How many Ph.D.’s does it take to make Chocolate?

If you ever want to see students and professors alike act like children, take them to a chocolate factory. When we went to the Chocolate Museum last week, I could not contain myself. I started jumping up and down for a solid ten minutes and could not hide away my huge smile. I ate bits and pieces of chocolate that fell into our table until my stomach hurt. And I made everyone laugh when I spilled chocolate on myself.

Ecstatic in my chocolate fantasy.

We got a demo on how to prepare milk chocolate. Milk chocolate requires a colder temperature than dark chocolate (closer to room temperature). So we had to pour the chocolate unto the table and move it around with two spatulas. The Chocolate Museum speaker’s quick moves reminded me of an artist painting fast yet ever precise brushstrokes.


chocolate demo


I remembered reading an earlier year’s blog post on chocolate (Bouguyon, 2015) before coming to Paris, so as I saw the demo, I knew that moving chocolate around was harder than it seemed. Hence why I was not surprised when some of my classmates struggled to move the chocolate around fast enough. I was quite surprised (and quite amused), however, at how much Dr. Frenzel and Rachel struggled at. I thought that all that pipetting and fine movements done in experiments were going to help, but it seemed like two Ph.D.’s could not keep up with the chocolate maker!

Chaos happens when you take these two out of the classroom.

The presenter’s directions caught my eye, as he said “scrape the smaller spatula on the bigger one.” So what separated his movements from the rest of ours? I hypothesized it had something to do with not only his years of experience, but also at how he looked at the task itself. He differentiated his hand movements on the basis of the size of the tool each hand held….

And that is how I ran into a study titled “Object Properties and Cognitive Load in the Formation of Associative Memory during Precision Lifting” that looks at how the size of an object and our memory of its previous use influences how we lift it up (Li et al., 2009).

In this study, researchers studied how we associate how an object looks (its size or color) to how much it weighs. Associative memory is “the ability to learn and remember the relationship between two unrelated items” (Suzuki, 2015). So we form associative memories when we learn to associate a small spoon as relatively lightweight, for example.

Researchers assigned 40 volunteers to one of four groups: color cue single task (CCS), color cue dual task (CCD), no cue (NC), or size cue (SC). Cue here implies that after a few trials, you will learn to associate an object’s feature (color, size, or neither) with its weight. In the color cue dual task, apart from associating the color of an object with its weight, participants also performed a memory task between lifting objects.

Participants had to lift three objects that weighed either 580 or 280 grams and were either green or blue colored. Two objects had the same size but different weights (580 or 280 grams), while two of the same objects had a different size but same color.

Objects had to be lifted with three fingers (thumb, index, and middle finger), since that way objects are all grasped at around the same angle (2.3 Task). There was a sensor inside each object that measured the force (horizontal and vertical, in Newtons) and acceleration (m/s) at which each object was picked up (2.2 Apparatus).

Figure 1 (Li et al., 2009). Diagram of the objects and force measurement device used.


Participants heard a tone to indicate they had to lift the object as fast as they could. Four seconds later, they had to put the object back down. Each participant completed 2 trials (color, size, or no cue lifts) of 18 times each (36 total).

To study how much force the participants estimated they needed to lift each object, researchers calculated how much force was exerted during the first 70 ms of an objected being lifted. Since it is so early in the process of lifting an object, this short timespan tells researchers more about how much force participants though they needed. For example, has it ever happened to you that you imagine an object is heavier than it actually is? So at first you do an awkward movement where you exert more force than you actually need to (take that to be the first 70ms researchers are analyzing). Quite quickly though, you realize that the object isn’t as heavy as you first thought and exert less force than you did during those first milliseconds (hence why researchers did not look at how much force participants exerted overall or later on during those 4s).

Figure 5 (Li et al., 2009). Y-axis (label not provided) measures average grip force (N).

Researchers found that participants relied the most on size to estimate how much force to use when lifting an object with unknown weight (Fig. 5). Put another way, they showed the most difference in how much force they used when picking up objects of different sizes. Results also showed that participants learned to associate, to a lesser extent, an object’s color with its weight (Figure 5).

So this study suggests that our lovely Ph.D.’s can someday also succeed at mixing chocolate just as well as the museum speaker could. All they might need could be some more practice, so they too can learn to associate how much force they should use when using the small and big spatula.

And just to make you jealous, I will let you know that I am writing this while having the best hot chocolate in all of Paris at Café de Flore. If you come to Paris, do not leave without trying it!

Truly a must-have in Paris!



Bouguyon, K. (2015). Making Chocolate like a Pro | NBB in Paris. Retrieved June 26, 2017, from

Li, Y., Randerath, J., Bauer, H., Marquardt, C., Goldenberg, G., & Hermsd?rfer, J. (2009). Object properties and cognitive load in the formation of associative memory during precision lifting. Behavioural Brain Research, 196(1), 123–130.

Suzuki, W. (2015). Associative Learning and the Hippocampus. Retrieved June 26, 2017, from

Pictures taken by writer, with consent of persons depicted. June 2017.

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