March 2015 – Science and Food

Science of Marinades

March 31, 2015/in Science & Food/by Grant Alkin

Chicken Tikka Masala, Beef Bulgogi, and Ceviche all have one thing in common: each protein is marinated, which contributes to the development of flavors and textures in the final dishes. The use of marinades is common across all cultures, and can provide a unique kick to food when done correctly.

Rostbrätel: marinated cutlet of pig neck. Photocredit: (Sebastian Wallroth/Wikimedia Commons)

What is marination?

Marination is the process of immersing foods in a liquid often made with oil, seasonings, and an acid or enzymatic component, to flavor and tenderize food. This liquid is called a marinade, and the term originally came from the use of seawater to preserve meat. The roots of the word are derived from the Latin word for sea (mare) [1].

Why is marination useful?

To understand the importance of marination, we must first address the components of raw meat. Consider tough, lean cuts of meat such as shank or flank. Meat toughness is related to the collagen and elastin fiber content in its connective tissues. One way to tenderize lean meat is with moist heat, as this breaks down stiff collagen proteins into soft, soluble gelatin [2]. Gelatin is responsible for that silky, falling-apart texture and mouthfeel [3]; this can be achieved with braising and stewing, where meat is simmered in liquid at a low temperature, allowing collagen to dissolve starting at 160º F. However, this conversion process can take some time, even up to 72 hours. Another reason to pre-tenderize meat before cooking is to prevent dried out meat: moisture is lost when heat is applied (despite being cooked in liquid).

This is where marination comes into play, as it provides another opportunity for protein breakdown. This method can thus shorten subsequent cooking time as well as minimize moisture loss as less heat is needed to “cook” the meat. Two types of marination include acidic and enzymatic marination, which both help break down the connective tissue in the meat.

Acidic marination

Acids, such as lemon juice or vinegar, work by denaturing proteins through disruption of hydrogen bonds in the collagen fibrils. Adding alcohol can also supplement the penetration of acid marination since fats present in meat are soluble in alcohol [4]. Beer and wine thus make great marinades, and they also confer their own tenderizing agents (tannins). Be careful not to overmarinate the meat, as prolonged exposure to acid can cause it to become tough. This occurs because after the proteins are denatured, they tighten as water content decreases [5]. Some marinades involve milk or yogurt since they have lower acid content.

Shrimp Ceviche, a dish that uses acidic marination. Photo Credit: Carlos Lopez (cloalpz/Flickr)

Enzymatic marination

Enzymes increase the rate at which cellular reactions occur, and certain enzymes help attack the protein networks of tough meat. Proteolytic enzymes such as fungal amylase (in legume seeds) and protease (in ginger) help break down muscle fiber protein into its constituent amino acids. Enzymes from tropical plants such as bromelain (in pineapple), papain (in papaya) and ficin (in latex of fig tree) break down collagen and elastin [4]. In fact, natives of pre-Columbian Mexico used to wrap their meat in papaya leaves before cooking since they found that it increased tenderness [6]. However, be sure to monitor the time of marination, for the enzymes can completely digest meats if they sit for too long.

Papaya contains papain, a proteolytic enzyme. Photo credit: Tatiana Gerus (Tatters/Flickr)

Adsorption

Another factor to take into account is the amount of contact the meat has with the marinade. Marination is a process of adsorption, where the marinade adheres to the outer surface of the meat rather than absorption, where it would penetrate all the way through [7]. This has resulted in some controversy over whether acidic and enzymatic marinades actually tenderize meat or not, but there are ways to alleviate this problem. It may be helpful to use thinner slices of meat to enhance the marinade penetration and reduce marination time. For thicker cuts, marinades can be injected to increase contact surfaces. Adding salt also helps, as it first draws out liquid by osmosis; then the resultant brine is reabsorbed into the meat while breaking down muscle structure. The brine draws flavors further down below the surface [8]. Fat such as oils are also useful to transfer fat-soluble flavors from the seasonings into the meat.

In general, tender cuts of meat should not require as much marination time as tougher cuts, and fish require even less time. Marinated meats should also be refrigerated to prevent harmful bacterial growth. Although it may seem a hassle to prepare ingredients for a marinade and remember to apply it to the meat for a certain time beforehand, the results can be well worth the wait.

References cited

Some Surprising Facts About Marinades and the Origin of the Word. CulinaryLore.
Collagen. About Food.
Science of Slow Cooking. Science of Cooking.
Juáres, M., Aldai, N., López-Campos, Ó., Dugan, M., Uttaro, B., Aalhus, J. Beef Texture and Juiciness. Handbook of Meat Processing. January 2012.
Marinating Meats. Allrecipies.
Alarcón-Rojo, A. Marination, Cooking, and Curing: Applications. Handbook of Poultry Science and Technology, Secondary Processing. February 2010.
Saucy Science: Exploring the Science of Marinades. Scientific American.
The Food Lab: More Tips For Perfect Steaks. Serious Eats.

About the author: Catherine Hu is pursuing her B.S. in Psychobiology at UCLA. When she is not writing about food science, she enjoys exploring the city and can often be found enduring long wait times to try new mouthwatering dishes.

Read more by Catherine Hu

Cheese Microbes & Pizza Math

March 26, 2015/in What We're Reading/by Grant Alkin

Researchers at the American Academy of Microbiology answer the FAQs of cheese-making and Carl Friedrich Gauss, a famous 19th century mathematician, explains the best way to hold a pizza slice–using math, of course.
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The Science of Pie 2014: Video Highlights

March 24, 2015/in Public Lectures/by Grant Alkin

The Science of Pie 2014: Video Highlights

June 1, 2014

At the Science of Pie, the world’s first scientific bakeoff, the students of the Science & Food undergraduate course presented results from their final projects in poster format and their pies for taste testing. These pies had to be cooked in one hour and were the summation of all that the students had learned from their pie experiments in the class. Throughout the quarter, the students were challenged to perform a scientific investigation of apple pie and vary different features of the pie such as shape, butter size, and moisture.

The contest was judged by Lena Kwak (of Cup4Cup) and Dave Arnold (of Booker and Dax, the Museum of Food and Drink, and the Cooking Issues Podcast) who were our featured speakers for the 2014 Public Lecture Harnessing Creativity. They were joined by Nicole Rucker (Pastry Chef, Gjelina Take Away), Jonathan Gold (Food Critic, LA Times), Dr. Paul Barber (Associate Professor of Ecology and Evolutionary Biology, UCLA), and Dr. Rachelle Crosbie-Watson (Associate Professor of Integrative Biology and Physiology, UCLA).

The judges had wise words for the students.

Lena Kwak described how she judged the pies.

“With each of the projects we saw today, there were a considerable amount of variables not considered, but the saving grace …was when I tasted their pies.”

Nicole Rucker talked about what makes an award wining pie

“Jonathan and I both know that from Judging Pie Contests, … that you can see a good pie from literally across the room.”

Dr. Paul Barber spoke to the balance of science and pie making:

“No matter how much scientific testing you do, there’s still just this underlying art to making a really good pie.”

Check out some our featured pies from the 2014 contest.

Honorable Mention Pie

Alexis Cary & Matthew Copperman (Team On the Road)

Perfectly Unsoggy Apple Pie

Best Scientific Pie

Christina Cheung, Tori Schmitt, and Elliot Cheung (Team Pretty Intense Pie Enthusiasts)

Beer Crust Apple Pie

Best Overall Pie & People’s Choice Pie

Alina Naqvi & Ashley Lipkins-Scott (Team Apple Queens)

Crumbalicious Apple Pie

Check out our written recap here !

See the whole Video!

Beer

March 17, 2015/in Flavor of the Month/by Grant Alkin

Celebrating St. Patrick’s Day with a frosty glass of beer? Before taking that first sip, consider these quick facts about the science behind the many complexities in beer flavors. Now that’s something to raise your glass to! Read more

Beer Yeast & Flavor

March 11, 2015/in What We're Reading/by Grant Alkin

Want beer foam that doesn’t dissipate right away? Microbiologist Tom Villa made a genetic discovery in yeast that could create beers with longer-lasting beer foam. This yeast, however, doesn’t quite affect the taste, so find out where beer flavor comes from.
Read more

Vinaigrette

March 10, 2015/in DIY Kitchen Science/by Grant Alkin

Ingredients to make Greek salad dressing. Photo credit: Julle Magro (magro-family/Flickr)

Homemade vinaigrettes are about as easy as they look: mix oil, vinegar, and spices; shake before pouring. For those who want vinaigrettes without the inelegant step of shaking before serving, the solution is simple; add an emulsifier.

Understanding the role of an emulsifier first requires some familiarity with the primary components in vinaigrette, vinegar and oil. Vinegar is composed of acetic acid and water, which are polar compounds. In a polar molecule, one or a group of atoms have a stronger pull on the electrons in the molecule. Due to this uneven share of electrons between the atoms, weak charges form on opposite ends of the molecule [Figure 1a]. The weakly positive and negative charges on the polar molecule are called dipoles. Oil, on the other hand, is a type of lipid, which is a nonpolar compound. Since the atoms within the lipid are largely identical, the electrons are evenly distributed across the lipid molecule [Figure 1b]. Therefore, nonpolar molecules do not have such well-developed dipoles.

Figure 1. a) Acetic acid and water are polar molecules. b) Lipids are nonpolar molecules.

In solutions, compounds follow the chemistry fiat, like dissolves like. Polar molecules only interact with other polar molecules. Likewise, nonpolar molecules prefer to be surrounded by other nonpolar molecules. When a polar solution, like vinegar, is vigorously mixed with a nonpolar solution, like oil, the two initially form an emulsion, a mixture of polar and nonpolar compounds. However, this emulsion is unstable and will very quickly form layers in what’s known as phase separation. The solutions separate into layers according to their respective densities due to an aversion to each other. (In this case, because oil has a lower density than vinegar, it happens to be the layer floating on top.)

Phase separation in vinaigrette. Photo credit: Jan Persiel (janpersiel/Flickr)

To prevent phase separation, an emulsifier can be added to the vinaigrette to stabilize the emulsion. Emulsifiers are amphipathic compounds, meaning the molecule has both a polar and nonpolar section [Figure 2]. Common food emulsifiers include egg yolk, soy lecithin, garlic, and mustard. Egg yolk contains the emulsifying agent lecithin. The vegan version is isolated from soy and is thus known as soy lecithin. Lecithin is a commonly used emulsifier in many other food products, such as chocolates, mayonnaise, and Hollandaise sauce. Amphipathic compounds found in garlic include diallyl sulfide, allyl methyl disulfide, and diallyl trisulfide [1]. Mustard, the condiment, is made from mustard seeds. Emulsifying agents in the condiment, such as the pectin rhamnogalacturonan, originate from the mucilage of mustard seeds, a thick, glutinous layer that surrounds the seed hull [2,3].

Figure 2. a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

So with a helping hand from emulsifiers, homemade vinaigrettes can still be as simple yet elegant as they seem, and best of all, ready to serve whenever.

Greek Salad Vinaigrette (Recipe from Ina Garten’s Barefoot Contessa)

½ cup olive oil
¼ cup red wine vinegar
2 cloves garlic, minced
½ tsp Dijon mustard
½ tsp ground black pepper
1 tsp salt
1 tsp dried oregano

In a bowl, whisk together the vinegar, garlic, mustard, salt, pepper, and oregano until well mixed.
While still whisking, slowly add the olive oil.
When a stable emulsion forms, serve with salad or store in a covered bowl or bottle.

References cited

Kimbaris, A.C., Siatis, N.G., Pappas, C.S., Tarantilis, P.A., Daferera, D.J., Polissiou, M.G. Quantitative analysis of garlic (Allium sativum) oil unsaturated acyclic components using FT-Raman spectroscopy. Food Chemistry, 2006; 94: 287-295.
Cui, W., Eskin, M.N., Biliaderis, C.G., Marat, K. NMR characterization of a 4-O-beta-D-glucuronic acid-containing rhamnogalacturonan from yellow mustard (Sinapis alba L.) mucilage. Carbohydrate Research, 1996; 292(1): 173-183.
Leroux, J., Langendorff, V., Schick, G., Vaishnav, V., Mazoyer, J. Emulsion stabilizing properties of pectin. Food Hydrocolloids, 2003; 17: 455-462.

About 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

March 3, 2015/in DIY Kitchen Science/by Grant Alkin

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)

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)

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 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)

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

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.
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)
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.
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!
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.
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.
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)
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.)
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)
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.
Prepare the marshmallow coating: Combine the powdered sugar and cornstarch in a bowl.
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)
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.)
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)
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

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.
“Gum“. Food @ OSU.
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.
Gelatin. Gelatin Food Science. 14 Dec. 1998.

About 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