Episode 1 - Do pizza stones absorb moisture from a pizza while it bakes?Like the claim that NYC water makes better pizza, say something enough and people will believe it. Say it a few more times, and they will refuse to listen to anything to the contrary. To this end, there is no shortage of people who believe pizza stones absorb moisture from the pizza as it bakes. It's hardly surprising, a quick Google search turns up dozens, if not hundreds of websites that all say something to the effect:
"Pizza stones are made of porous materials to absorb moisture easily." (
http://www.foodservicewarehouse.com/education/how-to-use-a-pizza-stone/c31723.aspx#sthash.w7cgmKKE.dpuf) Even Wikipedia, the poster child for 'you can't put it on the internet if it isn't true' gets in on the action. Seven websites promoting the myth are listed here:
http://www.pizzamaking.com/forum/index.php?topic=28243.msg379789#msg379789.
Manufacturer,s such Breville for example, use the myth to try to sell product:
"The pizza stone's porous surface absorbs moisture from the pizza dough, resulting in a crisp brown pizza crust." (
http://www.brevilleusa.com/13-pizza-stone.html). This site that purports to be a pizza stone buying guide and namer of the best pizza stone for 2015 talks about a pizza stone absorbing moisture four times:
http://thoroughlyreviewed.com/home-kitchen/pizza-stone-review/Of everything I read this afternoon however, I found this bit on Serious Eats to be the most interesting:
"The point of using stone or ceramic instead of metal is that the stone absorbs moisture from the dough, resulting in a crisper crust. So, glazing sounds like a bad idea, right? According to packaging description, the glaze is "micro-crazed" which sounds a lot like my mental health some days, but it actually means that the glaze has teeny cracks, so the stone can still absorb moisture." http://slice.seriouseats.com/archives/2011/04/pizza-protips-baking-surfaces-part-6-emile-henry-pizza-stone-review.html
Perhaps at the time, it said this on the Emile Henry Website, but it doesn't today,
"The glaze is micro-crazed contributing to crispy well-baked crusts, just like a pizza oven." I don't see anything about absorbing moisture. It would seem that the Serious Eats author is so programmed to believe the myth that she automatically assumed this is what the manufacturer was talking about (maybe they were) and then proceeds to imagine and explain how it works!
So what is the truth? Does a pizza stone absorb moisture as the pizza bakes? Common sense seems to suggest NO. At one atmosphere, the density of steam is about 0.6kg/m^3 or 0.006g/cm^3. Say you have a typical decent stone (0.5" x 16" x 14"), that would be 1,835cm^3. The mass of steam/water at normal operating temps that could occupy that volume if there was NO stone is 1.1g. Now consider that probably 99+% of the volume is stone and assume there is 1% open space, if it was fully saturated, the stone could hold 0.11g water. That's the MAXIMUM possible; I'd guess that the water absorbed from a pizza by the stone is meaningfully less than 0.01g.
Simple physics also seem to suggest NO. The Ideal Gas law Tells us that PV=nRT (the letters represent Pressure, Volume, amount (in moles), ideal gas constant, and Temperature of the gas, respectively). In simple terms, as temperature increases, if there is nothing to contain the gas, pressure will remain more or less constant and volume will increase - or vice versa at a constant volume. Let's say some steam or water vapor enters the stone from the pizza; unless the stone is cooler than the pizza, the temperature of the steam/water vapor will increase. Since there is nothing containing the steam on the top side of the stone, the volume of steam will increase and pressure will remain more or less constant. The net effect is that most water that enters the stone will be forced OUT.
I also did a couple experiments to test if the theory is supported by real world observations. My pizza stone is to heavy for my scale to weight with 0.1g precision, so I took a solid brick with a pore structure that looked similar to, if not a bit more open than my pizza stone, and broke it in half. I weighed both halves and then put one half in the oven at 475F for an hour and submerged the other in a sink full of water. The piece in the sink gained about 5.7g while the piece in the oven LOST 41.1g. There was some moisture in the brick, and it was forced out as the temperature increased exactly as the theory predicted. If moisture in the stone is being forced out, what are the chances it is going to absorb moisture from a pizza? At this point, I was pretty sure thee myth was dead, but I pushed on.
In the next test, I placed 5ml (5g) water on the stone, closed the oven door, waited 30 seconds, then weighed the stone. It gained 0.1g that dissapeared within the next 30 seconds. I then put another 5ml water on the stone and placed two corn tortillas right on top of the water to try to trap some in the stone. Again I waited 30 seconds and weighed the stone. Like the first test, it gained 0.1g that dissipated in the following 30 seconds.
Lastly, I made a simple 65% dough from flour and water only and baked a small pizza analogue (80g, 5", TF=0.14) for 7 minutes. The stone actually lost 1.4g in the process. Not only did it not absorb any moisture, it forced more previously trapped moisture out just as I would expect from the theory. For the final test, I put 5ml water on the stone and baked another pizza on top of it for 8 minutes. The stone gained 0.1g, however the pizza stuck badly to the wet stone, and some, if not all, the additional weight was crust stuck to the brick.
Bottom line, there is nothing - not common sense, not theory, and not experimental results - supporting this myth being true.
This myth is