The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Flour Mill/Grind Stones - Real Stone vs Ceramic Corundum / Carborundum (i.e. Sandpaper)? is Abrasive in our food SAFE?

Nick Sorenson's picture
Nick Sorenson

Flour Mill/Grind Stones - Real Stone vs Ceramic Corundum / Carborundum (i.e. Sandpaper)? is Abrasive in our food SAFE?

I'm very much into wood working which involves some hand tool sharpening. In the sharpening world, we're very familiar with abrasives. Some people use sandpaper taped to a piece of plate glass or a flat granite tile working from course (say 400) to fine (say P2000 wet). Other people use a wet stone which is basically a block of adhesived together Aluminum Oxide (the main ingredient/abrasive in most sandpapers). Others (including me) prefer natural stones to sharpen with. I like them because they're VERY hard and don't wear out. The other methods use grit particles which wear away in a slurry of tool steel and abrasive particles/binder as the tool is sharpened. It's not a big deal because you wash the stone off when you're done.

That background given, I don't like the idea most grind stones are using when it comes to flour mills. I don't think most bakers think about it like I just did. But having used abrasives as much as I have (especially with stones and grinders) I don't like the idea of all that abrasive and binder going into my food/flour. I've also heard that dentists don't like the abrasive either (read that it can effect tooth enamel). Not to mention eating aluminum... I know... I know... they say it won't hurt but still... it's aluminum! Most home flour mill grinder manufacturers call it Ceramic Corundum but from what I've read (including the Wikipedia on "Corundum"), that's just another name for Aluminum Oxide. I've seen this in several places so I assume this to be the case. It makes sense, most stones for grinders (bench grinders for instance) are made using Aluminum Oxide as the abrasive.

But long and short of it, does this bother anybody else? I personally don't like the idea. I'd really like to find a real stone grinder if there is such a thing. Maybe it's not a big deal regarding our health but I'm curious.

The stones I use for sharpening tools (and my food knives) are Arkansas Oil Stones made by Hall's Pro Edge. I really have been happy with them. I use diamond for the course roughing out and switch to a black oil stone for the final edge. Works great! That's unrelated but part of what got me thinking about the stones in grinders.

Nickisafoodie's picture

Try a wonder mill or similar high speed impact mill, cost about $250.  They work great, keep the flour cool, and even a medium setting makes fine flour.  No sharpening or other maintainence needed, and faster thruput too...  Been using one for 15 years regularly and it is still going strong.  use the search box in upper left corner and you will see lots of postings on mills... 

Good luck

varda's picture

I just did a google search and this old TFL post popped up:

suave's picture

You have to understand the difference between ceramic and abrasive. 

pmccool's picture

Of course, then you'd have the concern of microscopic metal particles in your food...

Not to put too fine a point on it, but everything we eat has something in it that is harmful to our bodies, if we eat too much of it.  That last phrase is the kicker.  If our water supply has high levels of naturally occurring arsenic in it, that's not a good thing even though it is 100% natural. 

Natural stones in mills are just as prone to wearing as man-made stones, which is why they often need to be re-dressed after extended use.  Where do the worn parts go?  Into your flour and then into your body.  They will wear your teeth as much as the carborundum particles, which is to say not much.  This was a big deal in many communities hundreds of years ago if the local mill used stones that tended to wear rapidly, or if the miller was not managing the mill properly.  In such cases, the flour contained high levels of grit from the stones and peoples' teeth suffered greatly from wear.  Nowadays, with most of our flour produced by steel roller mills, it's a non-issue.

So, continue your studying, figure out what sounds scary (but isn't) and what truly is scary, and make your choice accordingly.  My opinion is that any of the choices mentioned so far will produce good flour with minimal risk to you, the user.  You may come to a different opinion.  Either way, enjoy your freshly ground whole-grain flour.


Nick Sorenson's picture
Nick Sorenson

Hi Paul,

You mention that natural stones will wear just as much as synthetics, I don't mean to argue for the sake of argument of course and I agree with a lot of what you said especially the part about everything has something harmful the key is not to eat too much of it. The solution to polution is dilution.

But back to natural vs synthetics... this is with sharpening stones as a basis (don't know if it applies 100% to mill stones but I certainly would think that it should), but natural stones stay perfectly flat basically for the life of the stone where-as the water stones (synthetics using alum ox) have to be dressed/re-trued to flat regularly. The reason for this being, as mentioned in the original post, there's always a slury of aluminum oxide and binder/adhesive that's worked loose from the stone during sharpening. With a natural oil stone, there's basically (for all intents and purposes) ONLY the metal from the edge that was sharpened and that's it. 

So the two do wear quite differently and with natural stone wearing hardly at all. You definitely don't see the particulate like you do with the synthetic stones. And if you've sharpened tools or knives with a wetstone, you know that it's quite a bit that breaks loose. So it's quantity of particulate/foreign matter that I think would be the biggest difference besides the safety of the material itself.

pmccool's picture

One base assumption you have mentioned is that milling produces the same slurry on the surface of the stone as occurs during tool sharpening.  That does not happen during milling.  If it did, no one would use a man-made material for a millstone because the inclusion of abrasive material in the flour would be intolerable.  

Grains, even harder types such as durum wheat, are significantly softer than metal.  Consequently, they do not wear the burrs as much as does a metal tool.  It is absolutely true that wear occurs.  However, the amount of wear from one mill run to the next wouldn't be visible to the unaided eye, whereas tool sharpening produces visible wear during each use.  From what I have been able to find on-line (it's a bit dubious since most of the sites are by manufacturers or their resellers), the corundum-ceramic stones are advertised as having about a 15 year life and granite stones are advertised as having about a 20 year life.  That also points to a low rate of wear for the synthetic stones and a correspondingly low deposition of the stone material in the flour.

Please understand that I'm not trying to steer you toward a material that you are uncomfortable to use.  Just be sure that you don't extrapolate the outcome from one type of use (tool sharpening) to the outcome of a very different (grain milling) use.  And be sure to discern whether the material used for sharpening blades is the same as, or different than, the material used in millstones.  Even if the abrasive material (carborundum, corundum, or other) is the same in both uses, I suspect that the substrate or matrix in which the material is housed is very different and therefore leads to a different outcome.


Nick Sorenson's picture
Nick Sorenson

This makes complete sense. I am used to a HUGE mess with waterstones and edge tools/knives and much less mess with the natural arkansas oil stones. So I just pictured the wetstone (synthetic) mess carrying over to grinding wheat. I suppose it's probably to a much lesser degree with wheat. Didn't think about that point. Thanks for mentioning it. If I had the choice between a rock with it's God given bond vs a bunch of abrasive particles held together by glue, I'd pick the rock's natural adhesion any day. But for the most part, it looks like all home level grinders that use a "stone" pretty much have a man made abrasive as far as I can see. BUT... maybe it's not that big of a deal when grinding this soft of a medium (wheat).

MangoChutney's picture

No, this does not bother me.  I am not keen on eating any kind of grit in my food, but whatever may be coming from the synthetic burrs in my Wolfgang mill is apparently too fine to bother me if it even exists.  Sharpening metal tools and grinding grain are not the same.  Corundum is much harder than grain and the plates are not supposed to be allowed to touch so they don't grind each other.  I have seen a fine dark powder resulting from running the mill with the plates adjusted too close together.  This does not seem to appear when the plates are properly adjusted, nor when grain is added with properly adjusted plates.

I use my Wolfgang mill daily for making breakfast, every five days to make bread, and occasionally otherwise.  Breakfast is 1/3 cup oat groats milled with 1 tablespoon flax seeds, which does not clog my mill as long as I mix the two well.  I have even begun lately to mill the combination on my finest setting, which I had previously avoided because even oats alone has more fat content than other cereal grains.  Flax alone even at a coarse setting will indeed clog the mill.  However, it is easily cleaned if this should happen.  The worst part is cleaning up the flax seeds from the counter top when you turn the mill upside down to dump them out.

As for whether alumina is toxic, I don't believe that it is.  Differing oxidation states of metals behave very differently, as do differing salts.  As an example, you eat sodium chloride and in fact must have some of it in your diet.  Sodium bicarbonate is baking soda.  Sodium carbonate is washing soda, and can be used to coat pretzels and bagels.  Sodium hydroxide is used to clean out drains, and for the previously mentioned coatings if you are brave.  Sodium metal reacts with water to form hydrogen which can easily explode due to the heat created by the reaction.  Alumina is a fairly innocuous salt of aluminum.

sonika's picture

Maybe you should consider the Samap hand grain mill. Here is the link for you guys to look at:

I found it while doing research in order to decide what kind of mill to get (still undecided). If anyone has prior experience with it, please enlighten us on the stone wear. I,  too, am concerned about the unwanted materials that end up in the flour as a result of milling parts wear. In case anyone is interested, I have opened a topic about the subject here: