Caring for Clay Pots (or Claypots)

[rancho_gordo]

Amy suggestions for a fixing a developing crack? I smeared Elmers Glue up and down and it seems to be fine. This is an unglazed cazuela. I'm going to try and use it tonight but I wonder if there are expert ideas.

[Wolfert]

For the la chamba pots and Spanish cazuelas: If the crack is in the inside, simmer some milk in it. If it is on the outside submerge the cracked part ina wide pan filled with milk, bring slowly to a boil, and cook 1 hour. The crack should weld itself together, or so I am told.

Manka of Manka's restaurant in Inverness confirmed that she simmers her pots in milk to keep them as strong as new.

[Smithy]

<snip>

I'm still curious about some of the issues I raised in the first post, though.  Is it in fact possible to cook over an immediate medium heat, with nothing first in the pot, as is done in the Bittman recipe I linked to?  If so, why does everyone say not to do these exact things?  If not, then did Bittman just err in suggesting this recipe for a clay pot?

←

I'd be leery of trying it, Mark Bittman notwithstanding. I just looked at the recipe and wondered whether he really meant to bring the pot slowly up to medium heat before adding the pork, rather than immediately plunking the room-temperature pot down on a medium-heat burner. I really think one of the keys to protecting the pot is making gradual changes to heat. I am deliberately not defining "gradual" because I don't know the numbers, but I've been monitoring it by checking the bottom of the pot vs. the sides. If I note a big change in one without a corresponding big change in the other (this applies to rapid cooling, too) I get that pot onto a potholder or wire rack to stabilize.

Here's the issue: clay isn't a very good heat conductor, and that means that if you heat one portion it takes a while before the rest of the pot catches up to the same heat. If you heat the bottom quickly, it will start to expand before the sides have begun to warm up and expand. CRACK! If you concentrate heat only on the center portion of the bottom, then the outer rim of the bottom will take a while to catch up and start expanding, and again, you'll get a crack. If the pot's thick enough and you put it over high enough heat, you might even get a crack through the bottom because of the outside expanding more quickly than the inside. The trick is to make gradual changes to the heat so the heated portion can pass the heat to the nearest unheated portion, which passes it on to the next unheated portion, and so on. Each portion has to have time to react by expanding, and if there's too much difference in the amount of expansion then you'll get a crack.

Heating clay pots vs. metal pots is a bit like relaying a message 10 times and comparing the transmission rates and reaction times of different communication methods. Good metal conductors such as copper and aluminum relay the heat with the lightning speed of forwarding an email 10 times. Clay is, well, more like trying to relay a message through 10 successive post offices...or maybe even the Pony Express.

Edited March 23, 2005 by Smithy (log)

[Avumede]

Great post, Smithy. Taking what you said farther, I'm going to assume that the reason you want liquid in the pot is to help the heat to diffuse both more gradually (since the liquid will have to be heated up), and more evenly (since the pot is partially filled with liquid, therefore touches more of the clay pot). Perhaps, though, a slow enough heat may obviate the need for liquid. In that case, Bittman's recipe could work if done slowly enough.

[Wolfert]

Thank you so much for that post.

SMithy;When I am simmering on low using an earthenware pot that is completely glazed I can keep the temperature of water stable for hours. I could never do that with copper or cast iron. Can you explain?.

By the way, check out the 'simmer mat,' abn import from New Zealand. It is the best heat diffuser I've ever worked with.

Edited March 23, 2005 by Wolfert (log)

[Smithy]

Thank you so much for that post.

SMithy;When I am simmering on low using an earthenware pot that is  completely glazed I can keep the temperature of water stable for hours. I could never do that with copper or cast iron. Can you explain?.

By the way, check out the 'simmer mat,' abn import from New Zealand. It is the best heat diffuser I've ever worked with.

←

I have a couple of guesses about the stable simmering temperature. First off, are you simmering over coals, gas, electric coil, or all of the above? I'm going to guess that you're referring to simmering over coals or coils, which will have a certain amount of temperature fluctuation, and that the effect isn't as noticeable over a steady gas flame. Am I right? If so, then what you're probably seeing is the heat content of the pot steadying out the fluctuations in the heat source. For instance, coals will burn out and have to be replaced, and there are bound to be changes in the temperature despite your best efforts as you add and move coals around. It has been noted in other threads that electric coils generally cycle on and off to maintain a low temperature - I doubt you have those, and I have to say I haven't seen mine doing that, but I certainly have seen my electric skillet doing that. (Drives me nuts, it does.) When that happens, the pot will want to transmit the heat change to the water. Water is pretty slow to respond to heat changes, but we all know it does. That's where the efficiency of heat conduction, and the total heat capacity of the pots in question, come in. The more efficiently the pot material conducts heat, the more quickly the water temperature will respond. The more thermal mass (heat capacity) the pot has, the more slowly it will change temperature, even if it's a good heat conductor. As an analogy, I'll use cars, something I have on my mind right now because of the gigantic frost heaves in our local roads at this time of year. Heat conductivity is like the suspension on your car: good heat conduction is like a stiff suspension that "lets" you feel every bump in the road; poor heat conduction is more like a nice soft suspension with good shock absorbers. Thermal mass (heat capacity) is like the weight of your car: the heavier it is, the less it will jump up and down with the bumps; the more heat capacity, the more heat the pot soaks up before it changes temperature. So, when I drive down the road in our heavy company pickup with cushy suspension, I hardly feel the bumps. That's like the clay pot, taking its own sweet time to register and transmit changes in the cooking heat. When I drive the same road in my Geo Tracker (I swear that thing has 2x4's for shock absorbers, and it's a very light car) I get jolted from here to tomorrow. The cast iron pot is likely to be "heavier" thermally speaking than the copper, and maybe heavier than the clay (that's a test I plan to do soon) but it still conducts heat jolts better than the clay does.

I said I had a couple guesses, but after that dissertation I'd better stop and check. Do you see the same phenomenon with gas? I'd expect that to be steadier, so I'll have to think of another explanation if you get the same effect regardless of the heat source.

I notice that you specify "a completely glazed pot". I assume that's because you lose water from unglazed pot as we've discussed above, and have to keep adding?

[fifi]

Cool analogy with the cars and trucks. I may have to use that. I think you are right on about the heat sources as well. Clay steadies everything out. But it is those properties, particularly poor conductivity that can get you into trouble with cracking.

There is one other phenomenon that I have seen with glazed pottery and it happened to me. I put some coffee into a stoneware cup and put it into the microwave. KERPOW!!! It was a hand thrown cup made by a friend of mine and the clay was fairly porous. A crack had developed in the glaze that I did not notice. Actually, the reason I put it into the microwave was the coffee had been sitting in the cup a while. Enough coffee seeped into the clay to cause a steam "explosion."

BTW . . . Beware of microwaves with any kind of pottery or stoneware (not porcelain usually) because they can really heat up. In fact, I read somewhere that a good test to see if dishes are "microwave safe" is to put some water in a cup or bowl and nuke. I forget for how long, but I am sure is was a minute or under. If the dish itself gets hot, it is not microwave safe.

[Smithy]

Thanks!

I'm glad you brought up the "microwave-safe" dish business. I always thought I'd heard that if the dish heats up in the microwave it had lead in it and shouldn't be used for food. That never made sense to me, particularly because my Mikasa everyday dinnerware gets pretty hot in the microwave and I'm quite sure it isn't leaded. Are you saying the microwave-safe business is to prevent cracking and explosions?

Somewhere around here in another thread, there's a pointer to the "exploding water" phenomenon in a microwave oven. The basic explanation is that water can be superheated in the microwave if its oxygen content is low enough (for instance, if it's already been boiled once), and as soon as you disturb it or drop something into it the steam bubbles can form abruptly, and rather explosively. At last I know why those bubbles form so vigorously when I heat water in the microwave and then drop a teabag in. I quit doing that because it never made good tea. I never realized there might be a safety issue if I carried it far enough.

OK, back to clay cookware...

[fifi]

I never heard the bit about the microwave heating being about lead. I always assumed that the chemical make-up of the clay used is the cause. That varies all over the map.

(And the superheated water thing happened to my daughter. Nasty burn, too.)

[fifi]

My new Rifi tagine has arrived and is now reclining in a tub of warm water. Off to get some chunk charcoal to make ashes.

[gingerly]

my 2 bits- i suspect it's more likely iron in the clay body.

[Smithy]

I feel like y'all should be sending out cigars to celebrate the new arrivals. Congratulations!

[andiesenji]

I bought one of the Chamba pots and soaked it for an hour.

Part of the handle on the lid crumbled away. Has anyone else had that happen?

[Richard Kilgore]

Not mine. I suggest you email or call Nidia.

[Wolfert]

Yes, telephone her at once.

I never heard of that happening.

Let us know what she says.

If Nidia doesn't have a good reason, you might try the Santa Fe Cooking School. They use them all the time and have some pointers on their care. I know they don't want you to put the chamba in the dishwasher.

[andiesenji]

I did not get my La Chamba pot from Nidia. It came from a local restaurant that imports them from Columbia (one of the owners goes home twice a year and brings back supplies and ingredients he can't get here in the states.)

My Spanish is not so good and the other owner, from El Salvador, has some English but we had some difficulty in communicating. He said to soak the pot for half an hour or so - I didn't realize he didn't include the lid in the soaking instructions. I should not have soaked it.

My pot is a bit different from those sold by Nidia. The handle on the lid is a loop instead of a knob.

The pot itself is fine and I used it on the gas stove with no problems, after I finished the "curing" and cooked some milk in it.

Edited April 6, 2005 by andiesenji (log)

[Wolfert]

I am so relieved.

I keep my chamba pots as well as the unglazed Moroccan pots lightly rubbed with oil.

[jons]

Paula,

The tagine has arrived and my neighbor has donated about twenty pounds of ashes. To cure the tagine, I plan to soak it in water for two hours and then rub the inside with olive oil and the outside with a mixture of olive oil and ashes. Then, I will bake it at 350F for two hours, starting in a cold oven. Is this correct?

I know this is a silly question and most of it has already been covered in this thread, but for some reason I'm paralyzed by tagine insecurity.

Also, if the tagine is not used for a considerable period of time, does it need to be reseasoned?

[Wolfert]

This is a cosmetic application to rub it inside and outside with an oil and ash mixture. You might want to wear plastic gloves because this is messy job. I estimate you need about 3/4 cup wood ash and 1/2 cup olive oil for a one time application. Keep the rest of the wood ash, you might want to repeat this step for a deeper "tanning." I think I did it more than twice.

Please do post a photo.

As far as I know you only need to soak the tagine once.

Edited April 11, 2005 by Wolfert (log)

[Aquitaine]

Great thread, everyone -- thanks from this lurker-soon-to-be-an-owner-of-claypots (due solely this thread and related such as the tagine pot and Moroccan cooking threads)...

A little late to the party, but for those of you interested in purchasing the heat diffuser that Paula Wolfert refers to above on this same thread ...

Posted by: Wolfert on Mar 23 2005, 11:48 AM

Thank you so much for that post.

SMithy;When I am simmering on low using an earthenware pot that is completely glazed I can keep the temperature of water stable for hours. I could never do that with copper or cast iron. Can you explain?.

By the way, check out the 'simmer mat,' abn import from New Zealand. It is the best heat diffuser I've ever worked with.

...it is called the SimmerMat, and the website for its New Zealand distributor has this to say about it: ...©SimmerMat™ has won an "Industry New Zealand Award" in December 2000, and in January 2002 for business innovation that has the potential to strengthen New Zealand's economy. It has just won an Award in the Cookware/Bakeware Category of the New York Gourmet Show as "Best New Product Award 2004" on 25 October 2004...

I spoke with the US distributor, IMCG Inc. (877/381-7259; Email: info@imcg.us, www.Imcg.us) and was told that both the Solutions Catalog and the Bakers Catalogue should carry it. Just ordered mine today, Item #68245 at Solutions Catalog: http://www.solutionscatalog.com/jump.jsp?i...iProductID=5144

[Wolfert]

I'm glad you brought up the "microwave-safe" dish business. I always thought I'd heard that if the dish heats up in the microwave it had lead in it and shouldn't be used for food. That never made sense to me, particularly because my Mikasa everyday dinnerware gets pretty hot in the microwave and I'm quite sure it isn't leaded. Are you saying the microwave-safe business is to prevent cracking and explosions?

Earthenware which is not fully glazed should never be used in a microwave since, if the clay is wet, steam formed in the center of the clay can cause it to crack or even explode. This is not a concern in the oven since the heat is more gradual

[seabream]

I have heard about so many different ways to season unglazed clay pots, and I'm wondering about the science/reasoning behind all of these techniques.

I understand that unglazed clay pots need to be seasoned so that they don't crack in the first use. But how exactly does olive oil, garlic, vinegar or molasses contribute to that goal? And is this the only reason why we season them?

Thanks in advance for any replies!

[weinoo]

I've seasoned my clay cazuelas by just soaking them in water to cover overnight, and then heating them slowly in a 300 degree oven.

Here is what La Tienda.com has to say about "curing" a cazuela...

Soak the entire dish in water to cover for 12 hours. Drain and wipe dry. Rub the unglazed bottom with a cut clove of garlic (we are not sure how the garlic works, but why argue with tradition?) Fill the dish with water to 1/2 inch below the rim, then add 1/2 cup of vinegar. Place the dish on a flame-tamer over low heat and slowly bring the water to a boil.

Let the liquid boil down until only about 1/2 cup remains. Cool slowly and wash. Your cazuela is ready for use - the garlic has created a seal. This technique has been used since the middle ages. It seasons the pot, kills bacteria, and hardens the unglazed parts.

Especially if you intend to use the cazuela to cook strong flavored fish or seafood, after soaking, rub the inside of the base and lid with olive oil and put into a preheated 300 degree oven for 1.5 hours. Turn off the heat and let cool. Either method will strengthen your cazuela.

I imagine there are a variety of methodologies for your perusal out there on the internet.