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The Pizza Lab: On Flour Types, Foams, and Dough
It's time for another round of The Food Lab. Got a suggestion for an upcoming topic? Email Kenji here, and he'll do his best to answer your queries in a future post. Become a fan of The Food Lab on Facebook for play-by-plays on future kitchen tests and recipe experiments.
Pop quiz: What do whipped cream, Nerf footballs, pizza, and Tempur-Pedic mattresses have in common? That's right — they're all foams.
Wait, huh? Pizzas are foams? You mean those annoying, piddly things that chefs were goofing around with in the mid 2000s? Yup, as are hot dog buns, Wonderbread, Pane di Genzano, Portuguese rolls, Naan, pancakes, and pretty much every other leavened batter or dough-based product in the world.
Why do I bring this up now? Well, it's not quite obvious, but once you start thinking of bread as a solid foam, it becomes much, much easier to understand its mechanics; how leavening works, what gluten development is, oven spring, and the like. Today, we're going to discuss a subject that we've danced around a few times in the past (like when we were exploring how to make Neapolitan-style pizza at home even without a wood-burning 1000°F oven), but have never really explored in detail.
Now for you professional bakers and pizzafreaks out there, after today you'll probably still feel like we haven't really explored the subject in detail, but flour is a gigantic can of worms that only gets deeper and deeper, and for most of us, a good understanding of the very top layer is good enough for our needs.
First off, what exactly is a foam? At its most basic, it's a collection of many air or gas-filled bubbles accumulated into a single larger mass.
Fluid foams, such as shaving cream, a whipped meringue, sea scum, or the head on your beer is made of bubbles surrounded by a viscous liquid. The bubbles can slip and slide past each other, giving the entire mass mobility and shape-ability. But here's the interesting part. Depending on the viscosity and surface tension of the liquid, the strength of the individual bubbles in a foam can vary greatly. Plain water can hold a few tiny bubbles for a brief period of time on its surface. Thicken that water up or change the characteristics of its bonding with, say, some soap, and you can suddenly form much larger bubbles with sturdier structure.
Bubble size can also vary greatly depending on how the bubbles are formed. Though their size is limited by the strength of the bonds between individual liquid molecules, the mechanical means by which they are formed can change their size dramatically. Agitate a bubble bath slowly, or blow through a soapy film and you can create very large bubbles. Vigorously shake that exact same solution or better yet, throw it into a blender or beat it with a mixer, and you can create very fine bubbles indeed.
But again, what's this all got to do with bread?
Bread = Solid Foam
Turns out that bread is a solid foam — that is, a foam that's been treated after it's formed to solidify its walls and firm up its structure (ever look inside a sliced loaf of bread and wonder why it looks so much like the top of a bubble bath?). And just like with soapy water vs. plain water, the exact makeup of the walls of these bubbles and the way in which they are formed can affect their size and strength. Without bubbles, bread would be a solid brick of protein and starch, much like, say, a dog biscuit. It's the inclusion of bubbles of gas that make bread tender, chewy, and, well, edible.
While there are a number of factors that can affect bubble characteristics in bread foams, the overriding factor by far is the type of flour your use, and more specifically, its protein content.
Wheat flour, the ground up grain of the wheat plant, is composed largely of absorptive, sticky starch molecules, along with a few protein molecules, most importantly the molecules gliadin and glutenin. It's these molecules that cross-link with each other in the presence of water, forming the strong, elastic matrix known as gluten. Gluten is like soap for your dough. The more gluten is formed, the easier it is to form large, robust, stretchy bubbles in your loaf. Thus, just like adding more Mr. Bubble will make your bubble bath foamier, the more protein in your flour, the larger and more robust the bubbles you can form in your dough.
Okay, okay. There are other factors that can affect your flour performance as well. Check out this article for a more thorough rundown of wheat varieties.
Dough for bread in which you want very large bubbles (like pizza!) should be reinforced with enough gluten that you can stretch it out thin enough to see through (this is known as the "windowpane" test). In order to form this tough matrix, dough must be kneaded until the proteins link up with each other strongly,* and as we've seen in the past, the food processor is the best way to rapidly develop gluten in your dough.
*there are exceptions to this rule, such as with no-knead style doughs, in which the dough is simply allowed to sit out overnight. Through a combination of autolysis, plenty of water, and the action of yeast bubble production, the dough essentially kneads itself, forming gluten with almost no outside help.
When it comes to pizza, there are a number of options. Let's take a look at some of them.
The Major Types of Flour
Believing that the experts of the world will ever agree on what makes the best pizza dough is as crazy as thinking that Wilykit and Wilykat will give up their mischievous ways, but there are certainly a few things we can all agree upon when it comes to Neapolitan pizza crust.
Captuo "00" Bread Flour
Protein Content: 12.5%
Water Absorption: low
This is the gold standard of pizza flours by which most others are judged, but there's quite a bit of confusion as to exactly what it is. You'll read in countless sources that Italian Tipo "00" flour, like the Caputo, is a "soft wheat flour," with a low protein content. This is absolutely untrue and anybody who continues to spread this rumor should be immediately chastised with great prejudice.
The fact is, the label Tipo "00" has nothing to do with protein content. Rather, it refers to the fineness of the milling. Tipo "00" is the finest grade of flour milled in Italy, and it has a consistency similar to baby powder. It's available with several different levels of protein intended for different baking projects, just like American flours (which we'll get to in a moment). The ones you'll most commonly see in pizzerias are the red Rinforzato bag, which features pictures of pizzas and bread, the blue Pizzeria bag, which pictures a single pizza, and — the most common in the U.S. — the red The Chef's Flour bags, which, in fact, contain the exact same flour as the Rinforzato. All three bags of flour have the exact same protein content: 12.5%
Because of the fineness of their milling, they don't need quite as much water as an equivalent American flour (try making a 65% hydrated dough with "00" and American bread flour side-by-side and you'll find that the "00" is much runnier).
So what's the difference between the Rinforzato and the Pizzeria? Caputo guards that secret very closely, though one could assume it has to do with the blend of wheats that make it into the bag. As far as baking with them goes, I've not noticed a huge difference between the red and blue bags—both produce admirably workable doughs that produce great crust with a crackly-thin layer of crispness, a nice open and airy hole structure, and just a modicum of chew. I stick with the red bag, because it's easiest to find (Whole Foods carries it, and you can order it in 10 kilogram packs from Amazon.
Most Neapolitan pizza dough recipes you see around here attempt to come up with viable substitutes for Caputo "00." None of them really work precisely. Do yourself a favor and order it online.
Protein Content: 11.7%
Water Absorption: moderate
King Arthur all-purpose flour has a slightly higher protein content than most other brands, which clock in at around 10.5 to 11%. All-purpose flour is exactly what it sounds like. With a moderate protein content, it's does a decent job at a wide range of goods from pizza and bread to cakes and biscuits. However, it doesn't excel at any of them.
As you can see, bubble development is limited, giving you a network of relatively small bubbles instead of the large, irregular structure you get with the "00". With cakes and pastry, you'll have the opposite problem; biscuits come out a little tougher than you'd like, and cakes with a distinct chewiness. If there's only one flour you keep in your pantry, this should be the one, but if you've got the space, you might want to consider a few specialized flours.
Protein Content: 12.7%
Water Absorption: high
American bread flour has a protein content similar to that of the Caputo bread flower (King Arthur's actually gets a little bit higher even). The main difference in how it behaves is due to the exact type of wheat used and the grind size—American bread flour produces stretchier, chewier breads than Italian "00" bread flour. Whether or not this is a good thing is totally up to user preference.
As you can see, the foam structure bread flour produces is significantly more robust and irregular than that of all-purpose flour. Similarly, it's also stretchier and chewier. For Neapolitan pizza, this means that you're going to end up with a taller cornicione, and better protection against sagging out with sauce and watery cheese. Will it produce a traditional Neapolitan pizza with a super-crisp, airy, and delicate crust? No. But the pizza it does produce is great for its own merits.
Bread flour requires a little more water than most other flours to produce doughs of equivalent viscosity. Because of its high protein content, some people may find bread flour doughs a little difficult to stretch — it has a tendency to bounce back. The key is to make sure that it's well-rested before you being to stretch it.
Side Note: do not try to bake a cake using bread flour.
Cake or Pastry Flour
Protein Content: 9.4%
Water Absorption: low
Of all the types of flour, Cake is the one that produces doughs and batters that are most obviously foam-like, with many small, delicate, tightly packed bubbles. It's what gives cakes and biscuits their dense yet delicate texture. Because of the misconception that "00" flour is a low-protein flour, many people recommend using some proportion of cake or pastry flour in their pizza dough. While this will indeed produce a softer finished product with a thinner, crisper crust around a tender center, you run into a few problems. check this out:
While there are a few large bubbles in the cornicione, these bubbles are not formed by stretching out a small bubble into a large bubble the way they are formed with high-protein flour doughs. Rather, those bubbles are formed when many smaller bubbles collapse and break into each other, due to their weak structure. The results is a crumb structure that is not so much chewy or stretchy as it is tender.
The other, even bigger problem is underneath the sauce and the cheese. As you can see, the dough gets mushed down and compressed to an almost paste-like state. The walls of the individual bubbles are simply not strong enough to support any kind of weight on top of them. What should be light and airy instead loses steam (quite literally), becoming dense and gummy.
Save the cake flour for the cake!
King Arthur "Italian Style" Flour>
Protein Content: 8.5%
Water Absorption: low
A couple of years ago, King Arthur came out with what they call a "00" clone, intended to be a competitor to the Italian brands. Frankly, it's no competition. For some baffling reason, they decided to use an even lower protein content than their normal pastry flour, resulting in doughs that bake up ultra-tender and crisp— good things — but with no chew and a very easily-collapsable structure — bad things.
I've still yet to see a completely acceptable substitute for Italian flour.
So What's It All Mean?
Well, as I said, this is hardly a complete guide to flour. We haven't even touched on bleaching, bromating, whole grain vs. refined, differences between brands, not to mention other factors that affect dough like yeast, water content, and mixing, all of which can make profound differences on your finished product.
Pizza dough is as personal as topping choices — even more so in fact. Ask any two pizza-makers, whether they be home pizzafreaks or professional pizzaioli and you'll get two different recommendations for which flours to use. Having an understanding of how flour works and what different types of flours are out there is a very valuable first step towards coming up with your own ideal blend, but the real key with finding a dough that works for you is to just jump in and get your hands dirty.
And the next time you shave, toss the football around, or hop in the bubble bath, think about your dough. You'll be a richer, wiser, better-fed person for it.