Curling ganache! Help?

Having made a ganache I pour it into a frame (37.5cm x 37.5cm x 1 cm /
15" x 15" x 2/5ths"). The frame sits on an acetate sheet, which in
turn sits on a stainless steel tray. I then leave the ganache to
crystalize for 24-36 hours in an air conditioned room at 17 degrees
Celcius (62.5 degrees F).

24-36 hours later, I remove the frames and coat the top of the ganache
with a thin coat of tempered couverture. Once this has set, the sheet
of ganache is cut with a guillotine into 256 squares, each just under
1" x 1".

My problem: the sheets of ganache are curling up at the edges during
the crystalization period. Some of them are spliting into two or more
framgents. Then the problem gets worse once the sheets are coated with
tempered couverture. Any thoughts as to what is going wrong?

I used to get this with the occasional sheet, now I seem to be plagued
by it. For information (should it be relevant): The current relative
humidity is just over 50%; my ganaches are made with approximately 9
parts cream to 10 parts couverture. This seemingly 'wet' ganache ratio
is partly for reasons of taste, and partly a peculiarity of using
Valrhona's grand cru couvertures - a 1:2 ganache resembles a brick in
texture - honest!

Many thanks
Simon

Simon Mitchell wrote:
> Curling ganache! Help?
>
> Having made a ganache I pour it into a frame (37.5cm x 37.5cm x 1 cm /
> 15" x 15" x 2/5ths"). The frame sits on an acetate sheet, which in
> turn sits on a stainless steel tray. I then leave the ganache to
> crystalize for 24-36 hours in an air conditioned room at 17 degrees
> Celcius (62.5 degrees F).
>
> 24-36 hours later, I remove the frames and coat the top of the ganache
> with a thin coat of tempered couverture. Once this has set, the sheet
> of ganache is cut with a guillotine into 256 squares, each just under
> 1" x 1".
>
> My problem: the sheets of ganache are curling up at the edges during
> the crystalization period. Some of them are spliting into two or more
> framgents. Then the problem gets worse once the sheets are coated with
> tempered couverture. Any thoughts as to what is going wrong?
>
> I used to get this with the occasional sheet, now I seem to be plagued
> by it. For information (should it be relevant): The current relative
> humidity is just over 50%; my ganaches are made with approximately 9
> parts cream to 10 parts couverture. This seemingly 'wet' ganache ratio
> is partly for reasons of taste, and partly a peculiarity of using
> Valrhona's grand cru couvertures - a 1:2 ganache resembles a brick in
> texture - honest!
>
> Many thanks
> Simon

I can think of many reasons why this might be happening (surface tension,
contraction as the ganache and couverture cool, differences in adhesion to
the frame and the acetate, differing rates of moisture loss at the edges and
the center of the sheet, etc.), as I'm sure can you. I visualize the way a
piece of soft bread, left out to dry, curls up at the edges. The same thing
happens with watercolor paper when it is moistened and left to dry if it
isn't taped down around the edges.

I would suggest--although I doubt you'll like the answer--that you would be
less likely to have this problem if you made your ganache layer somewhat
thicker. The increased mass might help.(This doesn't happen to me when I
leave 10x10 sheets of ganache to set, but they are about 1/2" thick. How
thick yours would have to be I do not know.) Another solution might be to
evenly weight the entire sheet between two layers of acetate as it sets
(Although I would think that this would lengthen the time involved). Or, of
course, to change the composition of the ganache. (Another thing I know you
don't want to do.)

Another solution might be to take steps to even the drying times of the
edges and the center, perhaps by applying a "frame" piece of acetate that
overs only the outer few inches of your ganache sheet (rather in the way
Magic Cake Strips insulate the edges of a cake pan and so encourage even
rising throughout).

As it happens, I have had a similar problem with a set of molds I own. It is
a very long and narrow shape: separate stalks of asparagus. I line the mold
with dark couverture, fill it for most of its length with a thin line of
flavored ganache, and then seal the backs in the usual manner. When it is
set, the ends have usually curled up slightly, just enough so that I cannot
put two stalks together back to back, as intended. And quite often the
pieces will have cracked across just below the head of the stalk (the
narrowest point). As a result, I've never been able to use this mold for
producing the items I had in mind. I'm hoping that a solution for you can
shed some light on this problem also!