I was thinking of getting one of these:
http://www.ebay.com/itm/85-2-Magnetic-Stirrer-Hot-Plate-Digital-Thermostat-300w-Heating-2000-rpm-/350527518368#ht_1652wt_1165

as a makeshift tempering machine.

I plan to put a water bath on the hotplate and put a pot in the water bath.

I would be using it at home to make small batches of chocolate for holidays and such.

Can anyone think of a reason that this wouldn't work? It's a good deal cheaper than a tempering machine and more versatile too. I could just dial in a new temperature and use it for sous-vide or custard or some recipe that would make use of the magnetic stirrer.

updated by @john-doe: 04/12/15 05:58:12

a magnetic stirrer as I know from labs I've worked in will not stir thechocolate very well. You need to make sureyou get all thechocolate off the walls on each stir as most tempering machines do, whereas a magnetic stirrer is a short ~1" bar that will only stir a small area in the bottom center of viscouschocolate.

-Nat

____________________________

Nat Bletter, PhD

Chocolate Flavormeister

Madre Chocolate

http://madrechocolate.com

Hi Nat,

Thanks for your reply. I have a few follow-up ideas I'd like to see if you have any thoughts on.

1) The company that makes this hotplate also sells magnetic stirrers up to 5 cm long. That still won't scrape the sides but at least it's bigger than the standard magnetic stirrer that comes with it.

2) I could conceivably rig up some sort of scraping device which would fit the pan and have the stirrer embedded in it. I'm not sure if the magnetic stirrer would be powerful enough to move such a large attachment though.

3) Maybe something like this http://www.ardentegourmetstirrer.com/ would do the trick?

4) This one is a bit more technical but you seem like the kind of person who would know the answer. Here's my understanding of the tempering process:

Type V cocoa butter crystals will form in the 29-34 C range.If you just let chocolate sit at this temperature all of the crystals will eventually be type V but the time required for this to happen is prohibitive for any commercial confectioner.Agitation will reduce this time, as will various temperature fluctuation or seeding techniques.

So if I'm willing to let the chocolate sit on the hotplate overnight will it still be tempered? Or does agitation play some other role in the tempering process? If I just used a small stirrer and it agitated the chocolate for a long time would the gradual movement and convection near the sides of the container be sufficient to temper the entire mass if I let it sit for long enough?

Any thoughts would be appreciated.

I also think this stirrer would not work as well as you would need it to and I don't think the other stirrer you linked in your reply would do the job either. In my opinion, you'd be better off saving that money for the future and buying a tempering machine rather then spending money of somethingthat probably won't work and/or would be a big hassle.Also, it doesn't seem like you'd be able to temper that much chocolate at once using this equipment. For the amount you could temper using this magnetic stirrer, you'd be just as well off tempering by hand. You can temper a couple pounds of chocolate in maybe 15-20 minutes. To answer your question about tempering, no - tempering is not just about achieving the correct temperature for crystal formation. It most definitely has to do with agitation as well. I highly recommend you know how to temper correctly by hand prior to becoming reliant on equipment. It is a really helpful skill to have. Also, there is a lot of info in JP Wybauw's books about crystal formation, tempering, etc that is good reading. Good luck.

Another problem: What temperature does the hotplate get to? Chances are it gets much hotter than the contents are intended to get, and as a result could burn your chocolate - especially if it's not being moved off of the bottom. Case in point: Even a baine marie will burn your chocolate if you let the water boil and not remove the chocolate from the sides and bottom of the bowl.

My recommendation: If you're going to waste time "rigging up devices" to try and do what's already been invented and proven to work, put in a few more hours at your paying job, save your $$ and buy the right tool for the job - a proper tempering machine. They aren't that expensive.

Brad

There is a cheaper and easier route...

Go to a drugstore and get the cheapest heating pad (electric blanket). The more expensive ones have auto-shut off and terry clothe covers which you don't need.

I just flip over a 1/2 sheet pan on the counter, put the heating pad on top, the bowl or hotel pan of cold couverture on top, and walk away overnight. The "medium" setting is usually pretty darn close.

Stirring is a different matter. Chocolate is thixotropic, which means it is best mixed with a shearing action, any other action for longer periods of time usually incorporates bubbles. Most melters and temperers usually use a wheel/disc with a scraper, or a rotating bowl with a scraper.