Colloids: Gels

Similar to our previously mentioned foams, the gels we made today are a type of colloid.  They occur when a solid is dispersed within a liquid.  We used gelatin as our basic gelling agent, a tricky convenience because gelatin is lyophilic.  This means it can be made easily by simply warming the substances, so we could use the same base and ingredients to make multiple different types of gels.  Adding differing amounts of gelatin was what allowed us to make different textured gels- candy-like gummies, jelly, and a jell-o somewhere in between the two.

We began by making a fruit base as the flavoring for our gels.  We blended up some berries, sugar, juice, and corn syrup to make a deliciously sweet concoction.

We then separated the syrupy flavoring into three 1/3 cup measures, one for each type of gel we intended to make.  Each was heated to a boil, at which point the corresponding amount of gelatin was added.  Incidentally, the gelatin had to be sprinkled evenly over the hot liquid to avoid clumps of unflavored gelatin granules in the final product.

A brief explanation of what happened at this point of the cooking process: The gelatin began at room temperature, organized into a structure by intermolecular forces.  Upon heating, these forces were broken, allowing the gelatin to take in the water molecules.  As the gels cooled, the intermolecular forces were reinstated, but this time with the water molecules interspersed evenly.

We let the gels cool until they had reached room temperature, and the consistency we were searching for.  In the end, we had fruit gummies, fruit jelly, and real fruit jell-o.  So many gels, so little time...

Emulsions: Mayonnaise and Pasta Salad

An emulsion is a mixture of substances that would not otherwise be soluble with each other.  In middle school chemistry we learned that "like dissolves like," meaning that polar substances will only dissolve with other polar substances because the intermolecular dipole-dipole partial positive and negative charges will attract one another.  Likewise, nonpolar substances have no permanent partial charges, so they do not attract polar particles but do disperse within each other quite nicely.  However, when we mix a polar substance, such as water, with a nonpolar substance, like oil, we find it impossible to integrate the two.

Incidentally, polarity arises from the differing electronegativity of elements.  Electronegativity is the tendency of an atom to pull electrons towards itself.  The smaller the atoms, and the more protons it has, the more strongly it can attract electrons becuase the positive protons in the nucleus are closer to the electrons, and there are more of them to create a n attractive force.  Following this trend, the most electronegative elements (such as Flourine, Nitrogen, and Oxygen) are located in the upper right side of the periodic table.  When these elements are bonded with a very weakly electronegative atom, the result is a tendency of the electrons to congregate by the electronegative element, creating a partial negative charge at that end of the particle and a partial positive charge at the other end.  This is a polar substance. If the atoms have similar electronegativities, no such grouping exists and the substance is nonpolar.

So how do we mix polar and nonpolar substances into an emulsions?  The answer lies in emulsifiers.  These tricky little molecules have both a polar end and a nonpolar end, so that they can dissolve both polar and nonpolar substances.  Mayonnaise, a common emulsion, is made possible by the emulsifyer mustard.  This was the emulsion we chose to attempt.

Ingredients
1 egg yolk*1/2 teaspoon fine salt1/2 teaspoon dry mustard2 pinches sugar2 teaspoons fresh squeezed lemon juice1 tablespoon white wine vinegar1 cup oil, safflower or cornDirectionsIn a glass bowl, whisk together egg yolk and dry ingredients. Combine lemon juice and vinegar in a separate bowl then thoroughly whisk half into the yolk mixture. Start whisking briskly, then start adding the oil a few drops at a time until the liquid seems to thicken and lighten a bit, (which means you've got an emulsion on your hands). Once you reach that point you can relax your arm a little (but just a little) and increase the oil flow to a constant (albeit thin) stream. Once half of the oil is in add the rest of the lemon juice mixture.
Continue whisking until all of the oil is incorporated. Leave at room temperature for 1 to 2 hours then refrigerate for up to 1 week.
* Raw Egg Warning
Read more at: http://www.foodnetwork.com/recipes/alton-brown/mayonnaise-recipe/index.html?oc=linkback

Troubleshooting common emulsions:

Troubleshooting Emulsion Sauces When an emulsion breaks, how you fix it depends on the sauce.
	Problem	Cause	Fix
MAYONNAISE	The mayonnaise fails to thicken.	The oil has been added too quickly, so it never gets dispersed.	Beat a fresh egg yolk with a tablespoon of water and/or lemon juice in a clean bowl, and slowly whisk in the broken sauce.
	The mayonnaise becomes oily on the surface.	Water has evaporated from the mixture, giving the oil droplets a chance to coalesce.	Whisk in a spoonful of water.
HOLLANDAISE	The sauce is lumpy and thin.	The egg yolk has overcooked.	Strain out the lumps and whisk the hot broken sauce into another gently heated egg yolk in a clean bowl.
	The sauce has separated while being kept warm.	The sauce has become too hot, causing the butterfat to leak.	Take it off the heat and whisk it vigorously, or briefly re-emulsify it in a blender.
VINAIGRETTE	The oil and vinegar have separated.	The simplest vinaigrettes do not contain emulsifiers like mustard, so the oil and vinegar separate unless they are being actively mixed.	Whisk the broken vinaigrette in a bowl or shake it vigorously in a closed jar and pour it over the food immediately, while it's still in motion. A separated mustard vinaigrette is fixed in the same way.
BEURRE BLANC	The sauce hasn't thickened.	The ratio of butter to liquid is too low. Either the vinegar mixture was not reduced enough before the butter was added, or not enough butter was added.	Add more butter.
	The sauce is creamy at first, but then suddenly thins.	The sauce has become too hot.	Because all of the elements to maintain an emulsion are still present, all you need to do is remove the sauce from the heat and whisk in ice chips, a few at a time, until the emulsion returns.

Colloids: Foams

Light and airy but nevertheless decadent, chocolate mousse is a dessert worthy of its reputation.  Though it is somewhat finnicky, the result is completely worth the effort.  And with a little bit of knowledge about the chemistry behind this confection, it becomes very easy to whip up the perfect dessert.

To begin, a colloid occurs when one substance is microscopically dispersed in another substance.  To put it into perspective, colloids are the midpoint between a solution and a mixture.  This is generally occurs when particles dispersed are between 1 and 1000 nanometers large.  There are different types of colloids, depending on the states of matter of each component.  The type we created, a foam, occurs when a gas (air) is trapped in tiny bubbles in a liquid (egg whites).

To begin, we melted butter, coffee and chocolate together in a double boiled to create a ganache.  We then set this aside to cool while we prepared the eggs.

We separated the eggs, making sure not to let the whites come into contact with any fats.  This would have prevented the proteins from forming bubbles to their full potential.

We then added cream of tartar to the egg whites (as an acid, it stabilizes them so they can take on more volume) as well as salt and a bit of sugar.  Molly whipped them up into nice stiff peaks while I dealt with the yolks.

To the yolks I added sugar and a bit of water.  I stirred the mixture over a double boiler to dissolve the sugar and cook the eggs, and then transferred the bowl into a larger bowl of ice water for cooling.  As the temperature came down, I beat the mixture on high until it was cool, thick, and frothy.

At that point we had two colloids: the yolk foam and the white meringue.  We folded the two together, taking care not to destroy the carefully created air pockets.

Finally, we folded in the ganache mixture.  The result war a silken, pillowy soft chocolate mousse.   We let the mousse set in the fridge before digging in, and meanwhile we concocted our sourdough starter (more details to come later).

Our colloidal experience was wildly successful; we constructed and maintained a perfect amount of microscopic air pockets for a delicate mousse, and the mixture came together seamlessly.  In all, it was a delectable day.

Here's the recipe we used:

Chocolate Mousse

Six to eight servings

• 6 ounces (170g) bittersweet or semisweet chocolate, chopped

• 6 ounces (170g) unsalted butter, cut into small pieces

• 1/4 cup (60ml) dark-brewed coffee

• 4 large eggs, separated

• 2/3 cup (170g), plus 1 tablespoon sugar

• 2 tablespoons (30ml) dark rum

• 1 tablespoon (15ml) water

• pinch of salt

• 1/2 teaspoon vanilla extract

Adapted from Mastering the Art of French Cooking (Knopf) by Julia Child.

I tried to reduce the amount of butter in the recipe and found it wasn’t nearly as good. Since I’m not one to argue with Julia, I stuck close to the recipe tweaking it just slightly.

1. Heat a saucepan one-third full with hot water, and in a bowl set on top, melt together the chocolate, butter and coffee, stirring over the barely simmering water, until smooth. Remove from heat.

2. Fill a large bowl with ice water and set aside.

3. In a bowl large enough to nest securely on the saucepan of simmering water, whisk the yolks of the eggs with the 2/3 cup of sugar, rum, and water for about 3 minutes until the mixture is thick, like runny mayonnaise. (You can also use a handheld electric mixer.)

3. Remove from heat and place the bowl of whipped egg yolks within the bowl of ice water and beat until cool and thick, as shown in the photo above. Then fold the chocolate mixture into the egg yolks.

4. In a separate bowl, beat the egg whites with the salt until frothy. Continue to beat until they start to hold their shape. Whip in the tablespoon of sugar and continue to beat until thick and shiny, but not completely stiff, then the vanilla.

5. Fold one-third of the beaten egg whites into the chocolate mixture, then fold in the remainder of the whites just until incorporated, but don’t overdo it or the mousse will lose volume.

6. Transfer the mousse to a serving bowl or divide into serving dishes, and refrigerate for at least 4 hours, until firm.

For more on the chemistry of the meringue, refer to the foams post!

The Foams: Whipped Cream and Meringue

A foam is a gas trapped in the structure of some nutrient.  Some are created using fats, others by proteins, and still other by water.  Two very popular foams are whipped cream and meringue.  The former consists of milkfats whipped to encompass air bubbles, while the latter uses the proteins of egg whites.  Before we delve into the dark recesses of the chemistry of foams, here are the recipes!  No matter what is happening on a molecular level, they taste great!

For the whipped cream:

Ingredients:

2 tbsp granulated sugar (slightly more for a sweeter cream)

1 cup heavy whipping cream

Directions

Chill a mixing bowl in the freezer for 15 minutes.

Combine sugar and cream in chilled mixing bowl.  Starting on low speed, beat with an electric mixer until foamy.

Gradually increase speed to high and beat until stiff peaks form.  Tadaaaaa!  Foamy deliciousness!

For the meringue:

Ingredients:

4 egg whites (pasteurized if you are concerned about diseases)

1 cup granulated sugar

1/4 tsp cream of tartar

Directions:

Let ingredients come to room temperature.

Combine ingredients in a large bowl (copper if possible).

Beat with electric mixer, starting on low and gradually increasing speed until stiff peaks form.

Here are a few ideas for how to use your delightful concoctions:

• Make a mousse from the whipped cream
• Top  a pumpkin pie with the whipped cream
• Make Baked Alaska with the meringue
• Dollop the meringue on a lemon meringue pie
• Pipe the meringue into cookies and bake

Sourdough Starter

Sourdough at first glance seems to be an involved process.  However, it is a simple matter of coming prepared ahead of time, or having a bit of patience.  This recipe utilizes both microorganisms and foaming; the fermentation of the yeast falls into both categories.  The yeast can be quite finicky, so it's important to keep them in conditions appropriate to their biological niche.  Thus, don't heat the water about 115 degrees F and refrain from adding salt, as both would harm or kill the fragile microorganisms.  Best of luck!

Ingredients

3 cups water, 110 degrees F

1 1/2 tbsp active dry yeast

1 tbsp sugar

3 cups all purpose flour

Directions

 Bloom yeast, warm water, and sugar in a large bowl.  Let stand five to ten minutes until foamy.

Mix in flour with a whisk, stirring to incorporate air.

Cover with a tea towel and place in a warm area overnight.  At this point you may use the starter to make bread or keep it stored in the fridge in an airtight container.  To keep the starter going after removing some for use, replace the used quantity with an equal amount of flour and water.  

A Quick Preview

 Though we have not started our project, I thought it would be fun to give a preview of a couple of the goods we plan to bake.  Above are the homemade marshmallows... Mmmmmm...

Imagine them, served smooshed in between melty chocolate and sweet graham crackers.

Delicious, I know.

And then we have the famous polka dot cake.  We are so excited for this acid/base reaction!

It's made by baking cake balls (different renditions of colored velvet cakes) and then placing them in the midst of a greater cake.  It's almost too cute to eat!  Almost.

Welcome!

Hello and welcome to the Chemists in the Kitchen!  We chemists, Molly and Sarah, are embarking on a journey to cook and bake our way through the kitchen.  On this blog, we will attempt to explain the process of cooking through scientific principles.  We hope you enjoy our culinary confections and learn about the chemical means with which they were created!