On National Cheese Pizza Day, we look back at an instructive article from Bob McDougall.
If there’s one particular thing that every pizzaiolo stresses over, and every customer has at least one opinion on, it’s cheese colour. Not what the cheese looks like on the make table, but on a baked, finished pie.
Let’s examine some factors in the interaction of cheese and the oven. It won’t solve the question of the ages – what cooked cheese colour is best – but it may help to understand how to get any particular target colour without under- or overcooking the pizza.
Consider if you will, the two most common oven types. One cooks by providing heat from a base in direct contact with the pie or its pan, and heat radiation from surfaces (deck or traditional oven). The other predominantly uses moving hot air to transfer heat into the pie (conveyor or forced air convection ovens).
In Canada, many great pizzas are sold from each oven type. There isn’t a clear winner. Each has merits and disadvantages. That being said, there are still many discussions, harangues and long-standing grudges about which is “best.” Let’s examine what each will do to a pizza.
The deck oven receives a pizza in most cases directly upon its cooking surface. In those cases where a pan is used, most of the following applies, although the situation is influenced by the pan’s modification of heat flow.
The “mass” of the oven’s cooking surface (whether stone, steel, brick or whatever) is large, and holds a lot of heat. That heat very quickly moves into the pie through the crust, pushing moisture from the crust upwards. The hot moisture or steam carries heat up through the sauce layer, in turn heating it to its boiling point. All this moist heat then moves on to the toppings and cheese layers. This provides softening and hydration to cheese and leading typically to a soft and lasting melt from even the lower moisture or overly firm mozzarellas, which have predominated in some segments of the market over the last several years.
Browning and burning is often minimal, and is largely a result of radiated waves of infrared heat from oven walls. This heat acts essentially at the surface of the pie, and does not penetrate to any great depth. The cook comes from the bottom. Moisture does leave the pie, but does so more slowly than if a hot wind was present to desiccate the surface. These are the properties that lead to excellent cooking abilities for thin crusts, traditional dryer crusts and toppings easily dried out and burnt, such as broccoli, bacon bits, sprigs of herbs such as rosemary and the like.
In order to properly bake thicker crusts in a deck, wetter components must be avoided. Raw tomatoes are problematic, as are watery sauces or wet cheeses like poorly drained ricotta. Remember, the thicker the crust, the slower the transfer of heat described above. Using lower temperatures for longer times can help, as can the use of perforated or dimpled pans and even heat pins for “deep-dish” pies. More temperature will give you more colour or browning, and up to a certain point will help with speed of bake.
The most important contributor to a better-baked pie is still more time.
On the flip side, convection ovens provide heat to the pie from air. This heat transfer is inherently less efficient due to the “nature of heat flow between media of different thermal characters” – in other words, you can get more heat faster from a stone/metal surface than from hot air. Except maybe in Ottawa, just about now.
The heat moving into the pie comes in from all sides. It may not, however, enter equally. Heat is slower to arrive through a pan, but once it is moving into the pie, it is more uniform and continues even after the pan exits the oven. Heat from the top is quick to enter, and its effect extends deeper than the radiated heat from a deck oven, but like the heat from a deck, it essentially stops immediately upon oven exit. As a result there is no single main directional movement of heat and moisture.
There is, however, a huge loss of water from any exposed surface due to the hot wind. Consequently, cheese on such a pie needs to better resist drying and burning. As a result, a higher moisture and less stiff mozz typically performs better in such an oven. A higher quality mozz, by which I mean one with a lesser tendency to release butter fat (oiling out), will also help to prevent burning problems. Free oil on a pizza tends to keep the surface hotter, leading to darkening. Many believe this to be a result of preventing evaporation from the surface.
Hang on – isn’t preventing evaporation good? Well, yes, but no. Evaporation can lead to drying, but (as we all know from the cooling effect of a breeze on a hot, sweaty day) it also reduces surface temperature. This evaporative cooling can keep the top of a pie tens of degrees cooler than it would otherwise be. This is what is seen with a heavy layer of fresh veggies on a pie. The cheese is whiter and often more moist immediately around the veggie pieces, as a result of the localized cooling. A key, then, to getting just the right colour to the top of a pie is to “tune” the amount of moisture in the top layers and its proximity or exposure to the hot wind. Think carefully of your build order!
The presence of a pan of course prevents any evaporation, although water is released through boil-out. This means sogginess is reduced by using lower moisture items in the pan or lower down in the pie, where it is out of exposure to the drying, hot air.
As for the deck oven, a fully-cooked pie is largely the result of adequate time for enough heat to enter the pie to set and cook all parts. More temperature will give you more browning, and to a certain point will increase the speed of heat entry in the first, or pan heating part of the cook. It will not typically cook the pie any better. The balance between temp and time is more involved than with a deck oven, and typically leads to the determination of a “best” temperature as much as 100F degrees lower than a traditional Italian-style deck for some products. Even with this lower temp, since there is no dependence upon heat moving in from only one source direction, times can be faster.
The overall result is that a convection oven can bake pizzas that are nearly impossible to do well in a deck oven, and can often do things faster. However, a deck can definitely bake great pizzas that are nearly impossible in a conveyor-style convection oven. Both can provide a beautifully baked and browned pizza, with the cheese just as you like it. However, you may need to be very careful in selecting your cheese, toppings and in how you build your pies.
The science of food is exciting and interesting. The art of pizza is delicious and satisfying. The fun, at least for me, comes from using the first to improve and serve the second.
Bob McDougall is a microbiologist, with postgraduate training in biochemistry and food science. He has held senior operations, quality and product innovation roles in meat, dairy and other sectors, and is a veteran of the pizza wars of the last decade of the second millennium. For seven years, Bob managed all quality, R&D and technical services for the Canada division of the world’s largest pizza chain. He is currently principal consultant with RJMA (The Food Technical Consultancy) and Consulting Senior Food Scientist for the Food Innovation Research Studio at George Brown College.
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