of bachelor automatically bestowed the gift of being a baker. Sadly, in my case, it has not done so. I've tried to make all kinds of breads, from flatbreads to sourdoughs to leavened and unleavened to soda breads - all sorts. I would wish consumption of my output on only my worst enemies.

Happily, though, I can buy packets of bread mix in the supermarket and put them in a bread-making machine.

You should check out The Tassajara Bread Book by Edward Espe Brown; it's a masterwork of clear technical writing. The first basic recipe is expanded over 20+ pages, explaining not only what to do but _why_.

OK, I will do that, thank you. I'm a fan of Cooking for Engineers, and particularly like the schematics. Scroll to the bottom of this recipe to see what I mean:

http://www.cookingforengineers.com/recipe/36/Meat-Lasagna

For an easy and delicious recipe, try Andy Jones' "quarantine bread" [1]. I was rarely baking bread before, but this recipe changed that completely. As he mentions, it is really really hard to mess up. I once put it in the oven without folding. Thought that this was irrecoverable. It wasn't. Turned out great.

[1] https://andyljones.com/posts/bread.html

I honestly only did it because I was cheap and I wanted to remake a sandwich I had consumed before. I started with a simple foccacia recipe and went from there. But I started baking with my mother years earlier so I had some experience.

I now for better or worse have the Toll House cookie recipe memorized, but I'm terrible at making baked goods look appealing.

Get some spring clips: https://www.amazon.com/dp/B07VJJWSL9/ref=cm_sw_r_cp_api_glt_...

Nice find. Ordering now.

I just fold the end of the bag over and use the weight of the bread to weigh it down.

That way I also have an excuse to not eat the last slice.

Come to think of it, I haven't kept bread around for at least a year.

Just use a clothes pin? It’s faster too.

While this thing is ancient (it's dated 1987 after all), it's funny that the Twitter caption gets it so wrong.

The Twitter caption is supposedly about making short cans taller, while the letter is clearly a response to making tall cans shorter (points 2, 4, 5).

If you're going to make a repost at least get it right ;)

Ancient? I resemble that remark :-)

This is funny, but did you mean ’resent’?

It's a common joke to say that you resemble a remark when it applies to you. Dano is joking that they too are ancient like 1987 (you know, from the prior millennium).

another example of "why don't you just"- the tendancy of technical people to tell other people technical people how to do their job better, without the necessary context to understand why it is a way (chesterton's fence).

Agree absolutely. It also reminds me of, “For every complex problem there is an answer that is clear, simple and wrong.”

I don’t know how people have the ego to think they’re going to study a problem for an hour or two and discover solutions that have eluded competent people that have spent their careers studying the problem.

It’s much more complicated than that. Sometimes the people who start from scratch actually lead to real innovation while the scholars are stuck in their old world view. There is room for both types of exploration.

I get your point. But that innovation comes from experts too, not someone who watched 10 YouTube videos on the subject.

I would say most novices soon find out why things are done the way they are done. True innovation is really exceptional.

I've run into all sorts of things in my career where competent people completely ignored parts of the problem. Someone, qualified or not, spending two hours studying the problems would apparently have been the first two hours spent; and to good use.

Many times, I've stumbled across reports from other fields about solving problems in ways well known for their field, but unknown in mine that would apply well for some problems in my field. A (kindly worded) suggestion and reference from someone who thought to be helpful would be useful.

Of course, some fences are Chesterton's fences, and some are just randomly placed fences in weird spots.

Chesterson's Fence is the act of DECIDING without knowing. There's nothing wrong with SUGGESTING without knowing. In fact, that's a very desirable thing. Different disciplines bumping into each other and making such suggestions is how great ideas and great solutions are hatched.

I think there is another one to add to the list, which is assuming something is wrong without knowing enough about the problem to know why something is the way it is right now.

E.g. Instead of telling a cat food company how much they would save with a different size, you could ask a company why they don't optimise for the lowest surface area, or if they have considered it. The first assumes you are right and they are wrong from the get go, while they are the domain experts.

Really interesting dialogue though!

Assuming wouldn't be a problem either. Since the person assuming is not in a position to decide policy, no harm can come of it, and possibly a benefit could result if he happens to be right.

"Ask vs Guess" is one difference between people.

Roughly, "it should always be okay to ask, since they can always just say no" vs "saying no is a bit awkward, so only ask for things if the answer is going to be yes".

In terms of the above:

Sure, the person doesn't have to apply the suggestions. But the only reason you'd make a suggestion is if you think something's wrong or could be improved. And suggesting something is wrong if it isn't is awkward. etc.

I just think it's just good practice to remain humble, and consider that the people who own a giant tinned cat food packaging line just might know more about tinning cat food than you do, with your degree in maths, and frame the question as 'why do you not optimise to the minimum packing material?' rather than 'you should optimise to the minimum packing material'.

I personally find that approaching problems with an attitude of "Why do you do it like that instead of like this?", or even "have you considered this?", usually provides more insight and a more collaborative discussion than "You should do it like this".

I ask that all the time, but start with "Pardon my ignorance" or "I know you must have good reason, but..."

I did that just yesterday with a comment here on HN: https://news.ycombinator.com/item?id=26044548

That's also a useful managment tool. I often ask "Uninhibited by any actual knowledge, I would think X is the easier solution, what's the real story?" A competent team will either explain why things are the way they are or give you an improved version of X that may be faster than what they had you if you're willing to accept the associated limitations. Often that dialogue on limitations is valuable because the client facing people may know some things about what limitations can be accepted without client impact and are thus good choices.

Your post is an example of attributing to technical people the bad habits of all people. Much like, "engineers are bad at business" -- people in general are bad at business.

Every person out there has a brilliant idea that just needs to be implemented (by someone else), fitting nicely into the "why don't they just".

Engineers are conspicuously good at something and then it's fun to make fun of them, but I don't think their behavior in this regard is any different than anyone else, except that they may more frequently give thought to solving something.

It's interesting to see this exchange, though, because it's high-trust: I would bet the professor's initial letter was courteously written, and asked if there were other factors besides purely surface area to volume. The responder wrote a clear technical letter without any marketing flim-flam. We are in a golden age of communication in some sense, with blogs and technical online communities. But I could hardly imagine getting a letter from a corporation of this quality.

> the tendancy of technical people to tell other people technical people how to do their job better

"why don't you just" is a question, and if they had not asked said question they (as well as the readers of their book) would not know the (right) answer to it.

It’s clearly phrased with the implication that the person has never thought of doing it the way the speaker is suggesting.

Why don't the IDIOTS at Heinz just make goddamn spherical ketchup?! Everyone knows that a perfectly spherical ball would reduce the amount of packing material per ml of ketchup yet they are just closing their ears and not listening to the maths.

And don't get me started on the cereal box people... THEY SHOULD BE CUBES.

And I'm looking at you water bottles - if you were all cubes too don't you realise how you could nest to avoid air during shipping? They could have cut outs in the bases for lids... Idiots everywhere!

I'm going back to my car. It runs on petrol because the idiots in engineering haven't worked out it could just run on hydrogen yet.

(All the above have reasons for being the way they are, and I think it's usually a good idea to understand why something is the way it is before you try to change it)

I can't see this post as anything but a strawman. Yeah, let's presume that they insulted them and even slapped them before they made that question, why not.

It's implied.

What if someone that had no idea about programming came over and told you that you could program faster if you used a for loop, without ever reading your code? They probably think I suck at programming, or think a bit too much of themselves.

This is a mathematician telling canned packaging experts that they could save money by considering the size of the can.

We are talking about asking though. Like "why don't you just use a for loop? Wouldn't that be faster?" or "I think that a for loop would be faster, why are you not using it?", both seem absolutely fine to me.

I think we are talking about telling rather than asking though. “I told the cat food company they could save money.

I am only defending the sentences starting with "why don't you just" and ending with a "?". I am not defending nor support aggressive ones like the one that you mentioned.

It's strange. Almost everyone I know in real life, when told "Why don't you just do X instead of Y" treats it enthusiastically as a chance to share some nuance about their field.

Two instances recently come to mind, my asking my father (an orthopaedic trauma surgeon) why we don't just make hips (in total hip replacement) out of dead people's bone instead of out of whatever material they do now, and my father's asking me something about why blue LEDs are supposedly so hard (why don't you just wrap them in blue film).

On the Internet, everyone is always like "you guys always think you can do our job better!". In real life, everyone is always like "hmm, that's interesting. Let me explain why". But perhaps it's just everyone I know.

I saw this the other day too in another HN comment⁰ where people assume that "Why don't you just" and questions like that are demeaning.

0: https://news.ycombinator.com/item?id=25826835

I presume this has to do with how you frame the question and the recipient perceives your intent.

I'm sure I agree, but surely there is something to how so many commentators here clearly immediately assume that the Prof's question must have been framed so that the best interpretation is condescending.

Absolutely - in fact in 2021 you might even be accused of mansplaining, when actually the purpose of asking these questions is to genuinely learn more about why the world works the way it does! (And of course there are the occasional examples of genuine insights gained from having a fresh perspective - I remember reading about Alan Sugar discovering that he could make satellite dishes for a tenth of the cost by contracting the manufacture out to a bin lid factory)

I think we've hit the result of heavy social pendulum swings. There are enough people who actually do mansplain in the very negative way that the assumption has become that any attempt to explain something in that manner is assumed to be mansplaining unless proven otherwise.

It's disappointing, because it shuts down any form of reasonable discussion, and causes people to automatically assume the worst intentions without applying the principle of charity. But on the other hand, mansplaining is actually a real, pervasive problem, so it's understandable that people can become viscerally negative toward anyone who starts explaining something without first verbally demonstrating humility.

I think this is fair. More broadly I'd add that we've become quick to accuse the speaker of bad intent and too rarely consider if the listener could have been more charitable. And god help you if there's someone in the room intent of hearing you uncharitably, regardless of the feelings of the person you're actually addressing. The most uncharitable interpretation will usually prevail.

It's all about the context.

When you ask your father why something is done a certain way, you're seeking information. You're not questioning the competence of his field or implying that you have seen an obvious solution that his entire field has simply missed.

However, when engineers say "This change will require 4-6 weeks" and their boss says "Can't you just add a form field and run a database migration and ship it tonight?", the boss is casting doubt on the team's assessment of the situation and their competency in executing.

The demeaning nature varies with intent. If someone is asking a simple question ("Why can't we just ship it tonight? Help me understand") it's nowhere near as bad as a boss waiving away objections with an over-simplified order ("Just change the code and ship it tonight!")

I don't think anyone would object that that kind of negative reaction to a repeat offender (the hypothetical manager) who has demonstrated through repeat behavior that they have little respect for their employees' expertise.

What is a bit more pervasive, though, is a growing belief that any question of the form "why can't you just...?" is inherently condescending and rude.

Yes, I agree that a "help me understand"-style question is the ideal way to ask, but I think people have definitely become more (IMO unreasonably) sensitive against the "why can't you just...?" form, when often it's asked innocently and without a trace of disrespect.

Something I always try to remind myself: I can't control other people's behavior, but I can control how I react to it. We should try to gently correct truly bad behavior when it is safe and constructive to do so, but it generally does us no good to get all worked up about it in the first place, especially if it's something as benign as a poorly-worded question. And being impatient with these sorts of things can be to our detriment; sometimes a fresh, layman's perspective can provide an insight we hadn't considered.

I think a big part of it comes from the inclusion of the J word. If you just remove it from the question, it comes off as significantly less arrogant and will tend to ruffle fewer feathers. Unfortunately, it is deeply embedded in many of our vocabularies. I'm actively trying to scrub it from mine (except when something really is that simple, or to demonstrate the effect, like in this post).

Okay... why _don't_ they just make hips out of bone, and why _can't_ you just wrap LEDs in blue film?

modern bone replacement uses cadaver bones, so the answer is "they do". As for LEDs, if you're using a color filter, that's filtering out the vast majority of photons so it's not bright or efficient.

Isn't it with LEDs also that getting a spectrum that has blue you could filter is about as hard as getting just blue? (e.g. white LEDs are some form of blue/UV with an extra fluorescent layer, and from a (simple) red LED you can't get blue by filtering?)

Sometimes it’s important to answer those questions: it spreads knowledge and generates trust in the expertise of the person being asked. Sometimes the suggestion might actually be a good one, too.

The most shocking part of this to me is that someone had the time and knowledge to reply to this. Is this common in any companies anywhere still? In my experience customer support usually knows nothing about the product, they are there to read off a script and maybe authorize a repair/replacement. That you'd get a reply from someone who understands thermal requirements for sterilisation sounds almost surreal.

Author sent the suggestion to the marketing, marketing forwarded it to engineers and the engineers took that personally. It was sort of like Torvalds C++ response.

I had to Google, and I think this is what is meant with "Torvald's C++ response": http://harmful.cat-v.org/software/c++/linus

You might be able to get a response like this today if you mention the brand on Twitter - that's usually a more marketing-oriented support channel.

Yes, you could tell this letter was very dated and not just from the type. I don't think you'd get a response like this at all these days (if at all).

Maybe if the brand hooked into it as a marketing effort they might publish a response all over their socials, but you'd certainly not a private reply.

My UPS will occasionally go on battery because the incoming line voltage crosses it's "too-high" threshold (127V). I sent the power company a dump of the logs and requested they adjust the tap on my house's transformer.

No response, and I'm pretty sure I'm on their "this guy is a crank" list now.

If you look at the end, you’ll see the letter was signed by an “Assistant Product Manager.” In tech we might call that position “Junior Product Owner” or “Technical Product Manager.” It’s exactly the position I’d expect to either have the answers, or have good enough relations with engineering to get the answers.

My dad had various Plant Manager and Production Superintendent roles at Goodyear for many years. He could tell you exactly how each machine the factory operated, and why, and what the functional tradeoffs were of different designs. He had a Master’s in engineering, which again is a common path to this sort of role even in tech — join as a capable engineer, learn the product and industry, and somewhere along the way learn that you have either talent or interest in management or communication.

If you ask support questions of AWS, you often get connected directly to the engineers responsible for the product, who are able to hunt down the cause of quirks for you by direct reference to their code.

What impresses me the most about this is the quality of triage required to pass just the questions that really need it on to the engineers to avoid oversaturating their bandwidth. I got connected to them almost immediately.

Well yes, maybe I worded my question incorrectly. I work at a games studio and if we need to, we can get direct access to the engineers working directly on the Xbox firmware and ask them questions. It's possible.

But I'm also 100% certain that if someone sent a random letter to Microsoft offering advice on the design of their Xbox console, it wouldn't even make it to their engineers, much less actually get a response from anyone within the department.

Most of the time consumer dont interact with the companies that are doing the "Real" production. Mostly stores, distributor, wholesaler, or White Label companies. Normally these entities are created only for marketing and sales. So most of the time they dont give a damn.

Real Product companies tends to take these things seriously. Or at least try to explain these sort of things.

But that is only limited to small -medium , family ran or private companies. Once you get into large public companies there are things that can not be said without first clearing with legal.

LOL I can imagine how this went down when this letter came in at this cat food factory.

Marketing: Hey you engineering nerds. We just got this letter from an actual Professor, saying we can save money changing the designs you made us use for the cans! Fix your mistakes or prove why the way you made it is better!

Engineers: Hold my beer.

Highly recommended related YT video:

The Engineering Guy: The Ingenious Design of the Aluminum Beverage Can

https://www.youtube.com/watch?v=hUhisi2FBuw

I know for a fact that I've watched this before but still I just had to rewatch it.

This letter argue that a tall-thin can is better, but most of the cat food cans in market are short and wide. Only the first and third point argue for short-wide cans (while promoting tall-thin cans as well).

https://www.google.com/search?q=cat+food+can

There are obviously more concerns that are relevant. Most of these containers contain single servings or maybe a few. Open cans of cat food smell. Thin cans of single servings would be narrow, getting the food out would be a pain.

Exactly! Now explain 'tomato paste'. Comes in tall thin cans like miniature tomato-juice cans, but just 1" wide. Impossible to get all the paste out! Or even, any of it. Why? Why? Why?

I think the way to do it is to cut one end of, then the other and use it to push the paste out through the can. Doing that I've never had a problem.

Thats also the trick for sliding out the cranberry jelly-loaf things.

Ocean Spray realized this and made the bottom of the can un-openable. So now you either have to use a knife or squeeze the can enough to loosen the cranberry jelly loaf. I've found the same trick works on refried beans, but it's not as amusing. lol.

They make lovely squeezable tubes. I would suggest giving them a try! They are much better.

I guess I'm reluctant to eat acidic stuff out of plastic. But I suppose tin isn't much better.

I just reduce my own tomatoes if I need paste.

Oh! The tubes from Cento, which is a particular good brand, are metal. I understand the acidic substance from plastic concern. Though reducing your own is a good idea as well. If you grow the tomatoes they will be significantly better.

They have that at WalMart! Sounds good, will give it a try. The case-of-12 description is a little concerning. Its apparently 'Adult Unisex'. Not sure what they think I'm going to do with the paste...

All cans are lined with plastic, also a reason why you shouldn't use metal utensils to scrape all the contents out of the can

Enamel, surely?

They are all metal tubes, and I guess the lining, which is plastic, is exactly the same as in the cans.

Possibly ironically, the plastic lining cans is usually toxic but regular tubes are made of polyethylene which is safe!

>I guess I'm reluctant to eat acidic stuff out of plastic.

It might help to realize that plastics are extremely resistant to acids. Hazardous Industrial acid products, far stronger than anything a consumer can purchase, are stored in Polypropylene barrels. Generally speaking plastics are considerably more resistant to inorganic chemicals than even specially formulated metal alloys.[1](link even lists the resistant data for tomato juice :)) Additionally, metal used for canning is usually(always?) lined with plastic[2] to keep metals from leaching. Ironically canned foods with bpa liners are one of the biggest vectors of BPA intake we know of.[3]

[1]https://www.usplastic.com/catalog/files/charts/LG%20CC.pdf [2]https://www.ewg.org/research/bpa-canned-food [3]https://www.sciencedirect.com/science/article/abs/pii/S00139...

I always rinse out the remaining with a little bit of water. The water will boil out anyway when I cook.

Take off both ends. Slides right out.

At least here (Finland) the “standard” cat food can is taller than it is wide [1]. Smaller, shorter containers are mostly used by the more “premium” brands.

[1] https://www.puprise.com/whiskas-tuna-in-jelly-wet-cat-food-c...

Interesting! While I realize I have seen those style cans, nearly all cat food cans in the US that I've seen are shorter than they are wide. There seem to be two standard sizes, both with the same height (I think; they might be slightly different, but close) but different diameters.

"Most cans" you see there are the small ones. But as the quantity grows, it is the height of the can that grows, and not the diameter. https://www.google.com/search?q=large+cat+food+can

The letter is from 34 years ago. What did most cat food cans look like then?

The title doesn't mention the interesting part -- the company responds with reasons why they made their cans a certain size. Definitely worth clicking through.

I'm not sure about 1987, but today, Carnation is a lot more than "a cat food company".

It's Nestlés all the way down.

I am pretty sure this letter/meme has been around for years and this twitter account isn’t the original author, but it’s a good explanation of why cans are like they are, maybe, if anybody involved in this story exists.

This is an example of the sort of foible of which people on HN are constantly guilty.

Just because you're an expert at one thing does not make you an expert at everything.

This is true, though that said, on the flip side of things; exchanges like the one between the letter's author and the cat food company are exactly the sort of thing that helps expand one's understanding outside of their own domain of knowledge.

Be it out of hubris or genuine interest, that the author of the letter felt compelled to write to the company, they (and by extension us) received an insight into the decision making process behind one of the more mundane pieces of engineering we see on a daily basis (I certainly did)

It was a good reminder that creation of many things takes overlapping disciplines. It reminded me of a joke about a mathematician optimizing a farmer's operation. He returns after several months bursting with excitement, promises of improved profits.

"First, we assume a perfectly spherical cow..."

What is left out from the letter is that the marketing department probably have a say in the design too. Nowadays they probably have tested which geometries that sell best to different target groups.

And then we also have the user perspective. A short wide can is easier to scoop from.

Yea I was expecting an argument that their cans stand out on the shelves and lead to higher sales.

I don't want a tall cat food can. we feed the cat out of the can, it can't reach the bottom of a tall can. Also, if you don't feed out of the can, now you have to store half a can of wet food in your fridge (ew).

> we feed the cat out of the can

Don't you get problems with sharp edges that way? Also, even short cans have a geometry that I would expect to be hard to clean out completely with a cat's relatively short tongue. Also, cans are very light, doesn't the cat move the can all over the place compared to a heavier feeding dish? So many questions...

> Also, if you don't feed out of the can, now you have to store half a can of wet food in your fridge (ew).

Around here many people have reusable plastic lids to put on open cans, those work well. The bigger problem is feeding fridge-cold food to your cat, which is apparently not ideal. When I had cats we mostly fed them with individual portion-sized pouches. That generates a lot of non-recyclable waste though.

for the sharp edges, I haven't noticed a problem with that. The cat sort of eats from the middle, not the sides. We put the can in a larger plastic thing- which would normally hold a cat food bowl (IE, it's the thing that holds the cat food bowl in place) so it doesn't move around.

Over here, we simply don't put cat food into the fridge. The very concept of that is just alien to me.

We're talking about an open container of wet, meat-based food. It will be prone to spoilage. Though I guess you could argue that if you feed one half of the can now and the other half in not more than 12 hours, it will probably be fine.

Oh, that was more in relation to still closed cans.

Get a lid: https://www.amazon.com/dp/B0746MLFB7/ref=cm_sw_r_cp_api_glt_...

Poor cat. Must have hurt his tongue so many times and you won’t ever find out.

I'm curious about this (since I don't want to hurt my cat). Wouldn't he show pain or have a bleeding tongue?

This reinforces the old saying. "Don't take down the fence until you know why it was put up." I wish more computer science programs taught this as an important principle. Too many people today assume that if something is newer, it is necessarily better, and rush to rewrite or replace things that had been working well, and would continue to do so, with new and untested and unproven replacements.

Okay but what really bothers me are square powdered juice packets. This is the only way powdered juice comes in my country and we're all poor and re-fill soda bottles, so WHY the hell are they square? Powder spills everywhere. Why are they not tube shaped. And why aren't there ones for small water bottles for on the go? One of these days I will write to the companies...

This is so odd to read, as in the US there are certainly tube-shaped single serving drink mixes (indeed, I have one sitting on my desk right now). For example: https://www.powdermixdirect.com/Gatorade-Sqwincher-Single-Se...

I lived in the US for a while but was never a heavy powdered juice drinker, but I don't remember these types. I think I remember some other tube shaped ones but not these energy drink ones. Is this a new thing? I feel I would have heard about powdered Gatorade. Sounds amazing.

It's so weird here too because everyone drinks powdered juice all the time, but that's the only format it comes in, it doesn't even come in bigger quantities in cans, which I know exist. For example, one of the brands we have is tang which comes in all sorts of packaging elsewhere, but only packets here...

More scrap metal is generated as the diameter is increased.

Can anyone comment on why that is?

If you imagine cutting out rectangles from sheet metal, you can completely tile the plane. Punching out circles, you'll use a maximum of roughly 91%. So I imagine the more of your material you use for the sides, the less scraps you'll end up with. I'm sure the problem is a lot more complicated than this though, with deburring, corrugation and whatnot.

Edit: Disregard this. The other answers are better.

I guess it's because of the fat ends - if these have constant thickness, the volume will only increase as diameter changes.

My first thought was for the ends, and for a similar reason that the smaller diameter cans pack more densely.

If you're punching circles out of sheet metal, you'll get more waste with larger circles.

> If you're punching circles out of sheet metal, you'll get more waste with larger circles.

I don't think you would. The design can be scaled up or down without impacting the proportion of the area which ends up being 'useful'.

The percentage waste per circle remains the same, but the absolute amount of waste per can goes up.

One explanation could be the following based on the supposition that one starts with rectangular pieces of metal. To minimize waste for a circle one begins with a square piece and cuts out the maximum circle contained therein. The waste is (area of square) - (area of circle). If the circle was to be 4 inches in diameter (2 inch radius) cut from a 4-by-4 square the waste is 4^2 - Pi2^2 = 3.43, whereas a 2 inch diameter circle cut from a 2-by-2 square has waste of 2^2 - Pi1^2 = 0.86. The cylindrical side needed to achieve a given volume is rectangular so has no waste in either case.

From a 4-by-4 inch square you can make 4 2-by-2 inch squares, therefore the loss from 4 small squares would be 0.86x4=3.44, same as one large square.

One factor missed in other answers, mentioned in the letter, is that the ends are made from thicker stock than the cylinder, and increase in thickness as diameter increases. The scrap ratio of the ends doesn't change in area, but the volume of scrap per can does.

What's interesting is how the letter's scrap argument has aged - take a look at cans in common household sizes today. Most are only capped on one end. The cylinder and opposite end are a single deep drawn [0] unit. That can body will consume a round portion of material and definitely increases overall scrap ratio over old double-capped cans.

[0] https://en.wikipedia.org/wiki/Deep_drawing

I note that here in the UK, cans of soda tend to be deep drawn, capped at the top, and that most food/soup cans are of the traditional double capped variety. I wonder does this come down to the pressures of the contents or is there another reason involved.

I do a lot of manufacturing adjacent and overlapping work. The primary justification for cans (by a long shot) is going to be process steps and cycle time. Very roughly counting manufacturing operations, while surely overlooking tons of other handling and preparation common to either method:

A double capped can has 7 specific manufacturing tasks: 3 cutting steps (2 ends, 1 center), 1 roll forming step, 1 weld step to close the cylinder, and 2 end capping steps. Forming ribs into the cylinder and can should happen simultaneously when the cylinder is roll formed and when the ends are punched from sheet stock.

A single capped can has 4 specific manufacturing tasks: 2 cutting steps (1 blank for the can, 1 lid), 1 draw form step, and capping the end. Trimming the edges of the draw formed can should be combined with the forming operation.

Draw forming tools are expensive, the world is still full of cheap, perfectly functional, secondhand canning equipment. Either way, cans sell for cheap and at low margins. Takes a lot of volume to make ROI. Or... Aluminum! Aluminum is far more expensive than steel and is finicky to weld reliably. Draw forming soda cans eliminates any need for welding and allows manufacturing of thinner can walls, which reduces material consumption, and the bottom can be shaped to hold pressure with less material.

Thanks for sharing! I assume it's the dome shape on the bottom of a soda can that's specifically there for holding pressure in that case (a balance of accommodating the greatest strength per unit surface area measured against the cost of the forming process)

I wonder if the customer service department at a large FMCG company would be so empowered as to send such a detailed response these days. I'd expect either no response or a generic answer with goodwill a voucher.

I was impressed they'd send such a letter at all. On seeing your comment, I now notice that the letter was written in 1987.

I did something similar once, mailing v8 about how they could make their cans squatter. I even wrote a script to find the optimal shape. I think it went straight into their crank file.

Well, besides the reasons given I'd say they probably buy these cans ready made so custom cans would cost a lot more due to economies of scale.

It's also cheaper to just buy a normal bag of ground coffee and brew it in a french press/percolator/whatever than buy those coffee pods which taste more like boiled cat shit than actual coffee. Keurig would make the same letter to the same high horse professor. Are you going to say Keurig is stupid for not selling bags of coffee instead?

Doesn't matter how smart someone is, they always forget that economics doesn't give two shits about their feelings or how shiny their degrees are. Fancy little prefixes and suffixes to your name doesn't help change reality.

People buy things for a multitude of reasons. Because people are unique and allowed to do what they want for themselves, they tend to like and value things different from you. Companies capitalize on that.

Hell, want to get into some real nerdy math academics and economics? What about that Japanese chalk so many of them love to use? Something so exquisite and special to the professors of the world for black board lectures. They went out of business. Why couldn't your fancy letters and diplomas save that important product? Where are the equations for that one?

No, the response had good reasons, not like your "lol yeah but people be crazy" stuff.

Current cans of cat food are setup as either a single meal or enough for 2 meals a day for a cat. Short to no time spent in a fridge with a weak lid. People do not want to have an opened can of cat food leeching stench into their fridge for long periods of time. No "reusable" lid I ever found could keep the smell out instead of ziplock bags, which get slimy and nasty if your reuse them but then you're constantly buying more bags.

A majority of the market won't buy bigger cans because they prefer the convenience of one time, limited use to potentially having your fridge smell like low quality fish and chicken product gruel.

But that doesn't make for an interesting response to the ravings of an uppity math professor. They didn't quite feel like trying to explain the habits of normal, regular people to a lunatic is worth their time. So they decided to have a laugh in kind.

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