Freezing is an indispensable tool in modern cooking and eating. The biochemical processes that typically occur in meats cause decay, fat oxidation, and rancidity; the higher the temperature, the faster these reactions occur. Thus, we can largely thwart off these undesirable processes by keeping meat chilled. But tossing meat into the freezer rarely results in rainbows, sunshine, or perfect burger patties, because strangely enough we can also accelerate meat decay with cold. Freezer burn can take a beautiful filet mignon and turn its surface into a leathered, unappetizing slab.
Freezer burn is caused by water sublimation from ice crystals at the meat’s surface into the dry freezer air. Sublimation occurs when a solid substance undergoes a phase change and becomes a vapor without first passing through the liquid phase. The ice crystals on the meat surface sublimate, and leave behind tiny cavities. These tiny yet numerous cavities increase the surface area of the meat and expose more tissue to the air. This accelerates oxidation of fats, which causes the rancid flavors of old spoiled meat. We usually describe oxidized fats as simply tasting “off,” which is a vague term but seems apt if you’ve ever tasted lipids past their prime, perhaps by using shortening that has been in the pantry since you were a toddler.
Here, solid ice crystals directly vaporize without first passing through the liquid phase. Photo Credit: flickr/Marcus Ward
In addition to the surface area increase caused by sublimation, the freezing process itself lends itself to fat oxidation. When the liquid water in meats crystallize in the cold, the concentrations of oxidizing salts and trace metals in the tissues increases. Unfortunately, oxidation can occur over time even in wrapped and frozen meats. Some oxygen will inevitably remain in contact with the meat, unless we create a vacuum seal.
Once meat has been damaged by the cold, there’s no undoing the oxidation. So either we plan our meals so that meats are cooked immediately after purchase, or we learn to prevent the sublimation that ruins both our pork chops and our days. We simply need to keep water crystals inside the meat and keep oxygen out. Using a vacuum sealer is our best bet for avoiding freezer burn, but for cheapskates like me who won’t shell out the $30 for the sealing device, a water-impermeable plastic wrapped tightly around the meat works well enough for most home chefs.
Thus meat is sealed away happily in plastic, free from villainous oxygen. Photo credits: flickr/Mike
McGee, Harold. “Meats.” McGee on Food & Cooking: An Encyclopedia of Kitchen Science, History and Culture. London: Hodder & Stoughton, 2004. N. pag. Print.
“Sublimation.” The Columbia Electronic Encyclopedia. Columbia University Press, 2012. Web. 20 July 2015.
About the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.
Watch a barista at work and you will observe the art of preparing a perfect café au lait, cappuccino, macchiato, or mocha – all of which involve different quantities of steamed milk. Behind the artistic foam hearts and milk mustaches lies a science to steamed milk.
Students of UCLA’s SPINLab (Simulated Planetary Interiors Lab) team developed an app that allows you to “calculate the power output of your steamer” and predict the “steaming time for optimal milk temperature based on amount, type and starting temperature of your milk”. Samuel May of SPINlab explains the calculations the app takes into account that allows it to predict the temperature of milk at a given time. They show that the temperature increase of milk over time is linear, allowing them to make these predictions based on a Linear Heating Model.
But what exactly happens when you steam milk? Steaming involves introducing hot water vapor (T = 250-255 °F) into cold milk (T = 40 °F) until it reaches the ideal temperature for a “perfectly steamed latte.”
While the process sounds simple enough there are a host of variables that need to be considered. Most importantly, different milks require different amounts of steaming time. As SPINLab expert, Sam warned, too high a temperature can scald the milk: scalding kills bacteria and denatures enzymes; this inactivates the enzymes and causes curdling as denatured milk proteins clump together. Since different types of milk and dairy alternatives have different molecular compositions, this means they have different steaming temperatures. This difference all boils down to the composition of milk.
Figure 1. Milk broken down into its molecular constituents. Modified from Properties of Milk and Its Components. 
Milk is composed of three main components: of proteins, carbohydrates, and fat (Figure 1).
Milk is 3.3% total protein, including all nine essential amino acids; the protein content can be broken down into two main types, casein and serum. Serum, or whey proteins, contain the majority of the essential amino acids. Whey proteins can be coagulated by heat and denaturation of some of these proteins with heat; this gives cooked milk a distinct flavor. Caseins form spherical micelles that are dispersed in the water phase of milk . When steaming milk, the injected air bubbles disrupt the micelles. The protein molecules then encompass the air bubbles, protecting them from bursting and leading to the formation of foam. The take away: The different protein content of different milks consequently affects each milk’s ability to maintain that frothy foam decorating your latte . Whole milk results in a thicker, creamier foam and skim milk results in more foam and larger air bubbles, while almond milk is able to hold a light and long-lasting foam .
Table 1: Percent of protein in different types of milk and non-dairy alternative 
Lactose is the carbohydrate component of milk – a disaccharide composed of D-glucose and D-galactose. There are two forms of lactose present in an equilibrium mixture due to mutarotation, α-lactose and β-lactose. β-lactose is the more stable form, and also the sweeter form of the two . When you steam milk past a temperature of 100 °C, this causes a “browning reaction,” or the Maillard reaction, in which the lactose and milk proteins – mostly caseins – react to form what is know as an Amadori product . The colorless Amadori product is a molecular complex between the lysine residues of protein molecules and the lactose molecules. As the reaction continues with heating, the Amadori product can undergo dehydration and oxidation reactions, or rearrangements that lead to a loss of nutritional value and the formation of unappealing flavor compounds in milk that Sam warned could result from over-steaming.
The last main constituent of milk is the milkfat that exists as globules in the milk. Over 98% of milkfat is made up of fatty acids of different types, including saturated, monounsaturated, and polyunsaturated fatty acids. These fat molecules can also stabilize the formation of foam by surround the air and entrapping it in a bubble. While higher fat content leads to stable foam at temperatures below room temperature, milks with lower fat contents (like skim milk) are better at stabilizing foam at higher temperatures . This could be due to the reduced surface tension of the fat along the air bubble surface that is a result of an increase in fat percentage. Heating up these fat molecules not only affects foam texture; when heated or steamed, the fatty acids also participate in chemical reactions, such as oxidation reactions, that can give rise to an undesirable flavor .
For the lactose intolerant and fans of non-dairy alternatives, you may be wondering how lactose free options such as soy or almond milk compare. Their steaming temperatures differ mildly due to their distinct properties – for example, almond milk has a lower protein content (Figure 2). According to the experience and experimentation of expert baristas, certain brands of soy or almond milk can hold a foam better than others; the science underlying this phenomenon still remains to be determined.
Table 2: Ideal steaming temperatures for milk and non-dairy alternatives 
The moral of the story is that each component of milk contributes to its ability to froth and foam, and steaming influences each of these components. With this knowledge, you can wisely choose your milk at Starbucks depending upon your foaming desires, or simply download Sam’s app and perfectly steam your milk at home.
O’Mahony, F. Milk constituents. Rural dairy technology: Experiences in Ethiopia, Manual No.4; International Livestock Centre for Africa Dairy Technology Unit, 1988.
Christina Jayson is a recent UCLA Biochemistry graduate about to embark on her Ph.D. journey at Harvard.
00Grant Alkinhttps://sites.lifesci.ucla.edu/ibp-scienceandfoodnew/wp-content/uploads/sites/123/2016/09/newlogoSm-2-300x31.pngGrant Alkin2015-07-21 10:00:282015-07-21 10:00:28The Science of Steamed Milk: Understanding Your Latte Art
At UCLA, researchers reveal another benefit of yogurt: probiotics found in yogurt can help improve brain function. Learn more about the world that probiotics occupy in a podcast about the “messy mystery in the middle of us” over at Radiolab. Read more
00Grant Alkinhttps://sites.lifesci.ucla.edu/ibp-scienceandfoodnew/wp-content/uploads/sites/123/2016/09/newlogoSm-2-300x31.pngGrant Alkin2014-12-04 10:00:572014-12-04 10:00:57Gut Bacteria & Gut Rumblings
Featuring Dr. Dana Small, Chef Wylie Dufresne, & Peter Meehan
May 14, 2014
As part of our 2014 public lecture series, we explored the concept of taste from the perspectives of a scientist, a chef, and a food writer. Dr. Dana Small described how our brains respond to flavors. Chef Wylie Dufresne of Wd~50 presented his creative approach to generating surprising food flavors and textures. Peter Meehan shared his experiences with food and taste and how they have shaped his writing, both as a cookbook author and former writer for The New York Times.
Check out the highlights or watch the full lecture below
Wylie Dufresne on Science in the Kitchen and It’s Impact on WD~50
“Cooking is a lot of things and one of the things we discovered was that cooking is a science. There’s certainly some biology. There’s certainly some physics. There’s an awful lot of chemistry at play all the time when you’re cooking… One of the main reasons I opened up WD~50 … was to create a space where I could continue my culinary education, where my staff could continue their culinary education, and where you as a diner, if you so choose, could continue your culinary education.”
Wylie Dufresne on his Aerated Foie Gras
“How could we, using some very modern technology, walk the idea of a mousse down the road? … Part of the problem with a mousse is that it usually has a lot of stuff in it besides the main ingredient… So what we wanted to do was to figure out if we could create a mousse of foie gras, or if we could aerate foie gras without adding or taking too much away from the flavor.”
Peter Meehan on Developing Taste and Eating Everything
“The first step in developing the taste to become a restaurant critic: Eat … I tried to just each everything… the more I ate the more I understood about food and the more I could draw connections about one thing and another… You start to make these mental points on a map of where flavors are in relation to each other.”
Dr. Dana Small Defines Taste
“There’s molecules and ions in the foods that we eat and they bind to cells on these elongated taste receptors [tastebuds]. When enough binds, the cells get excited. They send a signal to the brain that the brain then interprets as a taste … Taste evolved to detect the presence of nutrients and toxics … You’re born knowing that you like sweet and dislike bitter … because you don’t want to have to learn that sweet is energy and bitter is toxin.”
Dr. Dana Small Defines Flavor and How It’s Different from Taste
“Flavor, on the other hand, preferences and liking for flavors is entirely learned. This has the advantage of allowing us to learn to like available energy sources and learn to avoid particular food items … The flavor allows us to identify a particular item that was associated with a particular consequence that we need to remember… whereas the taste provides just a signal about whether an energy source as in the case of sweet is present.”
Watch the Entire Lecture
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The Science of Sushi
Featuring Dr. Ole Mouritsen and Morihiro Onodera April 23, 2014
To kick off our 2014 public lecture series, Dr. Ole Mouritsen joined Chef Morihiro Onodera to satisfy our craving for sushi-related science. The duo explained everything from sushi’s early history to the starchy science of sushi rice. Watch the entire lecture or check out some of the shorter highlights below.
Ole Mouritsen on the history of sushi
“The history of sushi is really the history of preservation of food. . . . Throughout Asia, in particular in China and later in Japan, people discovered that you can ferment fish – that is, you can preserve fish – by taking fresh fish and putting it in layers of cooked rice. . . . After some time the fish changes texture, it changes taste, it changes odor, but it’s still edible and it’s nutritious. And maybe after half a year you could then pull out the fish and eat the fish. That is the original sushi.”
Ole Mouritsen on the science of rice
“If you look inside the rice, you have little [starch] granules that are only three to eight microns, or three t0 eight thousandths of a millimeter, big. . . . When you cook the rice, you add some water and the water is absorbed by the rice and [the granules] swell. And the real secret behind the sushi rice is that when they swell, these little grains are not supposed to break.”
Morihiro Onodera on examining the quality of sushi rice
“First what I do is I soak uncooked rice in water. . . . Sometime after 20 minutes it will start to break. . . . I take a sample to check to see if there are any cracks. . . . With good rice, which has less cracks or breaks, you’re able to feel the texture of each of the grains in your mouth, whereas with the lower quality rice you’re just going to get the stickiness [from the starch].”
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As the doors swung open, guests eagerly awaiting the final Science & Food lecture series were transported to a place nothing short of a Pie-Palooza. Twenty student teams stood confidently next to their baked confection and explained to the judges how they employed the scientific method to creatively reimagine the art of baking the perfect pie. Some developed aqueous solutions to modify the flakiness of their pie crusts while others sought to improve filling texture by altering pH levels and used techniques such as microscopy to measure their results. Whatever their approach, the students proved that a little bit of science goes a long way in mastering the craft of pie baking.
Dr. Paul Barber (Associate Professor, UCLA) and Dave Arnold carefully evaluate the student pie presentations
Nicole Rucker (Pastry Chef, Gjelina Take Away) and Jonathan Gold (Food Critic, LA Times) partner up as special guest judges
Lena Kwak and Dr. Rachelle Crosbie-Watson (Associate Professor, UCLA) take a closer look at student posters
After the large-scale pie tasting, guest speakers, Lena Kwak and Dave Arnold, took the stage to share their insight on innovation in the culinary laboratory and emphasized how unforeseen mishaps often lead to novel discoveries. Co-Founder and President of Cup4Cup, Kwak discussed how her breakthrough formulation of gluten-free flour was a by-product of her fearlessness to try new techniques and make mistakes in the kitchen. Founder of the Museum of Food and Drink (MOFAD) and Owner of Booker & Dax, Arnold described how curiosity and relentless dedication to experimentation led to the development of many of his out-of-the-box culinary gadgets. Case in point: the Searzall, one of his latest inventions designed for hand-held blowtorches to evenly apply high temperature heat to sear foods while avoiding the remnants of unpleasant aromatics. He also invoked the audience to participate in an experiment where he challenged everyone to digest gymnemic acid, which dulls our sensory perception of sweetness. This exercise was designed to help guests unlock and appreciate the other factors (such as texture) that contribute to our understanding of taste.
Kwak addresses the audience’s questions and reveals some of ingredients in her gluten-free flour
Arnold explains and demonstrates the evolutionary process involved in developing the Searzall
Gymnemic acid, a sweetness inhibitor, made this bag of sweets taste completely bland
Finally, the panel of special guest judges shared with the audience their favorite pies from the student entries and awarded the students with prizes for the “Most Creative Pie”, “Most Qualified to Enter a Real Pie Contest”, “Best Scientific Pie”, “The People’s Choice Pie”, and “Best Overall Pie”.
Tom Folker and Eric Hirshfield-Yamanishi take home the “Most Qualified to Enter a Real Pie Contest” prize
Folker and Hirshfield-Yamanishi explored the effect alcohol, specifically Fireball whiskey, had on the overall flakiness of their pie crust and produced a pie the judges thought was worthy of a professional pie contest.
The “Most Creative Pie” went to Ying Zhi Lim and Jen So for their imaginative apple pie
These creative young women, Lim and So, took the competition to the next level by presenting a deconstructed, rosemary-infused apple pie topped with a “reverse spherified” lemon zest cream cheese sauce to a create a harmoniously balanced and flavorful treat.
Christina Chung, Tori Schmitt, and Elliot Cheung impressed the judges and won the “Best Scientific Pie” award
Chung, Schmitt, and Cheung added different combinations of liquids to generate their pie crust and recorded the amount of force required to alter the elasticity of the baked crust. Ultimately, the incorporation of beer into their pie crust recipe significantly altered texture as measured and quantified by the elastic modulus.
Naqvi and Upkins-Scott of team Apple Queens took different varieties of apples, including Granny Smith, Red Delicious, Pink Lady, and Fiji, to produce a crumble top pie that garnered praise from both the audience and the judges.
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Chef Morihiro Onodera trained as a sushi chef in Tokyo, and at seminal Los Angeles restaurants including Katsu, R-23, Matsuhisa, and Takao as well as Hatsuhana in NY. By the time he opened his first restaurant, Mori Sushi in Los Angeles, he was preparing many of the same handmade ingredients, harvesting his own locally grown rice and creating handmade pottery to be used in the restaurant. After selling Mori Sushi in 2011, Mori began creating handmade pottery for several Michelin Guide restaurants in Los Angeles and established a partnership with rice farmer, Ichiro Tamaki. Tamaki farms in Uruguay will harvest its first crop in May of 2013 and will be available for distribution world-wide.
The desire to want to eat and taste delicious food.
The coolest example of science in your food?
My basic approach to cooking is to think about the natural ingredients and the climate (seasons) of its origin, ingredients that are kind to the body and to earth—a very simple-minded attempt with natural science at its core.
The food you find most fascinating?
I’m always seeking the true flavor of a given ingredient—that’s what fascinates me.
What scientific concept–food related or otherwise–do you find most fascinating?
Your best example of a food that is better because of science?
Konbu and natural salt.
How do you think science will impact your world of food in the next 5 years?
It will be interesting to see how the true flavors of ingredients change over time—how natural science will affect that change. Simultaneously, I will continue my studies in discovering and knowing what’s kind for the human body and our earth.
One kitchen tool you could not live without?
Rice cooker, including donabe (Japanese clay pot).
Five things most likely to be found in your fridge?
Fresh local vegetables, miso, umeboshi (pickled plum), homemade yuzu kosho (pepper), and leftover cooked brown rice. Outside of the fridge: dry goods, salted bran (used for pickling), rice, oil (sesame and olive), salt, konbu.
Your all-time favorite ingredient?
Book series by Rosanjin (Kitaoji Rosanjin, Japanese artist and epicure).
Your standard breakfast?
Black tea (straight). Seasonal, local fruits. Bread or hot rice cereal. Sometimes eggs (steamed) cooked with sautéed spinach.
This week marks the beginning of UCLA’s Spring Quarter, which can only mean one thing… It’s time for the Science & Food undergraduate course! We have a stellar lineup of chefs and farmers slated for our third annual offering of Science & Food: The Physical and Molecular Origins of What We Eat. Although the course is only open to current UCLA students, we will be posting highlights from the course right here on the blog. Until then, check out this year’s course speakers and brush up on some of the great science we’ve learned in past courses.
Featuring Alice Waters, Wendy Slusser, and David Binkle April 25, 2013
At this enlightening evening of food education, Chef Alice Waters shared valuable insights into food culture and her work with the Edible Schoolyard Project. Chef David Binkle and Dr. Wendy Slusser then provided an informative discussion on initiating change in how we eat through school lunches and healthy campuses. Watch the entire lecture or check out some of the shorter highlights below.
Alice Waters on fast food culture and slow food values
“I can’t tell you how many times I’ve been accused of being a Farmers market philanthropist because I believe in paying people for the true cost of their food and their products. And people say that I’m artificially driving up the prices of food in the markets. And I say, it’s the discounted prices that are artificial. I feel that it’s my responsibility to pay for the true cost of things, if I can.”
David Binkle on LAUSD’s school lunch program
“In our school district more than 80% of our children qualify from circumstances of poverty. And that is a real challenge for our children just to get a good, healthy, nutritious meal every day. So our job is to really provide that healthy, nutritious option to the children.”
Wendy Slusser on UCLA’s Healthy Campus Initiative
“UCLA serves as a leader in Los Angeles and around the world, and by prioritizing health in its broadest definition we are signaling that we value living well. And so what does the Healthy Campus Initiative focus on? Make the healthy choice the easy choice, so that we can live well, eat well, breathe well, move well, be well, and mind well.”
Chef Alex Atala is famous for scouring the Amazon for interesting new ingredients. At his Science & Food lecture, Primitive X Modern, Chef Atala shared some of his innovative creations with everyone in the audience. One ingredient in particular really challenged our perception of what we consider to be edible: Amazonian ants!
While we don’t expect insects to show up in American grocery stores any time soon, it is estimated that at least 2 billion people worldwide already eats insects on a regular basis . Here are 6 things you might not know about eating insects:
“What is honey? The excrement of an insect. If you actually consciously think about what honey is, it’ll disgust you. But we are familiar with it, we have an interpretation of it being sweet. Hell, in English we’ll say, ‘Honey, I love you.’”
-Alex Atala, Eater 2011
Food and Agriculture Organization of the United Nations (2013) Edible insects: Future prospects for food and feed security. http://www.fao.org/docrep/018/i3253e/i3253e00.htm
Editor’s note: The original post stated that shellac and cochineal come from beetles when, in fact, they come from insects in the “true bug” order Hemiptera. Thanks to our astute readers for catching this mistake! The post has now been updated (10-24-2013 9:55 a.m. PST)
About the author: Liz Roth-Johnson is a Ph.D. candidate in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.
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