Skippy Skimping Out?
March 16, 2017 12:15 PM   Subscribe

My skipping peanut butter jar's bottom is concave. Why?
posted by INFJ to Food & Drink (8 answers total) 3 users marked this as a favorite
For stability and structural integrity.
Bottle Bases
Why are cans concave at bottom
posted by troytroy at 12:21 PM on March 16 [16 favorites]

This is just guessing, but companies that can only raise prices so high compensate for that by keeping the price the same but lowering the content. (Cake mixes and breakfast cereals shrink in volume pretty regularly, for example, but they keep the boxes the same size and just put less in the inner bags. If you can't hide the contents (like in a clear plastic jar), reducing the volume from underneath is a pretty neat (if insidious) trick.
posted by Mchelly at 12:22 PM on March 16 [5 favorites]

Possibly for the same reason gallon milk jugs have have those dimples?

In case the package is stressed in shipping, there's room for expansion so they don't burst.
posted by sewellcm at 12:22 PM on March 16 [2 favorites]

The issue of shrinking product volume is in this case offset by the fact that skippy jars have had bottoms like that for years now. It's more for stability and keeping the jar stiff with thin walls.
posted by GuyZero at 12:24 PM on March 16 [4 favorites]

It's prob a bit from column A and a bit from column B.
posted by sexyrobot at 12:41 PM on March 16 [6 favorites]

Good question! troytroy has the right answer right at the top. In case anyone wants to know more: this is the same reason wine bottles have an indent, especially sparkling wines. It's called a "punt." These structural considerations are also the same reason high pressure tanks like this propane tank have hemispherical caps, and aren't simple cylinders with sharp corners. In principle they could do peanut butter jars that way too, but then they would fall over, so nobody does that.

Deceptive packaging/shrinking product may come into play, and some brands may have bigger indents than others, but the roots of this are absolutely practical.

Why do these indents and outdents make containers stronger? Sort of the same reason that if you accordion fold an index card, it resists being bent in the perpendicular direction. Also any container under pressure abhors a sharp corner: think of what happens when you blow air into a cubical balloon-- the corners go away. For any more detail than that, you basically have to understand a fair bit of mechanics or be willing to learn about it and things like stress and strain and use mathematical tools like stress tensors. I'm not good enough at that stuff to succinctly summarize it but the links should give you a feel for it and ways to read further.
posted by SaltySalticid at 12:42 PM on March 16 [24 favorites]

It may be due to the Grocery Shrink Ray. Some food companies will add a dimple or a concavity in the bottom of the jar to keep the same visual product size but include less product, so they can charge the same amount but have a lower production cost.

The Atlantic describes the effect and specifically calls out peanut butter.

From personal experience, I have had the exact same thing happen with tubs of hummus.
posted by blnkfrnk at 1:48 PM on March 16 [1 favorite]

This Thrillist article addresses your dimple question. It explains that in 2008, the amount of peanut butter was reduced from 18 to 16.3 oz and the saavy manufacturers changed only the size of the dimple to make up for the volume difference. I am sure SaltySalticid's explanation is correct and also that they take advantage of this lovely hidden dimple to periodically mess with the contents of the jar. For instance, did you notice that your Natural Skippy is 15 oz, 1.3 oz less than the regular?
posted by LKWorking at 3:04 PM on March 16 [3 favorites]

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