Röhmertopf?

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Hi folks

Hubby is giving me new challenges. This time, he has asked me to make a
röhmertopf.

I have started, but now I am having misgivings. The clay I use is a
high-fire clay that can be fired to 1350 C. But I know that it has to be
low-fired (1000 C), in order to be able to absorb some of the humidity it
needs.

Since it has to be unglazed, I have been "burnishing" it - ie. rubbing it
with a rubber rib, so that the surface is very smooth - also thinking this
will make it easier to keep clean.

But then it hits me.... maybe I am then causing the surface to be more
sealed and impenetrable, which would work against the idea of the pot
absorbing moisture???

I read on the net that the original Röhmertopfs are made of a special clay.
Will my clay work anyway? or should I just chuck the whole thing into my
recycle bin now? :-)

Marianne



Re: Röhmertopf?

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We were given one as a wedding present.  It appeared to be made from just
terracotta clay.
My sister in law makes what she calls chicken bricks.
She throws a large, tall oval shaped pot and completely closes it off.
Turns it so that it is nice and oval, then turns it on its side and flattens
a base, then cuts a lid.  She then uses it for cooking like the rohmertopf.
She just uses a basic terracotta.
A



Re: Röhmertopf?
The ones I have seen also seem to be just terra cotta.  I think terra cotta
is fired to about 2000 degrees F (1100C).  That is way beyond what you are
going to get in an oven.  You just don't want it to go through thermal shock
(go on to a cold shelf such as the refrigerator after coming out of the
oven).  Special clay is needed for using on the stove top for this reason.
In the oven unless it is directly on or under the burner this isn't going to
be an issue.  Also don't you start the dish cooking in a cold oven?

Donna

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Re: Röhmertopf?
P.S. This may be what was meant by using a special clay body.  Still you
aren't using a glaze so fit isn't an issue and as long as you don't go from
one extreme temperature to another using terra cotta shouldn't be a problem.
I also wouldn't just chuck your piece.  You can always use it as a test
piece and surely there must be other uses for it if you decide not to use it
for the oven?  You can still glaze it even though it has been burnished if
that is what you would like.

http://www.digitalfire.com/education/glossary/ (digitalfire is a must have
link)

Ovenware
Ovenware (and flameware) clay bodies have a lower thermal expansion so they
can withstand more sudden changes in temperature. Ovenware bodies should
thus have much lower free quartz content and employ low expansion minerals
like mullite, pyrophyllite, petalite, kyanite and spodumene. While many
potters make ware for use in the oven using standard clay bodies, ovenware
manufacturers (like Corning) would object to calling this 'ovenware'. This
is because they dedicate considerable resources to producing bodies and
glazes that have a much lower thermal expansion and therefore are much more
suitable. Potters are able to get away with using standard bodies and glazes
by making sure the glaze fits well (no crazing), avoiding high-quartz and
highly vitreous bodies, firing evenly to reduce built-in stresses,
maintaining an even cross section, avoiding angular contours and larger
sizes with broad flat bottoms and telling customers to be careful about
subjecting ware to sudden temperature change.

Glaze fit is a major problem in designing an ovenware body since common
glazes will craze. It is much easier to make a low expansion clay body than
a glaze, thus it is normal to compromise the lowest possible expansion on
the body in order to get a reliable glaze fit. Low expansion glazes
typically employ lithia and high silica and alumina and avoid sodium and
potassium. It is much easier to make a low expansion glaze at high
temperatures where silica and alumina can be higher.

There are two mechanisms to creating a low expansion body: By firing to form
crystalline minerals that have low expansion or by employing mineral
particles and fluid glasses in the body recipe have low expansion. The
former produces a more vitreous body and requires much more expertise and
test equipment. The later is a bit of a 'crowbar' approach and is dependent
on not firing to full maturity (otherwise mineral species can be dissolved
by the feldspar in the body and the low expansion effect lost). The latter
creates a bit of a 'tug-of-war' in the body since some particles (like
quartz) want to expand on heating and contract on cooling whereas others
(like kyanite, mullite) want to remain stable. Furthermore, the glass that
glues all the particles together introduces a third expansion dynamic to the
matrix.



Re: Röhmertopf?
Bubbles wrote:
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I had an "original" Römertopf, the bottom part was glazed on the inside,
the top not glazed at all. I used it a few times, and found that it
doesn't do anything which an ordinary pan wouldn't do, it only takes a
whole lot longer. It take hours until ordinary vegetables are done,
hours until meat is tender, if you think of the energy it takes in an
electric oven, i decided, it wasn't worth it and got rid of it again.
If the bottom part is unglazed, it absorbs fat and becomes rancid after
a short time, hence all the Römertöpfe you get really cheat at
fleamarktes. I decided, it was just some kind of fad, and gave up on them.

Schöne Grüsse,  Monika
--
Monika Schleidt
snipped-for-privacy@schleidt.org
www.schleidt.org/MSKeramik
if you wish to write me a mail, remove the number from my user name

Re: Röhmertopf?

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The one we had was unglazed, but we did worry about the hygene thing.  It is
now used as a planter :o)
It was a proper romertopfe mould made with the name across it, a recipe book
etc.
I like the tagines more, the morroccan style casserole, here is one
http://www.crateandbarrel.com/family.aspx?c=520&f=9064
I have made them with the lid handle a bit wider so that you can turn it
over and use it as a serving bowl.



Re: R??????????

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Yeah, probably, but then you clean it as much as you can and let it dry, but
it never looks completely clean again.  Its more a feeling thing probably
than a real hygene issue.  The one here looks very like the one we have,
part of the reason we stopped using it though is because the lid had a bit
crack in it, don't remember how it happened.  It has a little walnut tree
planted in it now, which I must soon transplant to give growing space.



Re: Röhmertopf?


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If the original can be glazed, then so can my "copy". I also like the idea
of hygenic surfaces for food. Might be that temperature kills the bugs, but
I still see a porous surface - yaknow?

I can agree with your arguments, Monika - and also another that this thing
is going to take a lot of space in some cupboard. I have forwarded the
arguments to my husband, and will just keep the whole thing from drying
until we decide what to do. I have non-poison glazes only, so will use one
of the 1000C ones on the inside bottom.

You are supposed to soak the whole thing in water for ages before use - and
then soak for 10-15 minutes before each use - put in a cold oven - and never
on a cold surface when taking out of the oven. Sounds pretty delicate to me!
Hehe!

I'll see what I do - but thank EVERYONE for their ever fantastic responses!
You guys inspire me!

Marianne



Re: Röhmertopf?
They are not supposed to be glazed.  They are supposed to be soaked in water
before putting food in them and then put in the oven.  It is part of the
cooking method.  The food is steamed and then dry roasted which is a bit
odd.  I found that I wasn't fond of mine.  I have heard good things about
the tagines mentioned.

Donna

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Re: Röhmertopf?

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Yeah I prefer the tagines. :o)  They look really cool too and are fun to
throw.



Re: Röhmertopf?

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Do you use yours in the oven or on the stove top?  What clay body do you
use?  I assume they are glazed inside and out...




Re: Röhmertopf?

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In the oven, terracotta, glazed inside, with some glazed decoration out so
that the natural terracotta clay shows.  I have seen some made in quite
grogged terracotta, I guess that would cope with heat changes easier, but
mine survived the oven :o)



Re: Röhmertopf?
http://www.tagines.com/cat_tagine_recipes.cfm

You may have started something.  I am now very much intrigued.  The recipes
on the above are for stove top.  I wonder if they would work just as well in
the oven.  Has anyone used the fireclay that works on the stove top and has
it been successful?

Donna

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Re: Röhmertopf?

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I haven't used them on the stove top as I just used terracotta, they work
well in the oven.  I gave one to friends and they invited us for dinner, it
was very yum.  :o)



Re: Röhmertopf?
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I've made a tagine, several soup pots, tea kettles and a wok from
flameware claybody and they've all been` successful.  The glaze choices
are limited and the clay is a little strange to work with--I found it
to be uncomfortable on my hands, but it was an interesting project.  I
guess the flameware clay is controversial because some people have had
accidents with it exploding on the stove, or developing cracks, but
I've had neither of those things happen to my pots.  They're kind of
heavy though, so I don't tend to use them as much as I hoped.

Deb R.


Re: Röhmertopf?
After looking into it I decided I would rather go with the oven version
(exploding clay shards sound deadly).  I'm glad to hear that there are other
reasons not to use it.

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Re: Röhmertopf?
As a former chef ( now pottery nut and teacher) I found this whole
subject very interesting and thought I might add my 'two peneth' of
knowledge: The idea behind all of these 'oven used' cooking vessels is
that the whole process of cooking is slow, and the effect on the food
might be compared to that of 'heat work' on pots in a kiln. The heat of
the oven will kill most germs (but I can understand peoples'
dislike/distrust of the patina or 'seasoning' that appears on the
cooking vessel); normal cleanliness aplies to these pots as it does
with cast iron, stove top, cooking pans and woks that have 'seasoning',
if in doubt slowly heat the pots (empty and dry) in the oven when using
the oven to do a high temp roast! Low temperature glazes will not make
the vessels more hygenic to use as eventualy all such glazes will have
some (albeit microscopic) crazing which can harbour debree/dirt, more
so than if left unglazed.
This method of cooking does add something to the flavour and texture of
the food; it used to be a great way to cook mutton (a tough but
flavoursome meat) but it's rare to find mutton anymore as most
suppliers sell only year old lamb.
Sincere apologies to any vegetarian readers!


Re: Röhmertopf?
Interesting that you say unglazed is better than glazed, since crazing
actually seems to retain bacteria better than unglazed pottery.

Also, I am wondering if the slow-cooking can just as well be done in a
normal open "pot" with aluminium foil over it at a lower heat? The benefits
of cooking over time are great, that I know. But need we insulate the food
with a röhmertopf in order to get the same effect as simply lowering the
temperature and waiting an hour extra?

My topf is still leatherhard and it can go either way - keep wet, finish and
fire - or wet thoroughly and recycle. I would appreciate your input on the
usefulness of this pot - as compared to the power usage, heavy cleaning job
and storage space required.

Thanks!

Marianne



Re: Röhmertopf?

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Apparently the shape of the Rohmertopf makes the steam circulate differently
which creates more tender moist food.



Re: Röhmertopf?

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Ah bugger, I meant to say the shape of the tagine, with the cone :o)



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