Cooking for Geeks: Real Science, Great Hacks, and Good Food (49 page)
Read Cooking for Geeks: Real Science, Great Hacks, and Good Food Online
Authors: Jeff Potter
Tags: #COOKING / Methods / General
Mechanical leaveners work by trapping air within a liquid — usually by whipping egg whites, egg yolks, or cream — or by generating steam from water present in the food.
Unlike biological or chemical leavening methods, which rely on the chemical makeup of the food to generate air, mechanical rising techniques rely on the physical properties of the food to hold air. Because of this, mechanical leaveners can’t just be added to a dish without considering the impact of the moisture or fat that they also add, which can throw off the ratios between ingredients such as flour and water or sugar and fats.
“Cream the butter and sugar” has nearly three million exact-phrase matches on Google, and plenty is written about the microscopic air bubbles that the sugar crystals drag through the butter when creamed. When you see a recipe call for creaming butter and sugar, use room-temperature butter — it needs to be plastic enough to hold on to the air bubbles but soft enough to be workable — and use an electric mixer to thoroughly combine the ingredients until you have a light, creamy texture.
Whisked egg whites are the Styrofoam of the culinary world: besides acting as space fillers in cakes, waffles, and soufflés and as “insulators” in desserts like lemon meringue pie, when overcooked, they taste about the same as Styrofoam, too. All metaphors aside though, egg whites are much more forgiving than many cooks realize. With a little attention spent on understanding the chemistry and a bit of experimentation, egg-white foams are easy to master.
A foam is a mixture of a solid or liquid surrounding a
dispersion
of gas; that is, the gas (usually air) is dispersed through the liquid or solid, not in a single big cavity. Bread is a solid foam; whipped egg whites are a liquid foam. (See
Colloids
in
Chapter 6
for a description of colloids.)
The key to understanding egg whites is to understand how foams themselves work. Whisking egg whites turns them into a light, airy foam by trapping air bubbles in a mesh of denatured proteins. Since regions of the proteins that make up egg whites are
hydrophobic
— literally, water-fearing — they normally curl up and form tight little balls to avoid interacting with the water. But when whisked, those regions of the proteins are slammed against air bubbles
and unfold, and as more and more proteins are knocked against an air bubble, they form a layer around the bubble and essentially trap it in the liquid, creating a foam that’s stable.
Oils — especially from egg yolks or any trace oils present in the whisking bowl — prevent egg whites from being whisked into a foam because they’re also able to interact with the hydrophobic sections of the proteins. Water and sugar don’t interfere with the formation of protein-based foams for the same reason.
Once the air bubbles are encapsulated by the proteins in the egg white, it takes quite a bit of effort to get them to break. Exposing the whites to any oil before whisking is a problem; even a trace amount of fat from a small amount of stray egg yolk will interfere with the creation of the foam. But once the eggs are whisked, they’re much more resilient. Try this experiment: whisk an egg white to soft peaks, then add ½ teaspoon (5g) olive oil and continue to whisk. It might surprise you how long it takes before the oil starts to noticeably interact with the foam, and even then, that the foam remains mostly stable.
Definitely not plastic. Copper bowls work best; a clean stainless steel or glass bowl is fine.
Plastic is chemically similar enough to oil that oil molecules stick around on it and are impossible to completely remove. Whisking egg whites in plastic bowls doesn’t produce as good a result because there’s enough oil lingering on the surface of the bowl to interfere with the development of the foam. (Of course, it’s fine to whip cream in a plastic bowl; more fat isn’t going to interfere with the fat-based foam structure.)
When you use a copper bowl, trace amounts of copper ions interact with the proteins in the egg whites to make a more stable foam. It’s not a subtle effect: egg whites whisked in copper bowls are definitely easier to work with. Copper bowls are expensive, but if you find you’re whipping up egg whites a lot, it’s probably worth breaking down and spending $40 on one.
For more occasional use, most of us have stainless steel or glass bowls on hand, and those are fine. While these materials won’t help with the egg-white foam by adding copper ions, they also won’t hold on to problematic fats. Cream of tartar is commonly used as a chemical buffer — any time you see a recipe calling for egg whites to be whisked and you’re using stainless steel or glass, “auto-complete” it with a pinch of cream of tartar (⅛ teaspoon [½ g] per egg white). Don’t use cream of tartar in a copper bowl, though; it’ll interact with the copper.
Try an experiment: whisk three whites in a plastic bowl, three whites in a stainless steel or glass bowl, and, if you should happen to have a copper bowl, three whites in a copper bowl. Take a spoonful of the resulting foams and smear it on a cookie sheet to compare the difference between the foams.
Egg whites whisked to stiff peak in a stainless steel bowl (left) and a copper bowl (right), smeared on a cookie sheet to show the difference in texture.
Egg whites, when whisked and combined with sugar, turn into a sweet, airy mixture suitable for folding into heavier bases, bringing a lightness and sweetness. Of course, sugar and egg whites are pretty good on their own — meringue cookies are nothing more than egg whites and sugar that have spent a little time in the oven. The sugar isn’t just for taste, though; it helps stabilize the egg-white foam by increasing the viscosity of the water present in the foam, meaning that the cell walls in the foam remain thicker and are thus less likely to collapse. Net result? The meringue is better able to support the weight of anything you add into the foam.
When whisking, think about the goal. If you’re trying to whisk air into the food to create a foam, such as whipped cream or whipped egg whites, whisk — preferably by hand! — in an up-and-down circular motion, catching and trapping air. If you’re trying to mix ingredients together without necessarily adding air, whisk in a flat circular motion. This is especially important for dishes like scrambled eggs, where incorporating air actually reduces the quality.
I prefer whisking things by hand. Why? Electric beaters won’t work in as much air before the foam is set because of the motion of the beaters. Also, when whisking, avoid tiny little stirring motions. This is true for stirring almost anything, whether you’re holding a whisk or a spoon. Sautéing vegetables? Either get in there like you mean it, or don’t touch them; just let them sit so that they brown. Likewise, when whisking foams, get in there like you mean it and whisk some air in there!
Once you’ve got the motion down, how do you know when it’s done? It depends on the recipe. If it calls for soft peaks, the foam should still be supple and pliable, but if it calls for firm or stiff peaks, the foam should hold and set its shape; stiff peaks should be firmer and glossier than firm peaks. (See
Making Whipped Cream
in
Chapter 1
for more photographs of cream whipped to various states.)
When it comes to folding egg whites into a batter, as long as you’re using a whisk or spatula — not an electric mixer — you can be a bit more vigorous than conventional wisdom suggests.
Soft peak stage: the foam stays on the whisk but the peak falls over.
Firm and stiff peak stages: the foam maintains its shape and can be sculpted.
There are two general forms of meringues: those in which the sugar is directly added as the egg whites are whisked (French Meringue), and those in which the sugar is dissolved before the egg whites are whisked (Swiss and Italian Meringue — we’ll cover Italian here, but they’re similar). The French version tends to be drier (sugar is hydroscopic, sucking the moisture out of the whites — this is why it increases viscosity) and also grittier; the Italian version has a smoother, almost creamy texture.
French Meringue
In a clean bowl, whisk 3 egg whites to soft peak stage.
Add ¾ cup (150g) of sugar — preferably super-fine sugar — one tablespoon at a time, while continuously whisking. If using regular sugar, you’ll need to whisk longer to make sure the sugar is entirely dissolved. To check, roll a little bit of the meringue between two fingers (it shouldn’t feel gritty).
Italian Meringue
Create a simple syrup by heating in a saucepan ½ cup (100g) sugar and ¼ cup (60g) water to 240°F / 115°C. Set aside.
In a clean bowl, whisk 3 egg whites to soft peak stage. Slowly pour in sugar syrup while whisking continuously.
To make meringue cookies, start with either egg-white meringue recipe. Optionally fold into the meringue whatever ingredients you’d like — ground almonds, chocolate chips, dried fruit, cocoa powder.
Using a spoon or piping bag, portion the meringue onto a cookie sheet lined with parchment paper. Bake in an oven preheated to 200°F / 95°C for a few hours, until they freely come off the parchment paper.
No piping bag? No problem. Put your filling in a large resealable bag and snip off one of the corners. You can use Italian meringue as a topping on desserts as well.
For more on meringues, see
Savory French Meringues
in
Chapter 6
.
One of the great things about this chocolate port cake — besides the chocolate and the port — is the recipe’s wide error tolerances. Most foam cakes — those cakes that rely on a foam to provide the air — are very light (think angel food cake). The reason this recipe is so forgiving is that it uses a foam without trying to achieve the same lightness.
You’ll need a small saucepan, two clean bowls, a whisk, and a round baking pan or springform pan, 6–8” / 15–20 cm.
In the saucepan (over a burner set to low heat), melt and mix together, but do not boil:
- ½ cup (125g) port (either tawny or ruby)
- ½ cup (114g) butter
Once butter is melted, turn off heat, remove pan from burner, and add:
- 3 oz (85g) bittersweet chocolate, chopped into small pieces to facilitate melting
Leave the chocolate to melt in the port/butter mixture.
In two bowls, separate:
- 4 large (240g) eggs
Make sure to use a clean glass or metal bowl for the egg whites, and be careful not to get any egg yolk into the whites.
Whisk the egg whites to stiff peaks.
In the bowl with the egg yolks, add:
- 1 cup (195g) granulated sugar
Whisk the egg yolks and sugar together until thoroughly combined. The yolks and sugar should become a slightly lighter yellow after whisking for a minute or so. Pour the chocolate mixture into the egg yolk/sugar mixture and whisk to thoroughly combine.
Using a flat wooden spoon or flat spatula, add to the chocolate mixture and fold in (but do not overstir!):
- ¾ cup (100g) all-purpose flour
Then fold in the egg whites in thirds. That is, transfer about a third of the whisked egg whites into the chocolate mixture, mix together, and then repeat twice more. Don’t worry about getting the whites perfectly incorporated, although the batter should be relatively well mixed together.
Grease your cake pan with butter and line the bottom with parchment paper, so as to make removing the cake from the pan easier. Transfer the mix to the cake pan and bake in an oven preheated to 350°F / 175°C until a toothpick or knife, when poked into the center, comes out clean, around 30 minutes.
Let cool for at least 10 to 15 minutes, until the edges have pulled away from the sides, then remove from pan. Dust with powdered sugar (you can use a strainer for this: place a few spoonfuls of powdered sugar in the strainer and then jog it with your hand above the cake).
Note
- When working with chocolate in baking, don’t just substitute, say, 80% bittersweet chocolate for a semisweet bar. In addition to differences in sugar, the two types of chocolate have different quantities of cocoa fat, and recipes that rely on the fat level will need to be adjusted accordingly.
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If you grew up with a brother or sister, you’re undoubtedly familiar with the technique for avoiding fights when splitting food: one person divides it, and the other person chooses. (“You can halve your cake, and eat it, too!”) But what to do if you have more than one brother or sister?
There is a solution, but it’s a bit more involved. Here’s the algorithm for cutting a round cake for
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people. It’s not perfect — don’t use this for negotiating land divisions after minor land wars — but when it comes to a table of kids and a large chocolate cake, it’ll probably work. (If you find yourself cutting cake for hardcore math geeks, however, I suggest reading up on the literature. Start with An Envy-Free Cake Division Protocol —
http://www.jstor.org/pss/2974850
— and plan to be at it for a while.)
Only one person actually does any cake-cutting, and that person can either be a cake-eater or just a referee. Start with the cake in front of you, along with a knife and
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plates. Proceed as follows:
- Make a first cut in the cake, as normal.
- Explain that you’re going to slowly hover the knife above the cake while moving it clockwise around the cake, just like someone thinking about how big the next slice should be. Anyone — including the person cutting the cake — can say “stop” at any point to declare that they want a piece that size, at which point, that’s where you’ll cut the next slice.
- Slowly move the knife above the cake until someone calls stop.
- Slice the cake and hand the person who called stop the new slice. Continue with step 3 with the remaining cake eaters. (To be clear, anyone who calls “stop” is now out of the negotiation and doesn’t get to call it again.)
- When you’re down to just one last person, cut the cake wherever he or she likes, which may leave a leftover piece.
One of the nice things about this protocol (a protocol is similar to an algorithm, but allows for accepting user input after being started) is that it allows people who for whatever crazy reason want small slices to do so, and gets them out of the way at the beginning, meaning if somebody else wants a larger slice than an equal
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division would allow, they get more cake and can eat it, too.
If someone is being greedy and wants a too-big piece, they’ll end up getting the last slice — which will normally be the largest slice. If two or more people end up being greedy, though, they could allow the referee to reach the end of the cake by never calling stop, in which case I suggest eating the cake yourself. There’s no guarantee that this protocol will satisfy everyone — just that the honest actors are protected from the dishonest ones.
