Physics | Duke Research Blog

Chocolate’s crisp crack comes from chemistry

March 28th, 2013

By Ashley Yeager

This is the final post in a four-part, monthly series that gives readers recipes to try in their kitchens and learn a little chemistry and physics along the way. Read the first post here and the second one here and the third one here.

This bunny must have been made from quality chocolate. His ears are already gone. Credit: Waponi, Flickr.

When you snap off and savor the ears of a chocolate bunny this Sunday, say a quick thanks to science.

“The essence of science is to make good chocolate,” said Patrick Charbonneau, a professor of chemistry and physics at Duke.

He explained that cocoa butter, one of the main ingredients in chocolate, can harden into six different types of crystals. All six types are made of the same molecules. But, at the microscopic level, the types have distinct molecular arrangements, which lead to differences in the crystals that form.

“The problem with chocolate is that only two of these types have good texture when eaten,” Charbonneau told students in the Chemistry and Physics of Cooking.

He teaches the freshman seminar with chef Justine de Valicourt and chemistry graduate students Mary Jane Simpson and Keely Glass.

During class, students looked at and tasted chocolate containing only the good-tasting crystal types and some that also contained the less favorable ones. The first had that signature sheen and snap of quality chocolate and melted evenly when left on the tongue. The latter pieces were dull, melted with the slightest touch and left a sandy texture on the tongue.

The demonstration showed that the different types of chocolate crystals melt at different temperatures. By carefully controlling the chocolate as it cools, chocolate-makers can create mixtures of only the favorable crystal types.

The process, called tempering, takes chocolate through a series of heating and cooling steps. The initial cooling step forms many of the chocolate crystal types, including the dull, unfavorable ones. Warming the mixture a little — to about 31°C (87°F) — melts the unfavorable crystals but not the best-tasting ones.

As the mixture cools again, the remaining, favorable crystals “seed” the chocolate so that good-tasting crystals form preferentially throughout, ensuring good chocolate structure and taste.

Students got a chance to test the science in lab later that evening, and judging by the number of mouths (and faces) covered with chocolate, it’s safe to say the science was successful.

If you’re looking to try it out — or save a poor bunny’s ears — here’s the recipe.

Tempering chocolate:

Materials:
1 small, microwave safe bowl
1 big bowl
1 spatula
2 scraper spatulas
1 chocolate mold
parchment paper
cooking thermometer

Ingredients:
250 g Dark Chocolate or 250 g Milk Chocolate (about 1 1/3 cups)

Filling:
60g white chocolate (about 1/4 cup)
60g yogurt (a little less than 1/4 cup)

Instructions:

1. Place milk or dark chocolate in the small bowl.
2. Heat the bowl in 30-second intervals in a microwave (stirring after each) until the chocolate is melted. Note: The milk chocolate should take about 1.5 minutes and the dark chocolate about 2 minutes to melt.
3. Once heated, pour half the liquid chocolate onto a clean marble or stone counter. The chocolate puddle should be the size of a medium pancake. (Note: If there is not stone or marble surface, another technique is to melt less chocolate and then add good tempered chocolate in it to lower the temperature.)
4. Spread the pancake portion out in ribbons using the scraper spatula. Bring the chocolate back together into a mound repeatedly for 5 minutes, until it starts to solidify.
5. Put the chocolate back in the original heating bowl. Adding the cooler chocolate will cool the rest of the liquid to the right temperature.
6. Mix the cold and hot chocolate.
7. Check the temperature of the chocolate. (Dark: 31-32°C/88-89.5°F; Milk: 29-30°C/84-86°F).
8. Dip the parchment paper in the mixture of the “hot” and “cold” chocolate. If it cools on the parchment paper and is uniform and shiny, then it’s ready.
9. Pour chocolate into mold.
10. To make stuffed chocolate candies, flip the mold to empty excess chocolate.
11. Turn it back, scrap the excess of chocolate off the surface. Let the thin layer of chocolate in the mold crystallize.
11. Melt white chocolate. Mix it with yogurt. Cool to room temperature.
12. Add filling to 2/3 of the mold cavities, and then pour more tempered chocolate on top.
13. Level the chocolate with a scraper and scrape off excess.
14. Let it rest for few minutes at 20°C (68°F) or put it in the fridge.
15. Pop candies from mold and enjoy.

Local high-schoolers analyze real LHC data at Duke

March 18th, 2013

By Ashley Yeager

Duke physicist Mark Kruse explains a few finer points of analyzing LHC data to two NCSSM students. Credit: Ashley Yeager, Duke.

Duke physicist Mark Kruse explains finer points of analyzing LHC data to two NCSSM students. Credit: Ashley Yeager, Duke.

Thin, blue lines spider across the computer screen. With a click on one, a solid blue peak on a bar graph pops up. A click on the other line makes a similar graph. Looking at them closely, two high-schoolers decide if they could be signatures of a particle called a Z-boson.

The girls — physics students from the North Carolina School of Science and Mathematics (NCSSM) — log their analysis of the lines and move on to another set. They aren’t getting too excited about their possible Z-boson discovery yet because they still have 48 other sets of lines, or events, to analyze.

Once they’ve worked through all the events, they’ll know if what they’ve seen could be due to a Z-boson decaying into pairs of electrons or muons.

“This exercise isn’t that much different than what scientists do to look for Higgs bosons,” said Duke physicist Mark Kruse, adding that the exercise is a good illustration of the particle-hunting process. “It shows you that you can’t just look at a single event and say ‘that’s a Higgs boson’.”

Kruse shared this insight with the two girls and a dozen other NCSSM high-schoolers during a Large Hadron Collider (LHC) Masterclass held at Duke on March 16. The European Particle Physics Outreach Group runs the masterclasses annually with help from university professors such as Kruse. This was the first time Duke hosted the program for local students.

During the day, they got an introduction to particle physics and research at the LHC and an overview of ATLAS, the experiment Kruse and his collaborators use to search for Higgs bosons and other particles. Then, after a tour of Duke’s Free Electron Laser facility and a pizza lunch, the high-schoolers got their hands on real LHC data.

NCSSM students work on LHC data to find hints of Z-bosons. Credit: Ashley Yeager, Duke

They were looking mainly for events that showed possible remnants of a Z-boson. But a few Higgs-like candidates were thrown in too, which excited the students, Kruse and his two graduate students David Bjergaard and Kevin Finelli. The group may have even found a Higgs candidate in one of the first event analyses they looked at during the day.

But, as with all discoveries, they had to take a closer look at their analyses and share their work with others. The group closed the day with a videoconference with high-schoolers in Medellin, Colombia who also went through an LHC masterclass at the same time.

“This was an impressive group. They asked a lot of great questions, sparking some incredible discussion,” Kruse said. The questions — like, does anything make up a quark — are ones other audiences are perhaps too intimidated to ask because they might think it’s a silly question, he said. But it’s these questions that really get everyone thinking about the fundamentals of physics and how much scientists still don’t know, including if quarks can break down into anything smaller. This is in fact one of the many questions LHC scientists are trying to answer.

Based on the success of the class, he is now thinking of running it again for physics students from other area high schools and possibly adapting it for journalists and policymakers. The goal is to illustrate to a wider audience the “gradual, cumulative nature of discovery” at the LHC, he said.

CERN particle ‘a’ Higgs, but not ‘the’ Higgs yet

March 14th, 2013

By Ashley Yeager

This artist’s impression shows a proton-proton collision producing a pair of gamma rays, in yellow, in the ATLAS detector at LHC. Credit: CERN.

Scientists say the particle they described in July 2012 is looking more like a Higgs boson. But they can’t yet say much more than that.

Speaking at the Moriond meeting in Italy, researchers using the Large Hadron Collider near Geneva explained their latest analyses show the new particle’s “spin” matches theorists’ predictions for that feature of the Higgs boson.

Physicists want to find a Higgs boson because it would give them clues to the mechanism that gives mass to elementary particles. Finding one specific flavor of the particle would also complete the Standard Model of particle physics, a system that explains how the smallest particles and forces interact to run the universe.

“The updates show this particle is Standard Model-like, but my personal feeling is we can’t yet call it ‘the’ Standard-Model Higgs,” says Duke physicist Mark Kruse who works on one of the Higgs-hunting experiments at CERN. “For one, we believe the Standard Model is wrong.”

The model, he says, does not predict a candidate for dark matter, a form of mass that scientists can’t yet describe. And, he adds, even if the particle’s characteristics, such as spin, match those of the Standard-Model Higgs, scientists can’t yet rule out other theories that also contain Higgs particles with properties similar to the Standard-Model Higgs.

“All we can really say is that this particle is ‘a’ Higgs boson, but not necessarily ‘the’ Standard-Model Higgs,” Kruse says. “We have a lot more to understand and a lot of future research to acquire that understanding.”

Meat Glue — True to its Name

March 8th, 2013

By Ashley Yeager

This is the third post in a four-part, monthly series that gives readers recipes to try in their kitchens and learn a little chemistry and physics along the way. Read the first post here and the second one here.

Students grab chunks of a fish “checkerboard” made from salmon and flounder cubes. Credit: Ashley Yeager, Duke.

Braided steak and checkerboard fish may sound exotic. But, freshmen in the Chemistry and Physics of Cooking had no fear fingering the meaty masterpieces into their mouths.

The students made this food art – one literally a braid of three steak strips and the other a combination of salmon and flounder cubes – using a molecule called transglutaminase, also known as meat glue.

In 2012, the media roasted meat glue’s reputation, branding it a dirty little secret meat vendors use to stick together cheap cuts of beef, lamb, chicken or fish and then sell as premium cuts.

“In this class, we’re not using the molecule to be dishonest. We’re using it to be creative,” said physical chemist Patrick Charbonneau, who leads the freshman seminar along with chef Justine de Valicourt and teaching fellows Mary Jane Simpson and Keely Glass.

During a lecture, Glass explained how meat glue — an enzyme that speeds chemical reactions — forms covalent bonds between some of the amino acids that make up the proteins in meat and meat substitutes. With just a sprinkle of the enzyme, which comes in a powder form, chefs can then weave together beef cuts, form game-piece patterns from fish or even bind beans, seeds and other ingredients into a veggie burger that doesn’t crumble after the first bite.

“Meat glue is like a lot of modern ingredients. It comes from industry, and you can use it to make industrial food,” like chicken nuggets, de Valicourt said. “But when you master it, you can use it in a very creative and delicious way.”

Chefs often use the fundamentals of chemistry and physics to shape other foods, such as chocolate. “We’re doing the same to shape meat,” Charbonneau said, explaining that the students used transglutaminase in lab to create beautiful, and delicious, combinations of meat far superior to chicken nuggets and other industrial food typically made with the enzyme.

To make your own meat masterpieces, try the following recipe:

Materials:

1 long sheet of plastic wrap OR a bowl
1 cutting board
1 knife
2 latex gloves for each person
1 mask for each person
1 meat grinder (optional)
1-3 gallon-sized Ziploc bags
1 scale

Ingredients:

1 portion fish, chicken, beef OR vegetarian protein (ie black beans and sunflower seeds)
10 g meat glue powder (available online here)

Instructions:

Gluing meat chucks together –

1. Choose meats
2. Place meat on plastic wrap
3. Choose meat pattern – braid or stack
4. Season meat with salt and pepper
5. Put on gloves and mask and measure 10 g of meat glue using the scale
6. Sprinkle meat glue on sides of meat you want to connect
7. Fold meat into desired pattern
8. Place meat in Ziploc bag
9. Refrigerate for 6 hours
10. Cook meat as you would any other time

Making meat patties –

1. Choose meats, grind in meat grinder, and mix in a bowl (Or, buy ground meat and mix)
2. Season meat with salt and pepper
3. Put on gloves and mask, then measure 10 g of meat glue using the scale
4. Add meat glue to meat and knead until fully mixed
5. Separate into two portions (or more for patties) and seal each in a Ziploc bag
6. Roll with rolling pin, if desired
7. Refrigerate for 6 hours
8. Cook meat as you would any other time

Diffusion a la Chocolate Lava Cake

February 21st, 2013

By Ashley Yeager

Note: This is the second post in a four-part, monthly series that will give readers recipes to try in their kitchen and learn a little chemistry and physics along the way. Read the first post here.

Making chocolate lava cakes demonstrates the diffusion of heat. Credit: Ashley Yeager, Duke.

Between bites of hot lava cake and vanilla ice cream, freshmen taking Chemistry and Physics of Cooking talk about diffusion. Their conversation isn’t so esoteric that an outsider wouldn’t understand.

Instead, it’s a simple chat about how long to cook a cake based on how heat moves.

Understanding diffusion is a way to make sense of cooking times, says chemistry and physics professor Patrick Charbonneau, who is leading the class along with chef Justine de Valicourt.

Diffusion of matter is how particles in a liquid, gas or solid intermingle and move from a region of higher concentration to one of lower concentration.

Heat diffusion describes how hot particles warm up cooler particles around them, which allows the inside of a dish to cook, even though only the outside is heated.

Before turning his students loose in a kitchen in Smith Warehouse to eat a product of this process, Charbonneau and his teaching fellows had the group work through the equations that describe diffusion.

“Solving the diffusion equations of heat gives you a first estimate of how long to bake a cake or cook a turkey,” Charbonneau says. The cooking time for lava cake is especially critical in order to get the outside it to bake, while the inside remains gooey, de Valicourt adds.

In class, the students calculated that to make a muffin-sized lava cake with ingredients at room temperature in an oven at 400°F (204°C) would take about 10 minutes. In the lab, they found that the calculation was fairly accurate, but for a more exact estimate of cooking time, they needed to factor in the temperature of melted chocolate chips in their recipe.

“Still, with the cooking time being not so mysterious, it’s one fewer thing left to chance,” Charbonneau says, adding, “then you can be more creative with the recipe in other ways.”

He and de Valicourt, who have partnered with the Alicia Foundation to offer the Chemistry and Physics of Cooking class, have provided the following recipe for experimenting with diffusion and hot lava cake.

Hot Lava Cake –

Ingredients:
60g (1/3 c) dark chocolate chips
60 g (1/2 stick) butter
60 g (1/4 c) sugar
3 eggs (or 2 egg and 45mL (3tbs) coconut milk)
30 g (1/4 c) flour
small pinch salt
Non-stick cooking spray

Materials:
1 bowl (bain-marie)*
4 ramekin dishes or 1 muffin tin
2 medium bowls
1 scale (if weighing ingredients)
1 sieve
1 cooking thermometer (optional)

* You can make a bain-marie by placing a bowl over a saucepan of simmering water.

Instructions:

1. Preheat the oven to 400°F/204°C.
2. Melt chocolate and butter on bain-marie. Stir. Do not boil the water or the chocolate could burn.
3. Combine eggs and sugar (and coconut milk) in a medium bowl and whisk until bubbly.
4. Combine flour and salt in another bowl and pass it through the sieve.
5. With one person whisking and another pouring, slowly add the chocolate mixture to the egg mixture.
6. Add the flour and salt to the wet ingredients and whisk well.
7. Spray ramekins or muffin tin with non-stick cooking spray.
8. Fill the ramekins or muffin tin a little more than halfway full.
9. Place the ramekins or tin in the oven on the middle rack.
10. Bake until the cakes start growing. The interior of the lava cake should be around 158-176°F/70-80°C and the outside around 203-212°F/95-100°C – ie until the edges of the cake are set, but the center is still a liquid – about 7 to 10 minutes (less for smaller cakes).

Close Encounters of the Twitter Kind

January 30th, 2013

By Ashley Yeager

Astrophysicist Katie Mack and other researchers are starting to join Twitter to do better science. Image courtesy of: mediabistro.com

Before launching into dark matter’s effects on particle physics in the early universe, astrophysicist Katie Mack of the University of Melbourne in Australia took a little detour Wednesday to talk about Twitter.

The social media tool is helping her “do better science and learn about new science,” she said during her Jan. 30 seminar at Duke.

The talk materialized from a tweet she had posted a few days ago about attending ScienceOnline, an annual, Raleigh-based conference for scientists and communicators talking and writing about science on the Internet.

Duke physicist Mark Kruse, who joined Twitter in October after the 2012 Council for the Advancement of Science Writers meeting, saw Mack’s tweet about coming to the Triangle and then contacted her to see if she would like to speak about her research.

She said yes, obviously, and explained during her talk that the invitation, as well as the other networking she has done on Twitter, got her to thinking about why all physicists (and scientists) should use the site.

@AstroKatie shares her top reasons scientists should be on Twitter. Credit: Katie Mack, U. of Melbourne.

Here is a paraphrased list of her top five reasons:

1. You can see what scientific breakthroughs people are getting excited about.
2. You can keep track of science discoveries outside of your field.
3. You can share your work with a broader audience.
4. You can connect with other scientists in and outside your field, building your professional network.
5. You can connect and share your work with the public.

Clearly Mack’s invitation to speak at Duke illustrates her third point about Twitter. Now, she said, she looks forward to attending her first ScienceOnline meeting to build on those points and learn new ways of using the tool to connect with other scientists and science enthusiasts.

You can follow Mack at @astrokatie, Kruse at @markckruse and ScienceOnline at @ScienceOnline (or #scio13) if you’re already on Twitter.

And, if you’re a Duke researcher not yet on Twitter but want to be, check it out here, then contact the university’s news office if you’ve got questions.

Cooking up chemistry with candy

January 23rd, 2013

By Ashley Yeager

Note: This is the first in a four-part, monthly series that will give readers recipes that they can try in their kitchen and also learn a little chemistry and physics along the way.

Making sucre à la crème (left) and soft toffee (right) illustrates the fundamental principles of changing a liquid to a solid. Credit: Ashley Yeager, Duke.

A dozen freshmen pull on pieces of fresh, soft toffee, popping the candy into their mouths and licking it from their teeth as chef Justine de Valicourt talks about making the treats in a tiny kitchen on the second floor of Smith Warehouse.

Eating toffee and other sweets doesn’t usually spark a discussion about chemistry. But, as the students learn, the core of the eating experience is entirely about chemistry and some physics too, says professor Patrick Charbonneau.

He is leading a freshman seminar, called the Chemistry and Physics of Cooking, and in this particular class, he, de Valicourt and a team of teaching assistants work with the students to explore phase transitions – such as the change of liquid water to ice – by making two traditional Québécois desserts, sucre à la crème and soft toffee.

Both desserts have the same ingredients — maple syrup, butter and cooking cream. But, the experience of eating them is entirely different. One, the toffee, is stretchy, chewy and sticky, while the other, the sucre à la crème, is more crumbly and smooth.

The way the sugar molecules in solution cool down into a solid structure is what determines the final texture of a candy or chocolate, Charbonneau says.

During the lab, the students cool one mixture of syrup, butter and cream quickly and then whisk it. The stirring motion forces the sugar molecules to bump into each other, creating seeds of crystallization, which continue to grow and eventually clump together to give the sucre à la crème its solid, crumbly texture.

The students mix and heat the ingredients, then let them cool slowly, leaving the candy to set for at least three hours. Not whisked or stirred, it solidifies without forming too many large crystals, giving it a glassier appearance and a stickier, chewy texture, a signature feature of toffee.

Making these candies is pretty basic, easy enough that anyone could try it in a home kitchen, Charbonneau says, adding that he and de Valicourt have provided the recipes as a way to reach beyond the classroom and give more than just their students an introduction to cooking and, of course, the chemistry behind it too.

Sucre à la crème –

Ingredients:
1 can of maple syrup (540mL)
45 ml (3 tbsp.) of butter (plus some to grease the mold)
250 ml (1 cup) of cooking cream 35%

Materials:
1 medium saucepan
1 candy thermometer
1 wooden spoon
1 square mold
1 whisk
1 bucket of cold water

Instructions:

1. Put all ingredients in the saucepan. Stir.
2. Heat on the stove to 118°C (244°F) – 120°C (248°F). Be careful not to touch the bottom of the pan with the thermometer, which will give an incorrect reading.
3. Put the saucepan in the bucket of cold water and let the mixture cool down to 55°C (131°F) – 60°C (140°F) in the center. Do not stir the mixture.
4. Once cooled in the water, whisk the mixture to make a creamy pale paste. Pour in the mold and cut it before it gets too hard.
5. Let it rest 30 min in the fridge.

Soft toffee –

Ingredients:
1 can of maple syrup (540mL)
45 ml (3 tbsp.) of butter (plus some to grease the mold)
250 ml of cooking cream 35%

Materials:
1 medium saucepan
1 candy thermometer
1 wooden spoon
1 square mold

Instructions:
1. Put all ingredients in the saucepan. Stir.
2. Heat on the stove to 118°C (244°F) – 120°C (248°F). Be careful not to touch the bottom of the pan with the thermometer, which will give an incorrect reading.
3. Pour into the greased mold, let it cool down slowly, without disturbing it for 3-8 hours.

Higgs Hunters Seeing Double

December 13th, 2012

By Ashley Yeager

An stuffed animal artist’s conception of the Higgs boson. Credit: The Particle Zoo.

Scientists searching for the Higgs boson on the ATLAS experiment at the Large Hadron Collider near Geneva are reporting small discrepancies from the two main channels they use to look for the particle.

With these channels – the decay of a Higgs to two light particles (photons) or to two Z bosons – the scientists determined the mass of the Higgs-like particle to be roughly 125 GeV, about 125 times the mass of the proton.

They announced complimentary results from both channels in July 2012, and since then have been crunching more data to support the findings. The scientists gave updates on their work Dec. 13 at CERN.

“It’s turned out that for ATLAS the Zed-Zed channel and gamma-gamma channel differ quite a bit, by about 3 GeV, for the respective masses of the Higgs particle from which they decay,” says Duke physicist Mark Kruse, who is analyzing data from the ATLAS experiment. “It doesn’t sound like much, but the probability they could differ by this much or more is only about 0.5 percent.”

“This is probably not a big deal,” he says, noting that the new results explain why the ATLAS team was not ready to report the separate mass measurements at the November 2012 Hadron Collider Physics Symposium in Kyoto, Japan.

Kruse says there could be several reasons for the discrepancy. It could just be a statistical fluke. Or, there could be a subtle problem with one or both of the measurements. “There is a lot that goes into these analyses and it is not always possible at this stage to be absolutely certain every detail has been done perfectly,” Kruse says.

The more dramatic scenario is that these results could be due to two different Higgs-like particles.

Kruse, however, thinks the two Higgs-like particle answer is highly unlikely, especially if scientists using the CMS experiment at LHC do not report the same discrepancy. CMS scientists have not yet released their new “two photon” result.

The ATLAS result is most likely due to a statistical fluctuation. Right now, though, the team has only crunched about half the data from the collisions. Of course, scientists will only know more once they have analyzed the full ATLAS dataset a couple of months from now, Kruse adds, suggesting that there is still the possibly for more Higgs mania to come.