Intro: Whipped Chocolate With Carbonated Strawberries
Whipping chocolate is a very simple process. All whipping up a foam requires is a fat, water and sugar (or another material) to stabilize the mixture. You don't even need to add eggs! It creates a new texture while making it easier to infuse different flavors into the chocolate.
While carbonating fruit may be a little more tricky, it isn't rocket science (although there is a certain amount of science involved). All you need to do is compress enough carbon dioxide gas in the presence of the fruit in order to force the carbon dioxide into the fruit.
Here are directions to making an interesting new treat.
Step 1: Making a Foamy Emulsion
The theory behind whipped chocolate is the same as that for whipping cream up into a foam. You must start with an emulsion of fat and water. Air is forced into the cream (or chocolate) by beating. Then, instead of the air leaving the cream, the fat droplets stop it from reaching the surface. Thus, little bubbles are created inside of the cream, supported by the fat. The cream swells up and voila, you have whipped cream: an airy substance able to support its own weight without collapsing.
So what we have to do is create a fat emulsion imitating cream and it should whip up into a foam. The way you make chocolate imitate cream is make sure the chocolate has the right amount of fat and water. About 70% cocoa solids works well, so use dark chocolate. Then we melt it all down in order to homogenize it, spreading all of the ingredients out equally within the liquid.
Step 2: Materials for Whipped Chocolate
When we tried this recipe, we started with the whipped chocolate recipe on the molecular gastronomy blog Khymos. We decided to try a few additions to the recipe. You can change this recipe around as long and the water/chocolate ratio stays the same. If you add more fat, you may need to increase the water as well. (When we say "water" here, we include whatever water-based liquid you may choose . . . coffee, fruit juice, chai, etc.)
8 oz of 70% dark chocolate
6 oz of hot coffee
3 tablespoons of bacon fat - try this, we dare you!
(Save the bacon for garnish).
A hand held electric beater. A Kitchen Aid or similar mixer will not work, because it doesn't go fast enough to really whip the chocolate.
A bowl to whip the chocolate in.
A bowl for ice, big enough to accommodate the bowl of chocolate.
Step 3: How to Make the Whipped Chocolate
Chop the chocolate into little pieces to make sure it melts easily. Then put the chocolate in a bowl and add the hot coffee. Let it sit for a few minutes to give the chocolate a chance to melt. Then stir the mixture until it becomes smooth and the chocolate is completely dissolved. Add the bacon fat to the mixture and stir until it is completely incorporated.
Fill a bowl with ice and put the bowl of chocolate on top of the bowl of ice. Then stir the chocolate until it gets thick enough so that if you lift your stirring implement and let of stream of chocolate fall down in the bowl, you can still see the shape of the stream. This should take about 10 minutes or so.
As soon as you have achieved this, set your hand beater to a high setting and beat the chocolate. Keep beating until it gets very thick and is able to somewhat support its own weight. When you first start whipping it, it will not change very much for the first few minutes. Then the texture will change a lot all of a sudden, so pay attention. You can store the whipped chocolate in the refrigerator while you carbonate the fruit.
Step 4: How Is It Possible to Carbonate Strawberries?
Now it is time to carbonate the strawberries. What we are going to do is place dry ice in a semi-sealed environment to force the gas to dissolve in the moisture of the fruit. When the dry ice sublimates, it will build up pressure. Both the enclosed environment and the increased pressure effectively serve to increase the carbon dioxide gas concentration. The increased gaseous carbon dioxide concentration drives more carbon dioxide to dissolve in the moisture on the surface of the fruit.
Step 5: Materials for Carbonated Strawberries
1/2 lb. of strawberries, washed, cored, and sliced (or pears worked even better)
approximately 4 lbs. of dry ice
a pressure cooker
a dish small enough to fit in the pressure cooker
Arrange the prepared fruit in a thin layer face up on a flat dish. Note the importance on placing them face up so they will absorb more carbon dioxide. The dish should be small enough to fit into your pressure cooker. (As a note, you should probably use a plate you don't care much about considering it could be damaged by the extreme cold of the dry ice). Wearing protective gloves and goggles to avoid cold burns, crack up the dry ice and place several pieces in the bottom of the pressure cooker. Add the bottom insert, then a couple of layers of paper towel. Place the plate in the pressure cooker on top of the paper towels. You don't actually want your fruit to freeze, so you are trying to keep it well above the dry ice.
Step 6: The Process of Carbonating the Strawberries
Add a little water to the pressure cooker with dry ice and strawberries, and seal it up. As the dry ice sublimates (goes from solid to gas), pressure should build up in the pressure cooker, and you will hear it venting. If it vents too quickly, you may want to place it on some styrofoam so it heats up slower. If you loose pressure but it's still very cold, you may want to place it where it's warmer so the ice sublimates faster. If you lose pressure and it's getting warmer, you may need to add more dry ice. We weren't able to keep the pressure up constantly, we just did our best. Whatever you do, don't open a pressure cooker that's still under pressure. This is the tricky part. You will need to tweak and watch the pressure cooker for about 30 minutes (or more, if you can't get the darned thing to lose pressure so you can open it). Make sure your vent doesn't freeze shut during this process. Don't worry, if your fruit freezes, it's still tasty. If the strawberries have frozen, allow them to partially thaw. Serve them immediately so that the carbonation inside of them doesn't have a chance to escape.
Step 7: Use Less Acidic Fruit for the Best Results
We found that only the tips of our strawberries were carbonated. We think this was because our fruit was rather sour (acidic) except for at the tips. If you try strawberries, be sure they're ripe and sweet. The carbon dioxide gas forms carbonic acid in water, increasing the acidity of the liquid in the fruit. Since this is an equilibrium reaction, if the fruit is already acidic, less carbon dioxide will dissolve and it won't become as carbonated as it might. The reaction is forced to the left. This may be why less acidic pears worked very well. Grapes and watermelons should work well, too, but to accompany our whipped chocolate we wanted strawberries.
Step 8: In Conclusion
Adding these two together makes a great pair. We served it with whipped cream and bacon bits. Unless we told people in advance, they didn't really notice the bacon flavor in the chocolate. It blended in very nicely and added to the richness of the dish, which was considerable. Do please take a risk and try it with bacon bits. This is a VERY rich dessert and needs the balancing tart carbonated fruit or salty bursts of bacon to avoid overwhelming the palate. Portions should be very small. We suggest the whipped chocolate could be spread on waffles, used to fill truffles, or even used as a frosting or to top hot mocha (without the bacon bits, of course!).
Tweak this recipe as you wish.
Second Prize in the
Hungry Scientist Contest