The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Baking Stone Pre-heat lag time

davidg618's picture
davidg618

Baking Stone Pre-heat lag time

My wife bought me an infrared remote thermometer for Christmas, and I've been using it much more than I expected. One thing I've noted: my baking stone, a Fibrament, lags behind my oven announcing it has reached temperature. At 500°F it lags by 25 minutes. Other make stones' lagtime will vary, but I suggest 30 min. from the time the oven air temperature has reached the set temperature is a reasonable rule of thumb. The guidance, "about 1 hour before loading preheat your oven and baking stone..." may or may not be quite enough. My oven, with the stone in, takes 40 mins. to reach 500°F.

David G

wayne on FLUKE's picture
wayne on FLUKE

Good info, thanks. I have the 15x20 Fibrament stone. Is that what you have also?

wayne

davidg618's picture
davidg618

Hi, Wayne,

I had them cut 3/4" off, so mine is 14-1/4" x 20"--otherwise, I'd have had to replace the glass everytime I closed the door;-)

David G

Yerffej's picture
Yerffej

David,

Your valuable information fits with my experience that, generally speaking, stones take at least an hour to heat up and even longer when dealing with very thick stones in commercial ovens.

Jeff

unrisen's picture
unrisen

Thanks very much, very helpful. I've given up with my stone as its not getting a nice crisp bottom, obviously its just not hot enough. Thanks again I'll give it another go.

breadman_nz's picture
breadman_nz

Fibrament takes a long time to heat and has a fairly sluggish thermal transer rate (which is OK for bread, but not so good for fast-bake pizza).

Another option to consider in home ovens is cordierite or the other alumina stones (I have a 16"x16"x3/4" sillimanite kiln shelf).

When I do pizzas, with a 1/2" steel plate on the top shelf (providing broiler function) and the sillimanite stone to bake on, the oven takes around 2 hours to heat up properly.

kmrice's picture
kmrice

after baking a pizza? 2 hour preheat is a long time, but I think it would be worth it if the stone then stays charged.

Karl

Yerffej's picture
Yerffej

Recovery time is a function of oven burner size (whether gas or electric) and the thickness of the stone.  Thinner stones in a home oven may need 20 minutes or more to fully recover.  Very thick stones in a deck oven will require little or no time to recover.

Jeff

breadman_nz's picture
breadman_nz

The stone stays well charged once hot... no worries about cool down time, and it's a 3-4 minute bake for a good NY-style pie.

warrax's picture
warrax

David,  on the Forno Bravo site, there is this tab with information about heating the stone:

wwwfornobravo(dot)com/pizza-stone/pizza-stone-performance.html

Forno Bravo is just rebranded Fibrament-D stone. It should be opposite, as you measured, as they claim, that their stone will heat up faster, than regular stone. So, you think, it is just advertisement?

davidg618's picture
davidg618

...except what is said about them by themselves, and customer's testimonies. They seem to have a quality product.

I looked at the pizza stone heating comparison. The data posted for the Forno-Bravo stone are in line with my experience with my oven, and my Fiberment stone. 

For what it's worth, if I were marketing Forn0-Bravo products I'd use testimonials and comparisons that favored Forno-Bravo too.

David G

varda's picture
varda

David, I preheat my oven for at least 40 minutes when I am using my stone which is a one foot square, one inch thick slab of Finnish granite.    If less than that the base of the  bread doesn't cook right.   If that or more, all's good.    My oven lists itself as preheated in 20 minutes or less depending on temperature.    If I'm in a bind, that is bread is proofed too early, I have learned it's better to get rid of the stone than use it too early.  -Varda

warrax's picture
warrax

I've checked granite thermal conductivity, and it is marked in the range of 2.9 - 4.0.

Fibrament stone thermal conductivity value is cca 1.7

Does it mean, that granite will store thermal mass in itself faster, than same sized block of fibrament stone?

 

Elagins's picture
Elagins

There's a really good technical comparison of the two materials here: http://www.pizzamaking.com/forum/index.php?topic=5645.0

Stan Ginsberg
www.nybakers.com

warrax's picture
warrax

Yeah, I've already read it, but it's not a granite. Cause I have an option to buy granite block 35x35x3 from stonemason. But it weights 10kg, so I think, it's too much mass. But if it have 2x higher thermal conductivity than fibrament (which weights about 5 kg same dimensions, so 1/2 of granite block), maybe it will pre-heat at same speed, as fibrament.

But maybe here comes into play another factor, which I don't know. Fibrament is thinner. Granite is more thick. I wonder, if granite can store more energy in itself, but it will give it away to dough more quickly. On Fibrament site in FAQ is mentioned, that exactly this factor is most important, except enough thermal mass for even cooking. It is called heat transfer rate. I would agree about this. If it is too much heat from thermal mass distributed, then bottom of the dough start to be too crispy, while middle of the dough is just not enough hot, cause dough thermal conductivity is not high enough to get the heat there.

So, when I combine it, there are 3 factors, that are important:

-Enough thermal mass of the stone for even heat distribution

-Just such volume, that will pre-heat, which means accumulate enough thermal mass, in short time

-Right heat transfer rate, not too much heat distributed in short time, and not too low heat distributed.

From this, I would say, that too much thermal conductivity will never hit right heat transfer rate, although, it will make the stone to pre-heat faster. I wonder, if heat transfer rate is calculated from thermal conductivity and trapped energy inside the mass. Then, it would really means to solve equation, that have only one solution, where heat transfer rate is constant, and thermal mass is just set to the value, it is needed for dough. Dimensions are constants, so result is thickness of material with right heat transfer rate. On granite it will not work, if heat transfer rate is too high. Maybe for meat, other heat transfer rate is needed, than for dough.

Yerffej's picture
Yerffej

While I do not have first hand experience with granite, I have read of it cracking under thermal shock.

Jeff

varda's picture
varda

I think there are a lot of different varieties of granite.   I've been using this Finnish white stuff for 2 years in my gas oven, and as the floor of my WFO.   I got one crack in one of the blocks in the WFO two years ago, and I had to replace that stone.   But that could also have been due to weathering.    Regarding the thermal properties - don't know the theory.   Just know how to use it from experience.   -Varda