The saddest cake story

CakeDNARemember when I made a DNA cake that spelled “CAKE”? Shortly after that did the rounds on the internet, people spotted mistakes. The helix was turned in the wrong direction, and I had failed to stay on the same strand in the twist so the colours were wrong in every other segment.

Did it make the cake less fun or delicious? Not really, but I still felt dumb for introducing those errors. I really should know better. I have a PhD in baking — I mean, biochemistry.

So, when I recently had an opportunity to bake a cake for scientists again, I thought this would be a good moment to redo it, and fix the errors.

At work we drew names of the contestants of Great British Bake Off, and the week after “your” contestant left, you’d bring in something you baked. The name I had drawn was Rav, who was known for liking vegan baking, so I thought that’d be a great excuse to also use my favourite vegan cake recipe.

When Rav left the show a few weeks ago, it was my turn to bake, so I set aside several hours of my weekend to prepare everything. I finished the final icing details on Sunday morning, and, as planned, made a correct DNA helix this time. The twelve base pairs encode the four amino acids with the one letter codes “C-A-K-E”, the helix turns the correct way, and I followed the strands in the twists. Everything was perfect!



Except, a few hours after I finished, I wasn’t feeling very well. I started getting a stomach ache that only got worse and worse. At midnight I ended up going to the hospital to find out what was wrong, and around 2AM I was told I had gastroenteritis. I had to stay home from work until I was all better, and, worst of all, I was not allowed to prepare food for other people!

My beautiful cake! Not only could I not go to work myself, but I wouldn’t be allowed to serve the cake to ANYONE! I had to throw it out.

I actually left it in the fridge for a full week until I could bear to part with it (and until I could deal with the concept of “food” and “cake” in general.)

Goodbye, beautiful DNA cake.

This cake contains theobromine

A few weeks ago it was my turn again to bring cake to work. Two years ago I made a DNA cake, last year I made a dinosaur cake, and this year I made theobromine cake!

Theobromine is found in chocolate, and is chemically related to caffeine. The difference is just one methyl group.

Obviously, the cake had to be a chocolate cake. I used this recipe for vegan chocolate cake, but I used a (non-vegan) icing to hold the different parts together.

For the theobromine molecule, I braved the M&M store on Leicester Square, where you can pick and mix the exact M&M colours you need. In my case: black for carbon atoms, white for hydrogen atoms, red for oxygen atoms, and blue for nitrogen atoms.

I originally planned to make this cake for the Comic Relief bake sale, so I also bought a LOT of red M&Ms in addition to the ones I needed for the molecular structure. My actual baking day ended up a few weeks later, but I still wanted to use my massive bag of red M&Ms, so I made a piñata cake. The idea is that when you cut open the cake, M&Ms roll out.

The cake was a bit less bouncy than would have been ideal for a pinata cake, and the icing held many of the M&Ms inside, but the effect was still somewhat in place. See the video for the entire cake making and cake slicing process.

How to make a dino cake

CakeDNA1. Realise that your turn to bring cake to work is coming around, and everyone still remembers that DNA cake you made last year.

2. Try to think of another science-themed cake, and remember the dinosaur cookie cutters you won by dressing as a TARDIS at Science Online.

3.  Look up dinosaur cakes online. Oh wow, those are all really impressive.

4. A few weeks before your cake is due, try a test cake, inspired by this cake with fossils inside.

5. Fail miserably.

6. Eat cake for breakfast a few days, until you really can’t stand leftover cake anymore and throw the test cake out.

7. Decide to just keep it simple for the actual cake: two layers of sponge, frosting in between, layered in ready-to-roll icing.

8. Buy all the necessary ingredients. Again, keep it simple: Buy pre-mixed chocolate cake mix for the sponges. It’s meant for cupcakes, but it will be fine.

9. Make a schedule to figure out when various biscuits and cakes need baking or icing. To be ready by Friday, the first baking round is on Tuesday morning.

10. Get up early on Tuesday to bake the first round of dino biscuits.

2014-06-03 20.52.4911. Ice the dino biscuits Tuesday evening and bake a few more. This is going so well!

12. Get up early again on Wednesday, this time to bake the layers of the cake. This instant cake mix is so easy: just add eggs and water, mix, and bake. What could possible go wrong?

13. Bake a few cupcakes with some left-over cake mix (in another colour) from the previous week’s failed cake experiment.

14. Take the cake layers out of the oven, and watch one of them instantly, spectacularly, collapse.

2014-06-04 08.41.59

15. Panic.

16. Despair.

17. Message cake expert Jonathan for help, even though it’s before 9AM and he’s busy with FameLab at the Cheltenham Science Festival.

18. Go to work, and come home to find the second cake half has also slowly collapsed during the day.

19. Make a large amount of frosting, using some instant coffee you took home from a hotel that one time.

2014-06-04 19.21.0720. Fill the cake craters with bits of cupcake and lots of frosting.

21. There isn’t enough frosting. Make more, using  coffee from another hotel.

22. Add the other cake half and assemble the cakey mess into something vaguely cake-shaped.


2014-06-04 19.53.46

23. Roll out icing and cover the cake-shaped thing with it until it looks like a real cake.

2014-06-04 19.53.54

2014-06-04 21.51.46

24. Since you used up all the icing sugar in making the frosting to fix your mistakes, buy some more at lunch time the next day.

25. That evening, spend about an hour practicing how to draw a very basic T. rex skeleton, and copy it onto the cake in icing sugar.

2014-06-05 19.07.51

26. On Friday, serve biscuits and cake at work, and realise that basic drawing skills trump mediocre baking skills.

2014-06-06 15.28.16

27. Vouch to just bring a cabbage covered in icing sugar next year.


It was my turn to bring cake for cake club at work. Your turn only comes around once a year or so, so I thought I’d make something interesting. Inspired by Jonathan’s DNA cake, and by the four colours in use for the four products at our company, I designed a cake with a repeating DNA sequence, that, when translated, becomes a short peptide with the amino acids Cysteine – Alanine – Lysine – Glutamic Acid. Or, in their one-letter codes, C-A-K-E.

There are multiple possible DNA sequences that all spell out C-A-K-E, because the code is degenerate, but I went with this one:


I picked a colour for each base, and started drawing coloured bars underneath the corresponding letters.

Then I figured out how many helix turns would fit on the cake, and how many base pairs would fit in a turn, and when it was time to ice the cake, I recreated my sketch in icing.


Eagle-eyed geneticists will have spotted that I made a mistake, but I didn’t notice this until it was pointed out to me on Twitter after it had already been tweeted and retweeted to at least ten thousand people!

Screen shot 2013-06-09 at 11.42.46

Argh! *headdesk*

I can’t believe I forgot to consider the turns… After I figured out how many base pairs fit in a turn, I should have alternated every other turn so that the sequence stayed on the same strand.

So my cake didn’t pass rigorous scientific peer review, but it tasted good anyway.

Bread Science

breadbook1.jpegBread Science: the Chemistry and Craft of Making Bread is a book with practical tips on baking, but it also explores the science behind bread. The author, Emily Buehler, has a PhD in chemistry from UNC Chapel Hill. After graduating, she started baking bread at Weaver Street Market in Carrboro. (I shopped there the day after the Science Blogging conference. It’s a small world…)

“In 2002, at the request of community members, Emily and a fellow baker began teaching Beginning Artisan Bread-Making classes through Weaver Street Market and the Carrboro Artscenter. (…)
Emily’s search for the details of bread-making science began when she wrote the manual for her class. Unable to find a good source, she pulled bits and pieces together from various places–biology textbooks, notes in recipe books, high-tech books on commercial baking, newsletters of the Bread Baker’s Guild of America, and a few scientific journal articles. A more thorough search confirmed her belief that a comprehensive, understandable bread science book was needed.”

The book is for sale online, or in some specialized independent bookstores in North Carolina, Knoxville (Tennessee), New York City, and Toronto. Large excerpts from the book are also available on the site.

The book explains about starch, sugar, fermentation, and other biochemical concepts involved in baking bread.

Why is bread not glue?

by simpologist on FlickrAfter a pinata party, Maria e-mailed me the following question:

Hey, why does water with flour become glue for pinatas? Is there a scientific explanation for the stickiness? How come it doesn’t work like that when it makes bread? Is bread sticky too? I’m really confused!

Off the bat, I knew that flour has starch and the starch makes the glue sticky, but then I started wondering too. Why is starch sticky? And why isn’t bread dough more like glue?

Starch is the major component of flour. Starch exists in tiny granules, which swell and break when boiled in water. This releases the starch molecules, which then all stick together to make a goopy, gluey mess. [1]

Starch glue
You can make starch glue from flour and water, by mixing one cup of flour in some cold water, and adding this mixture to 3 cups of boiling water. You can even use less flour, and it will still work. [2]
Starch glue is good at sticking paper to paper, to make pinatas for example, because paper itself contains cellulose, which is quite similar in structure to starch. They’re both polysaccharides. You can’t use starch glue to glue plastic or metals – only other polysaccharides. [1, 3] (In making pinatas, the first layer of paper sticks to the balloon. I think this works because while the glue is still wet the wet paper will stick to the balloon. Once the glue is dry, it actually doesn’t stick to the balloon anymore, but at that point the paper has been permanently shaped around it.)

Like starch glue, bread dough also contains water and flour. Still, it’s not as sticky – you can’t use bread dough to glue paper together. Let’s look at the ingredients for a super simple bread recipe to find out what’s different.

Ingredients for bread
1 c. milk (Hot)
1/4 c. sugar
4 T. margarine
1 tsp. salt
1 pkg. yeast
1 egg
4 c. all-purpose flour
1/4 c. warm water

Instead of 1 cup (or less) of flour and 3 cups of water, we now have 4 cups of flour and 1.25 cups of warm water and milk. (The rest of the ingredients don’t add a lot of water or starch, so I ignored them, although they will make a difference to the final dough: the yeast, for example, makes the dough rise.)

The ratio between the flour and water is completely different between glue and dough. Would this be crucial in whether or not it’s glue?
According to this website on the science of bread ingredients, the amount of water is indeed the answer:

In bread making not as much water is added as when making a sauce or gravy, and gelatinisation isn’t completed – the starch granules swell, and many don’t burst to form a gel. This forms a network of bloated starch granules all touching at the edges. [5]

So there you go: water and flour glue is sticky only for paper and other cellulose-based materials. It’s the large amount of water that makes it sticky, because it releases the starch from starch granules. Bread dough doesn’t have that much water, and therefore isn’t as sticky.

Pi Day

March 14 is “Pi Day”, according to fans of the number, because the date can also be written as the number pi rounded down to two decimals: 3.14
The Exploratorium in San Francisco has been celebrating Pi Day since 1988, and kicks off at 1.59 PM (3.14159…) by “(circumambulating) the pi shrine 3.14 times while singing happy birthday to Albert Einstein”. That’s right, it’s also Albert Einstein’s 127th birthday today.
The mathforum website offers tips for teachers to celebrate pi day in the classroom. Most of them involve maths, obviously, but there are also suggestions to teach about the history of pi.
Another favourite activity is to celebrate pi day by eating pie! While a round pie appears to be very appropriate (after all, the circumference of a round pie is “pie” times the diameter) some people actually prefer a square pie on pi day. Why square? Well, isn’t it obvious: the equation for the surface area of a circle clearly says Pi*r2, or “Pie are square”!

Science of Cooking

The Science of Cooking on the Exploratorium website is all about the science behind the things you eat. It not only gives good “daily life” examples for general concepts of chemistry, such as as the Maillard Reaction, but is also informative for people who love cooking and just want to know how it works. What happens when you bake bread, for example?
The site tabs lead to five different types of food to learn about: meat, eggs, bread, pickles, seasoning, and candy. Pickles get their own category because they’re all about salt and food conservation, and candy gets its own because it’s the most important food group! (And because it explains the science of sugar.)