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Aquafaba Meringues

Photo credit: veganbaking.net (vegan-baking/Flickr)

Photo credit: veganbaking.net (vegan-baking/Flickr)

Dr. Kent Kirshenbaum flew from NYC to LA to speak at our March 8th public lecture about the impact of what we eat, sharing the stage with Dr. Amy Rowat, Dr. Paul Thompson, and Chef Daniel Patterson. Impressively he brought along with him a case of hundreds of homemade vegan meringues for lecture attendees to nosh on after the event.

In lieu of egg whites, the meringues contained aquafaba, the liquid from canned chickpeas. To the surprise and delight of Science & Food guests, the airy confections were devoid of any chickpea flavor. Some reached for seconds (or guilty thirds) while others wondered how Dr. Kirshenbaum was able to transport the fragile cookies across the country without any of them breaking. (Note from backstage: all the cookies were in mint condition when we received the case from Dr. Kirshenbaum–until moments before the event when one of us volunteers fumbled during setup and dropped one. Oops!)

Whether you want to recreate Dr. Kirshenbaum’s aquafaba meringues because you loved them so much or you couldn’t make the event, we have the recipe below!

A Science & Food volunteer offers lecture attendees Dr. Kent Kirshenbaum's amazing vegan meringues.

A Science & Food volunteer offers guests Dr. Kent Kirshenbaum’s amazing vegan meringues.
Photo credit: Abbie F. Swanson (@dearabbie/Twitter)

Aquafaba Meringues

1/2 to 3/4 cup of liquid drained from a 15 oz can of chickpeas
1/2 cup sugar

1. Preheat oven to 215 °F.

2. Using an electric mixer, beat the canned chickpeas liquid at high speed until stiff peaks form.

3. Once peaks have formed, add sugar one tablespoon at a time. After all the sugar is incorporated, if the foam feels gritty, keep whipping until the mixture is smooth.

4. Spoon or pipe the meringue in 1.5 inch dollops onto parchment paper-lined baking sheets.

5. Bake at 215 °F for 1.5 hours.

6. After baking, turn off the oven and crack the oven door open to allow the cookies to cool to room temperature. Store cookies in an airtight container.


Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


Homemade Marshmallows

Photo Credit: Heather Katsoulis (hlkljgk/Flickr)

Photo Credit: Heather Katsoulis (hlkljgk/Flickr)

Whether you prefer them toasted over a campfire, bobbing in a cup of hot chocolate, or roasted over a bed of sweet potatoes, marshmallows are an ooey-gooey fluffy treat that just finds a way warm the cockles of your heart.

Marshmallows, like other well-known aerated confections – think mousses, ice cream, meringues –  are essentially made of four basic components: sugar, water, air, and a hydrocolloid.  Hydrocolloids, often called “food gums” are polysaccharides, or typically large-branching proteins, that form thick gels when they interact with water. [1]

Their ability to bind to water molecules makes them hydrophilic (or “water-loving”), and their ability to remain suspended and dispersed evenly in the water (without settling to the bottom) makes the substance a colloid. Thus, food gums are hydrophilic colloids, or hydrocolloids.

Photo Credit:  Daniel Campagna (Chefpedia)

Photo Credit: Daniel Campagna (Chefpedia)

Hydrocolloids are added to many foods we eat – as thickening agents in pie fillings or gravies, gelling agents in puddings and jams, foam stabilizers in beer and meringues, film formers in sausage casings, emulsifiers in salad dressing, and even fat replacers in frostings and muffins.  Common examples of hydrocolloids are starch, xanthan gum, locust bean gum, alginate, pectin, carrageenan, and agar, which all influence the texture and mechanical stability of many foods.  [1][2]

In marshmallows, the hydrocolloid responsible for the chewy, bouncy texture we know and love is gelatin. While gelatin is one of the most popular commercial hydrocolloids, it is definitely not the most glamorous.  Gelatin is made of collagen, which is the structural protein derived from animal skin, connective tissue, and bones. In fact, mainstream gelatin is usually obtained from pigskin, cattle bones, and cattle hide. [3] Gelatin is unique because not only does it function as a foam stabilizer for the marshmallows [4], but when it is mixed with water, gelatin forms a thermally-reversible gel.  These gelatin gels have a melting temperature just below body temperature (< 35°C or 95 °F), so the gel product literally melts in your mouth and releases intense flavor immediately as it dissolves, which is a difficult quality to replicate with other hydrocolloids. [3]  

Gelatin makes marshmallows chewy by forming a tangled 3-D network of polymer chains.  Once gelatin is dissolved in warm water (dubbed the “blooming stage”), it forms a dispersion, which results in a cross-linking of its helix-shaped chains.  The linkages in the gelatin protein network, called “junction zones” trap air in the marshmallow mixture and immobilize the water molecules in the network . The result? The famously spongy structure of marshmallows! [1]  This is why the omission of gelatin from a homemade marshmallow recipe will result in marshmallow crème, since there is no gelatin network to trap the water and air bubbles.

And for the gelatin-averse, worry not! There are indeed many hydrocolloid alternatives to gelatin. However, since gelatin has so many different functions (gelling agent, emulsifier, stabilizer, thickener, etc.), its alternatives are not universal. Rather, substitutes are specific to each specific food application. In our case, some have suggested pectin – a polysaccharide from the cell walls of plants – as the ideal replacement for gelatin in marshmallows [1].

Agar agar is a commonly used vegetarian alternative for jellies.  Photo Credit: I Believe I Can Fry (johnnystiletto/Flickr)

Agar agar is a commonly used vegetarian alternative for jellies.
Photo Credit: I Believe I Can Fry (johnnystiletto/Flickr)

Pectin, carrageenan (a polysaccharide from red seaweeds), or combinations of both can replicate the elastic texture and intense flavor release that gelatin provides for marshmallows. However, since the melting points of both pectin and carrageenan are not the same as the melting point of gelatin – which, as you recall, is slightly below body temperature, marshmallows made with pectin or carrageenan don’t have the quite the same “melt-in-your-mouth” sensation. [1]

* Note: Carrageenan gels are unique in that their melting temperature can be modified, depending on the solution concentration of the carrageenan and the presence of cations, so the melting temperature ranges from 40°C (104°F) and 70°C (158°F).

* Note: Carrageenan gels are unique in that their melting temperature can be modified, depending on the solution concentration of the carrageenan and the presence of cations, so its melting temperature ranges from 40°C (104°F) and 70°C (158°F).

As you can see, none of the gelatin alternatives have the appropriate melting temperatures to replicate gelatin’s melt-in-your-mouth sensation. However, this does prove advantageous in the fact that they can last longer on hot days or in hot, tropical climates and they do not require refrigeration to set.

No matter what you prefer for as a hydrocolloid, pillowy marshmallows can made with the same basic recipe:

Photo Credit: Joy (joyosity/Flickr)

Photo Credit: Joy (joyosity/Flickr)

Ingredients

For the bloom:
3 tablespoons (typically 3 packets) unflavored gelatin powder
1/2 cup cold water

*Vegan Substitution: 2 ½ tablespoons agar agar + ½ cup and 2 tablespoons water
Alternatively, this vegan marshmallow recipe is worth checking out:

For the marshmallows:
3/4 cup water
1 1/2 cups granulated sugar
1 1/4 cup sugar cane syrup or corn syrup
Pinch of salt

For the marshmallow coating:
1 1/2 cups powdered sugar
1/2 cup cornstarch
non-stick cooking spray


Equipment
Bowls and measuring cups
Fork or small whisk
9×13 baking pan or other flat container
4-quart saucepan (slightly larger or smaller is ok)
Pastry brush (optional)
Candy thermometer
Stand mixer with a wire whisk attachment
Stiff spatula or spoon (as opposed to a rubbery, flexible one)
Sharp knife or pizza wheel

Instructions

  1. Prepare pans and equipment: Spray the baking pan with cooking spray. Use a paper towel to wipe the pan and make sure there’s a thin film on every surface, corner, and side. Set it near your stand mixer, along with the kitchen towel and spatula. Fit the stand mixer with the whisk attachment.
  2. Bloom the gelatin/agar: Measure the gelatin or agar into the bowl of the stand mixer. Combine 1/2 cup cold water in a measuring cup and pour this over the gelatin or agar while whisking gently with a fork. Continue stirring until the gelatin or agar has dissolved or reached the consistency of apple sauce and there are no more large lumps. Set the bowl back in your standing mixer. (Alternatively, you can bloom the gelatin or agar in a small cup and transfer it to the stand mixer.)
    * NOTE: You can add about 1 tablespoon of powdered flavorings to your hydrocolloid while it is blooming in the water.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  3. Combine the ingredients for the syrup: Pour 3/4 cup water into the 4-quart saucepan. Pour the sugar, corn syrup, and salt on top. Do not stir.
  4. Bring the sugar syrup to a boil: Place the pan over medium-high heat and bring it to a full, rapid boil — all of the liquid should be boiling. As it is coming to a bowl, occasionally dip a pastry brush in water and brush down the sides of the pot. This prevents sugar crystals from falling into the liquid, which can cause the syrup to crystallize. If you don’t have a pastry brush, cover the pan for 2 minutes once the mixture is at a boil so the steam can wash the sides.
    Do not stir the sugar once it has come to a boil or it may crystallize!
  5. Boil the syrup to 247°F to 250°F: Clip a candy thermometer to the side of the sauce pan and continue boiling until the sugar mixture reaches 247°F to 250°F. Take the pan off the heat and remove the thermometer.
  6. Whisk the hot syrup into the gelatin / agar: Turn on your mixer to medium speed. Carefully pour the hot sugar syrup down the side of the bowl into the gelatin or agar. The mixture may foam up — just go slowly and carefully.
  7. Increase speed and continue beating: When all the syrup has been added, cover the bowl with a clean kitchen towel and increase the speed to high (the cloth protects from splatters — the cloth can be removed after the marshmallows have started to thicken).

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  8. Beat marshmallows until thick and glossy: Whip for about 10 minutes. At first, the liquid will be very clear and frothy. Around 3 minutes, the liquid will start looking opaque, white, and creamy, and the bowl will be very warm to the touch. Around 5 minutes, the marshmallow will start to increase in volume. You’ll see thin, sticky strands between the whisk and the side of the bowl; these strands will start to thicken into ropes over the next 5 minutes. The marshmallow may not change visually in the last few minutes, but continue beating for the full 10 minutes. When you finish beating and stop the mixer, it will resemble soft-serve vanilla ice cream.
    * NOTE: Add 1- 2 tablespoons of liquid flavorings during the last couple minutes of the beating process. (See Ideas Section below.)
  9. Immediately transfer to the baking pan: With the mixer running on medium, slowly lift (or lower, depending on your model) the whisk out of the bowl so it spins off as much marshmallow as possible. Using your stiff spatula, scrape the as much of the thick and sticky marshmallow mixture into the pan as you can.
    * NOTE: If you want mini marshmallows, after mixing, immediately put the mixture in a piping bag and pipe out your mini marshmallows in the size and shape of your choice.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  10. Let the marshmallows set for 6 to 24 hours: Spray your hands lightly with cooking oil and smooth the top of the marshmallow to make it as even as possible. Let the mixture sit uncovered and at room temperature for 6 to 24 hours to set.
  11. Prepare the marshmallow coating: Combine the powdered sugar and cornstarch in a bowl.
  12. Remove the marshmallows from the pan: Sprinkle the top of the cured marshmallows with some of the powdered sugar mix and smooth it with your hand. Flip the block of marshmallows out onto your work surface. Use a spatula to pry them out of the pan if necessary. Sprinkle more powdered sugar mixture over the top of the marshmallow block.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  13. Cut the marshmallows: Using a sharp knife or pizza wheel, cut the marshmallows into squares. It helps to dip your knife in water every few cuts. (You can also cut the marshmallows with cookie cutters.)
  14. Coat each square with powdered sugar mix: Toss each square in the powdered sugar mix so all the sides are evenly coated.

    Photo Credit: Joy (joyosity/Flickr)

    Photo Credit: Joy (joyosity/Flickr)

  15. Store the marshmallows: Marshmallows will keep in an airtight container at room temperature for several weeks. Leftover marshmallow coating can be stored in a sealed container indefinitely.

Ideas:

  • Add Flavorings: You can add about a tablespoon of either powdered or liquid flavorings/food colorings to the marshmallows at Step 2 or Step 8, respectively, in the recipe.
  • Sweet Marshmallows
    – classic: vanilla extract, almond extract, cocoa powder
    – floral: rose water, orange blossom water
    – spiced: cinnamon, pumpkin spice, cardamom, nutmeg, chai tea, peppermint
    – fruity: passion fruit, strawberry, mango, lemon juices
  • Savory Marshmallows
    –  A great base for savory marshmallows: PopSci:Sechuan Peppercorn Marshmallow
    – garlic salt and pepper
    – pesto (I’m imagining a pillowy caramelized pesto-marshmallow roasted on top of a pizza!)
    – hot sauce
  • Add citric acid or cream of tartar to stabilize the inverted sugars in your recipe and prevent them from crystallizing, essentially ensuring that your marshmallows remain fluffy and chewy.
  • Add your sugar syrup into whipped egg whites to incorporate extra air volume and structure for spongier, pillowy marshmallows.
  • DIY Lucky Charms: You can make your own dehydrated marshmallows, similar to the ones found in breakfast cereals (but without all the suspicious additives) by evaporating the water from the sugar solution in your homemade marshmallows.  Various methods are described here.


Recipe adapted from

References Cited

    1. Saha, D., Bhattacharya, S. Hydrocolloids as thickening and gelling agents in food: a critical review. Journal of Food Science and Technology. December 2010; 47(6): 587-597.
    2. Gum“. Food @ OSU.
    3. Karim, A. A., Bhat, R. Gelatin alternatives for the food inudustry: recent developments, challenges and prospects. Trends in Food Science & Technology. December 2008; 19(12): 644-656.
    4. Gelatin. Gelatin Food Science. 14 Dec. 1998.

Eunice LiuAbout the author: Eunice Liu is studying Neuroscience and Linguistics at UCLA. She attributes her love of food science to an obsession with watching bread rise in the oven.

Read more by Eunice Liu


Tri-Color Potato Salad

“There’s so much great food yet to discover that we can grow, so I just love discovering new varieties, crops, things that our customers and myself have never tried before.”
                                                                          – Alex Weiser, 2013 Science & Food course Read more

Fancy Chocolate Treats

Photo credit: Jesús Rodriguez (hezoos/Flickr)

Photo credit: Jesús Rodriguez (hezoos/Flickr)

Chocolate-covered strawberries have an innate beauty in their simplicity, making this snack both sweet and decadent. But this gourmet treat does not have to be expensive nor only savored at special events. Although it’s not quite as simple as dipping strawberries into soupy chocolate sauce, you can easily make chocolate-covered strawberries in your very own kitchen with a basket of strawberries, a bag of chocolate, and a little patience.

To perfect the crafting of chocolate-covered strawberries, it helps to first consider the composition of chocolate. Chocolate contains only a few ingredients: fat, sugars, proteins, and soy lecithin as emulsifier that holds everything together [1,2]. Cocoa butter, a fat that is derived from cocoa beans, makes up the majority of chocolate. Like many vegetable fats, cocoa butter is a mixture of fatty molecules called triacylglycerols. Different types of triacylglycerols—saturated, monounsaturated, polyunsaturated—have their own thermal and structural properties. Roughly 80% of cocoa butter are monounsaturated triacylglycerols [3]. The secret to chocolate perfection lies in the microscopic arrangement of these molecules. The texture (smooth vs. lumpy), appearance (glossy vs. dull), and melting temperature of chocolate (in your mouth at 98°F vs. in your hand at 82°F) all depend on how triacylglycerols pack together in the finished chocolate product.

Triacylglycerols are elongated, spindly molecules that can be packed together in different ways, sort of like long, skinny Legos. The three main ways that triacylglycerols can pack together are named α, β’, and β [3]. A pure mixture of triacylglycerols will form the most stable structure, β [4], and quality chocolate that is hard, smooth, and shiny will predominantly contain this β structure. Unfortunately, cocoa butter isn’t purely one type of triacylglycerol: while the 80% monounsaturated triacylglycerols will tend to pack together nicely into perfect β structures,  the other 20% of cocoa butter fat molecules can interfere and lead to less stable α or β′ structures. As shown in Table 1, chocolate can take on different combinations of α, β′, and β structures, categorized in order of increasing stability as crystals I-VI [2,3]. Crystal V possesses only the β structure, and so it boasts the most desirable chocolate characteristics, such as good sheen, satisfying snap, and melt-in-your-mouth smoothness.

Table 1. Properties of chocolate crystals (adapted from [2]).

Crystal Structure Melting Temp (°F) Chocolate Characteristics
I β′sub(α) 63 Dull, soft, crumbly, melts too easily
II α 70 Dull, soft, crumbly, melts too easily
III β′2 79 Dull, firm, poor snap, melts too easily
IV β′1 82 Dull, firm, poor snap, melts too easily
V β2 93 Glossy, firm, best snap, melts near body temp
VI β1 97 Hard, takes weeks to form

Unfortunately, getting chocolate to form the desired crystal type is easier said than done. When chocolate is melted and then left alone to re-harden on its own terms, uncontrolled crystallization occurs: any and all of the six crystal types will form at random. Chocolate that has been allowed to set this way ends up clumpy and chalky. To control crystallization and select for crystal V, the chocolate must be tempered. Through the tempering process, chocolate is first heated to 110-130°F to melt all the different crystal types. Most importantly, the temperature has to be higher than 82°F to melt the inferior crystals I-IV. Melted chocolate is then cooled down by adding “seeds” of chocolate that already contain only crystal V. These seeds are usually just pieces of chocolate that has already been tempered. Any piece of chocolate—chips, buttons, or chopped— can be used, as the majority of chocolate on the market has already been tempered. These seeds slowly cool the melted chocolate and act as a molecular template from which additional crystal V structures can grow [3]. As the chocolate cools, the stable crystal V will come together into a dense, even network, creating that lustrous, firm chocolate coating.

But beware: a drop of water can ruin all that hard work and perfectly tempered chocolate by causing it to seize. During the manufacturing process, water is removed from the chocolate, leaving behind a blend of fats and sugars. Introducing water to melted chocolate causes the sugar molecules to clump together in a process known as seizing [1]. These wet, sticky sugar clusters result in a grainy, thick batch of chocolate.

Seizing can happen when chocolate is melted in a double boiler, as water from the steam can get into the chocolate. It can also happen when pockets of chocolate are accidentally burnt. Burning is a chemical reaction that oxidizes the fats and sugars to produce carbon dioxide and water. Water that forms in the burnt pockets of chocolate will cause the rest of the batch to seize. But have no fear! Seized chocolate is not completely ruined: it can be saved by adding even more water or other liquids such as cream. Though it may seem counterintuitive, adding more water actually dissolves the sugar clumps, breaking them apart so that the chocolate can become smooth and creamy again [1]. Unfortunately, because there is now moisture in the chocolate, it will not dry and harden into a chocolate shell anymore. Chocolate rescued in this way can be used for hot chocolate, icings, fillings, or ganaches, which means you can still make an impressive chocolate treat even if the chocolate-covered strawberries don’t work out.


Chocolate-Covered Strawberries

1 lb. strawberries
16oz milk chocolate chips
Thermometer (optional, but would be helpful)

1. Melt half to two-thirds of the chocolate chips…

…In a double boiler: Stir constantly. Be sure steam doesn’t escape and sink into the chocolate. Do not cover.

…In the microwave: Heat on high 1 minute. Do not cover. Remove from the microwave and stir. If all the chocolate has not melted, heat again for 5-10 seconds. Repeat until completely melted
Note: If possible, avoid using a heat-retaining container like glass, which may burn the chocolate. Plastic is preferred.

2. Once completely melted, carefully continue heating until the temperature is 90-95°F.

3. Remove from heat, then add chocolate chips. Stir until the chips have melted and the chocolate is 82-88°F.

4. To test if the chocolate is ready, spread a thin layer on the back of a spoon or a piece of paper. It should harden in less than 3 minutes. If it doesn’t, stir in more chocolate chips.

5. When the chocolate is ready, carefully dip in strawberries. Make sure the strawberries are dry, before dipping. Allow dipped strawberries to dry on a sheet of parchment paper.


References Cited

  1. Corriher, S. Chocolate, Chocolate, Chocolate. American Chemical Society: The Elements of Chocolate. October 2007; <http://acselementsofchocolate.typepad.com/elements_of_chocolate/Chocolate.html>
  2. Loisel C, Keller G, Lecq G, Bourgaux C, Ollivon M. Phase Transitions and Polymorphism of Cocoa Butter. Journal of the American Oil Chemists’ Society. 1998;  75(4): 425-439.
  3. Rowat A, Hollar K, Stone H, Rosenberg D. The Science of Chocolate: Interactive Activities on Phase Transitions, Emulsification, and Nucleation.  Journal of Chemical Education. January 2011; 88(1): 29-33.
  4. Weiss J, Decker E, McClements J, Kristbergsson K, Helgason T, Awad T. Solid Lipid Nanoparticles as Delivery Systems for Bioactive Food Components. Food Biophysics. June 2008; 3(2): 146-154

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.


Ceviche

Through the process of cooking, molecular transformations alter the macroscopic properties of our food. Consider what happens when you fry an egg: the transparent, liquid egg whites become an opaque white solid. These striking changes in the egg’s color and texture are a result of protein denaturation. Read more