Holiday How-to: Chocolate Leaves

My mom was a chemistry and home-ec teacher, so I grew up in a home where ingredients were carefully measured and food items were attractively arranged. While I got to help out in the kitchen as much as I wanted, I always liked being in the kitchen around the holidays. There were always new tricks or special touches added to dishes and along with these came short science lessons on why we were doing things that particular way.

One of my favorite things to help with in the kitchen were chocolate leaves. When done correctly, these are perfect little molds of the living leaf, just like the perfect molds and casts in the Morian Hall of Paleontology.

A chocolate leaf is made by smearing melted chocolate onto a leaf and putting it into the fridge to harden. Sounds easy, right? It is pretty easy. Read on!


Activity: Chocolate Leaves


Leaves (*See note in step 1.)

Chocolate candy melts

Parchment or wax paper

A cookie sheet or plate for your leaves to rest on as they cool


1. Pick your leaves. I like to use slightly waxy leaves so you don’t have to worry about fuzzy bits in your chocolate. NOTE: Learn about the plant you are picking leaves from before you decide to use them. Many household plants are decorative but poisonous.  Oleander is a great example of a plant that is pretty but poisonous. If you hate botany or don’t know about the Internet, getting pre-packaged basil or mint from the grocery store is a safe way to go. These leaves will be a little less firm, so you will need to be more careful with them.

2. Don’t pick leaves from poisonous plants. Seriously.

3. Wash your leaves with soap and water, rinse them thoroughly and then dry them completely. The chocolate won’t stick to wet leaves, so don’t rush this step. You will only be frustrated.

4. Put wax or parchment paper on a cookie sheet or plate. You want this to be something that will fit in the fridge with no problems.

5. Get out your candy melts. The melts come in a hundred colors. We are using chocolate colored ones in this tutorial. There will be instructions on the package on how to melt the specific brand of melts you purchased. In general, you will put the melts in a microwave safe bowl and microwave them a few seconds at a time stirring as you go. Don’t overheat the melts. They get gross and there is no coming back from that.

6. When you have everything melted and creamy, hold the leaf by its stem. I like pinching it between my thumb and index finger and then using my middle and ring finger to support the leaf. Do what feels comfortable to you.

7. Dip your stirring spoon into the chocolate. Use the BACK of the spoon to spread the chocolate on the leaf. Make sure the chocolate is thick enough that it won’t break when you try to peel it. Place the leaves on the parchment as you work, and don’t let them touch.


8. The side of the leaf you use is up to you. If you are using mint and you put the chocolate on the back of the leaf, you will have some crazy patterns.  If you want something more subtle, use the front of the leaf. Coat the leaf almost to the edges. If you go too far, you will get ugly edges that are hard to peel. But don’t worry! Those leaves are the best to eat.

9. Put the tray of leaves in the fridge and wait a few minutes.


10. When the chocolate is set, peel the leave off the chocolate. You should have a perfect little mold of your original leaf. This may take a little practice. Work quickly as you have something designed to melt with heat in your hot little hands.

11. Done! You can store the leaves in the fridge until you are ready to use them. If the leaves got soft when you were working with them, put them back in the fridge to firm them up. Once they are firm, you can toss them in a plastic container.


Okay! So what’s the science here?

The word “chocolate” comes from the Nahuatl word Xocolatl for “bitter water,” referring to its original incarnation as a hot, spiced beverage in the Mayan and Aztec traditions. Traditionally, chocolate is a mixture of cacao powder, cocoa butter, and a sweetener. To make chocolate palatable and stable, we now mix milk solids, added flavors, modifiers, and preservatives.

Those candy melts? NOT CHOCOLATE! In this example, they are sort of chocolate colored, so they have that going for them, but they also come in a bunch of colors that are not known to nature so… not chocolate. They are mostly made of sugar and vegetable fats – not cocoa butter – and depending on the brand, they may throw in a little wax for better melting. Mmmmm… wax.

The advantage to the melts over the regular chocolate is that they do have the wax and the vegetable oil in them, which makes melting easier since the chocolate doesn’t need to be tempered. It hardens pretty quickly and sticks to whatever you dip in it, so it makes a great coating for cake pops or whatever crazy things show up on Pinterest this month.

Want to get super nerdy about your chocolate?  (I assume you do…) MIT has these tidbits available.

What’s in typical chocolate?

  • 10-20% cacao
  • 8-16% milk solids
  • 32-60% sugar
  • 10-20% cocoa butter
  • 2% theobromine and polyphenols

Cocoa Butter Chemistry

Fats and oils are organic molecules made up of three fatty acids chemically linked by an ester bond to glycerol. Fats are solid at room temperature, while oils are liquid.

Cocoa butter fats are made up predominantly by three major fatty acid molecules: Palmitic Acid, Stearic acid, and Oleic acid.

Oleic acid is unsaturated (has a double bond on its carbon chain), making it kinked and unable to pack well with other molecules. Because of this, a greater portion of oleic acid in the fat results in a lower melting temperature for the cocoa butter.

Chocolate makers can adjust the amounts of each fatty acid to produce a chocolate that melts only in the mouth, giving it a superior quality.

Tempering chocolate

The cocoa butter in chocolate can have several different crystal structures (three-dimensional patterns in which the fat molecules pack). There are six known chocolate crystal forms, or polymorphs. You can obtain each form by varying the fatty acid ratios and the temperature at which the chocolate is tempered (cooled).

Only a few of the polymorphs are considered good for gourmet chocolate because they give the right blend of snap (when you bite into the chocolate) and melting (when it warms up in your mouth). Melting is especially important because it controls how well the chocolate disperses and releases flavor onto your tongue.

Whether you will be constructing culinary masterpieces this fall or sitting back and enjoying the kitchen creations of others, we hope you have a happy holiday with you and yours!  (And when you’ve had a little too much togetherness, we will be open on Friday…)

Amazon Scavenger Hunt: a Fun Way to Explore Rainforest Sustainability

Recently my daughter and I were making cookies when she asked me, “Where do chocolate chips come from?”

I considered the glib answer, “From the chocolate chip factory,” but decided to take advantage of a teachable moment and said, “Well, chocolate is made from seeds of the cacao tree that grows in the South American rainforest.”

If you know any six-year-olds, one question inevitably leads to another. So began a conversation about rainforest plants, animals and people that tested the limits of my understanding — all for the love of cookies.


Chocolate, cinnamon and vanilla beans, all from the Amazon.

As we enjoyed our cookies, we talked about other things in our house that came from rainforests. A quick online search later and we were off counting different foods, checking out the furniture and even kicking the tires on the car. As it turns out, a lot of things in our home originate in a rainforest. We easily found 30 items!


Example of mola on a quilt.

 Indigenous peoples sustainably use rainforest resources. Besides food, clothing, tools and homes, some cultures harvest rainforest animals and plants for ceremonial clothing that is passed from one generation to the next. Many cultures trade in non-food items like handmade baskets and bowls, and art produced by some cultures has found its way into our lives. The ornately patterned molas made by the Kuna Indian women of Panama can be found on purses, wall hangings or even quilts.


Example of another mola.

As a consumer, supporting companies and artisans that sustainably harvest these products can make a difference a world away. To raise awareness and enrich your child’s education, why not have your own Rainforest Celebration Day? Get your kids involved and try a rainforest product scavenger hunt or have a rainforest food-tasting party. Feeling crafty? Try making a mola out of fabric you have at home, or if like me you’d probably appliqué yourself to it, try making it out of construction paper instead! Brightly colored craft feathers (chicken, peacock, and pheasant) can be used to make necklaces, arm bands or if you’re really excited, headdresses or crowns for the little princesses in your life. 


Macaw feather headdress.

For more information on indigenous peoples, check out our John P. McGovern Hall of the Americas or the upcoming exhibit Out of the Amazon: Material Culture, Myth and Reality in Amazonia. The Cockrell Butterfly Center offers a taste of the rainforest, literally! Check out the vending machine downstairs, complete with edible bugs. Ask about our Wildlife on Wheels Rainforest topic to bring to your child’s school.

Experience a rainforest close to home with these ideas and your imagination. Happy hunting, and may all your scavenger hunts include cookies!

Educator How-to: Tectonic Chocolate Bars

The earth is vast and its surface seems huge. However, the earth’s crust only makes up 1% of the earth’s mass — subsequent layers (the mantle and the core) make up the other 99%.

So, why do we care about the earth’s crust (besides the fact that we live there)? It consists of tectonic plates that move around, and where they hit, we get nature’s most impressive formations — Earthquakes and Volcanoes. Because the crust is so vast, it is hard to see the minor changes that occur daily. We tend to notice the big changes like mountains and effects from earthquakes.

In Houston, we don’t get to see either of those things! Luckily, the Houston Museum of Natural Science has Nature Unleashed: Inside Natural Disasters on exhibit right now. In Nature Unleashed you can see how the earth’s tectonic plates shift and learn about the earthquakes that can result, build your own volcano and watch as it explodes molten rock along the mountain side. You can even experience the inside of a tornado, and see some of the aftermath found in several cities.

Nature Unleashed: Inside natural DisastersIf you can’t make it to the museum, you can always show the effects of tension, compression and shifting on the earth’s crust using a simple chocolate bar!


  • Snack-sized chocolate bars (Milky Way and Snickers work best because of the caramel)
  • Wax paper or plates to place candy on while working


  1. Tell the students that the earth’s surface is constantly changing. The crust is formed by tectonic plates which float on the plastic layer of the mantle called the asthenosphere. Where these plates interact, we notice changes on the earth’s crust. The chocolate on this candy bar is going to mimic some of those changes. This time I used Milky Way.

Structure of the Earth

  1. Have the students use their fingernail to make some cracks in the “crust” near the center of the candy bar. Ask them what they notice about the cracks in the crust?

Science Education

  1. Next, demonstrate tension by pulling the candy bar apart slowly. Notice how the crust shifts on top of the caramel layer. The caramel is the exposed upper mantle also known as the asthenosphere. It is this layer that allows the tectonic plates to move around. Sometimes this tension between plates can form basins or underwater ocean trenches.

Science Education

  1. The students should then place their chocolate bar back together gently. To demonstrate another way the earth’s crust moves, ask the students to move one half of the candy bar forward and pull the other half backwards. This is an example of a strike-slip fault. Notice how the chocolate changes at the fault line. This mimics the bending, twisting and pulling of the rocks that can occur at a fault.

Science Education

  1. Lastly, ask the students to push the two ends of the candy bar together. Notice how some of the chocolate pushes up and some even slides on top of another piece, showing how mountains can be created on the earth’s crust.

Science Education

  1. Now that you’ve seen what the earth’s crust can do, feel free to allow your students to eat their new landform creations! 

And don’t forget to come check out Nature Unleashed: Inside Natural Disasters showing now through September 14!

The sweetest story: Learn about the chocolate revolution at an HMNS Distinguished Lecture

On cold nights, one of the best comforts out there is hot chocolate. You come home from a long day’s work, take off your coat, defrost a bit (OK, we’re in Houston, so just go with me here), boil up some water, add in the mix and mmmm … hot chocolate.

Oh, the convenience of it all! But have you ever wondered what the real story of this drink was?


As modern Americans, we might consider hot chocolate to be a unique invention, seeing that much more of the chocolate around us exists in its hard candy form. But really, this drink harkens back all the way to early Mesoamerican cultures.

Cacao cultivation started as early as 1400 B.C. by the Olmec civilization. From residue left on pottery, we can tell that the Olmecs used the bean to create a fermented drink, most likely used in religious ceremonies. The Maya borrowed the Olmec’s cultivation techniques but created a drink far more recognizable to today’s chocolate connoisseurs, creating the first “modern” chocolate 2,000 years ago. The drink was associated with fertility and was also used in a ritual setting.
The Aztecs, in turn, borrowed from the Maya and seasoned it with vanilla, chili pepper and achiote to create a bitter, frothy drink called xocolatl. By this time, the beverage had become a luxury item for wealthy Mayans. Europeans would pick up on this when they came to the New World, and maintained chocolate as a luxury item for European courts until the Industrial Revolution would make chocolate accessible to the masses.

In 1828, the cocoa press was invented by Dutch chocolatier Coenraad J. van Houten. The press created a fine powder from roasted cacao beans, which dramatically lowered the production price. This, in turn, paved the way for British chocolatier J.S. Fry to make the world’s first chocolate bar in 1830. In 1875, the Swiss were the first to add powdered milk to the mix, creating milk chocolate.

Today chocolate is a worldwide industry, with 45 percent of chocolate revenue coming from Europe and two-thirds of cocoa produced in Western Africa. So to all the chocoholics out there, be grateful for the rich history of chocolate, which has made it so readily available to us today!

Can’t get enough chocolate history? Come to HMNS on Tues., Feb. 4 for “Chocolate, A Revolution in a Cup” as part of our Distinguished Lecture series. The lecture starts at 6:30 p.m., but come early for a chocolate frothing demonstration … and stick around after to taste unique chocolates from Araya Artisan Chocolate!

HMNS Distinguished Lecture
“Chocolate, A Revolution in a Cup”
Rosemary Joyce, Ph.D.
Tues., Feb. 04, 2014
6:30 p.m.

This lecture is cosponsored by Archaeology Institute of America Houston Society. Get tickets!

Teachers, get credit for hearing the chocolate doctor at a special Teacher Tuesday just for you:

ExxonMobil Teacher Tuesday
“Domestication of Plants: Chocolate”
Tues., Feb, 4, 5
8 p.m.

Examine the natural science and yummy cultural history of chocolate with hands-on classroom activities. Then attend lecture by Dr. Rosemary Joyce, who will tell how the cacao plant was domesticated to produce chocolate. Purchase tickets.