Bean plating technology for canned beans
September 19, 2012 1:07 PM   Subscribe

Before I cook dried beans I sort through them usually finding and discarding a clod of dirt, a small stone, or a moldy bean. I have never found a stone in a can of canned beans. Are the canned bean manufacturers sorting the beans before canning? If they are, why can't they use that technology to clean the beans that are sold dried? The tedious sorting keeps me from cooking beans from scratch as often as I'd like.
posted by SandiBeech to Food & Drink (15 answers total) 2 users marked this as a favorite
I don't know for certain, but I have two theories:

1. Beans swell up when they cook; a stone wouldn't. This may make it easier to sort out stuff post-cooking.

2. Maybe they aren't, and you've just been lucky enough to get the cans without crud in them.
posted by EmpressCallipygos at 1:16 PM on September 19, 2012 [1 favorite]

By canned beans I assume you mean cooked beans in some sort of liquid, right? If you are allowed to get the beans wet, you can sort stones and dirt out by density: less dens beans will float in water (or other appropriate liquid), dirt and rocks will fall to the bottom - pretty easy to implement as an industrial process, but it won't work for dry beans.
posted by Dr Dracator at 1:16 PM on September 19, 2012 [5 favorites]

I don't eat beans very often, but my mom used them a lot when we were growing up. I was always amused by how many stowaway twigs and pebbles there were in the bean bag.

My mom's method never seemed too tedious: fill up a bowl with water, dump in the beans, and give them a swizzle. Once things settle, the twigs will be very obvious up at the surface, and the dirt and pebbles will fall to the bottom. Pick out the twigs, then skim the beans off the top of the water. Do what you do with the beans. Dump the rest.
posted by phunniemee at 1:25 PM on September 19, 2012 [1 favorite]

dirt and rocks will fall to the bottom
not very small rocks.

Typically production of process food is more highly regulated than raw goods. I betcha they are required to scan for debris before processing.
posted by Gungho at 1:26 PM on September 19, 2012 [2 favorites]

Cooked foods are subject to regulations that raw foods are not; namely, you can't have large pieces of foreign matter in cooked baked beans.
posted by dfriedman at 1:29 PM on September 19, 2012 [2 favorites]

This canning manual (link is to a pdf) says that all canned foods have to be cleaned, and outlines some of the methods that are used to do so.

Canned beans are a lot more expensive than dried, per unit cooked weight. Cleaning is one part of the process that raises the price.

Incidentally, in Pakistan, regular grocery shoppers know which stores carry cleaner legumes. The cleaner ones are invariably more expensive; some people find the convenience worth paying for, others do not.
posted by bardophile at 1:32 PM on September 19, 2012 [2 favorites]

The cannery investment in sorting machinery might be one of the reasons that dry beans are less expensive than canned beans.

Dr. Dracator's argument that sorting is much easier to do in water is true - but that doesn't hold up in practice, since it's easy to give dry beans a rinse and then then let them dry out again before packaging. Or maybe that's a stage of processing that isn't worth the investment. I have noticed that some brands of beans are stonier/twiggier than others.
posted by aimedwander at 1:33 PM on September 19, 2012

Maybe try several different brands of dried beans to see if some are cleaner than your normal brand? I don't know how dried beans are cleaned industrially, but there seems to be a good process which some companies use. I've noticed quite a difference in pebble/mud clod frequency, and although I always give beans a once-over I haven't found anything that shouldn't be there in the more expensive brands. This includes supermarket house label beans; "expensive" is relative, here.

A very good clue is if the beans look shiny or matte/dusty in the bag. Dusty beans are invariably dirty - the rinse water will be grayish and there are often pebbles (mud clods dissolve). I don't know every type of bean, but the ones I cook have smooth skins with a silky luster. If they don't look glossy I won't buy them. This doesn't apply to legumes without skins (like split peas), but even there a certain grayish dustiness is a bad sign.
posted by Quietgal at 1:34 PM on September 19, 2012

A friend worked 'on the line' at a small farm-to-freezer company in Washington State back in the early 90s. The produce would be examined by several people as it crossed on a conveyor belt, then went in for sifting (screens of various sizes) and then it went into packs for the cooking and freezing parts and more examining. Peas and corn were the worst - peas due to the nightshade which grows in with the plants and corn was messy due to the milk.

Then again, I just bought a 5 pound mix of ten different fresh shelled raw beans straight from a farmer and it was pretty clean of debris. (at $3.00 a lb, it was much more expensive than dried too)
posted by jaimystery at 1:35 PM on September 19, 2012

Maybe switch brands of beans? I cook dry legumes 1-2 times per week (almost exclusively bought in the bulk section at my co-op or in bags at the indian grocery), I never ever sort, and I've never bit down on a rock. There must be some kind of variability in the sorting process.
posted by juliapangolin at 2:06 PM on September 19, 2012

I'll bet that Cyclonic Separation is involved.
posted by Confess, Fletch at 2:42 PM on September 19, 2012

I have never found strange junk in the higher quality, more expensive dried legumes. We get bulk Rancho Gordo beans at our Whole Foods. They're expensive. However they taste great and I've never found dirt, pebbles, or anything else. If I buy cheap beans there's usually a twig or dirt clod.

Industrial bean processors have automated sorting and sifting. It's cost effective for them to do so, because of the markup on canned food. Less so for producers of dried legumes, especially those that are not selling in the high-end market.
posted by oneirodynia at 2:43 PM on September 19, 2012

The price of a pound of canned beans is what, a dollar? That pound is like, a handful of dried beans plus a whole heck of a lot of water and a can. I am quite confident that the reason the cheap dried beans have dirt, stones, and bits of twig is because they can sell them that way, and save money, and therefore charge less.

Those who mention that you're just flat not allowed to sell cans of beans with rocks in them also raise an excellent point. You can't have dirt on bagged lettuce, or in canned sweet corn, but you get it in the fresh stacks of those same vegetables in the same store.
posted by SMPA at 4:36 PM on September 19, 2012

Dried beans will vary a lot in cleanliness because I think there's a transition from mechanical air and screen cleaning machines to cleaning first with air and screen machines and then colour sorters, which have some optical sensors that detect material that is a different colour. An air and screen machine sorts by weight and size, so stones and dirt the same size of the beans don't get cleaned out. But a colour sorter can catch those. And yes, when the beans are canned, the water would get that stuff out too. I don't think it would be feasible to wash and dry dried beans because it would affect their quality/storage life.
posted by bluebelle at 6:47 PM on September 19, 2012

I think the magic step which allows the canned bean producers to sort all the twigs/stones/etc crap out involves getting the beans wet and letting them float. It's pretty trivial to get the stones and stuff out of dried beans once you put them in a pot of water, but not before. But obviously you aren't going to get dried beans wet. So they just package 'em up and let you do it, instead.
posted by Kadin2048 at 10:42 PM on September 19, 2012

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