Could you compress chocolate such that it has the same density and shape as a real copper coin?

Question

There are many cultures around the world that have traditions of chocolate coins around Christmas time, mine included. Recently I wondered if it was possible to compress chocolate to give it the same density as a real coin (which are mostly made of copper I believe, though the exact composition is not that important). There is no real purpose to this question, other than entertaining the idea that you could trick people into thinking these are actual currency instead of the chocolate kind.

Assuming a coin is made of 100% copper, it would have a density of about 8960 kg/m$^3$, whereas chocolate has a density of about 1300 kg/m$^3$. This means you would have to compress it to about 1/7th of its original volume. Since chocolate has a non-zero compressibility, I figure it is possible to get it to that density, but would the chocolate still retain similar physical characteristics during the process, or would the pressure needed cause other effects that make this impossible? I have little experience in the subject of material science, so I wasn't able to get to good information regarding chocolate under pressure, mostly about effects of chocolate on blood pressure.

Any chance someone has a hydraulic press to do a taste test afterwards?

Edit: Source for the density of chocolate https://www.density.co.uk/documents/Density-of-Chocolate.pdf

Answer 1

The heroes we deserve are Bikos, D. et al., "Destructive and non-destructive mechanical characterisation of chocolate with different levels of porosity under various modes of deformation," 2023. They managed to achieve a permanent (inelastic) compression of about 3%. No word on how that affected the taste or mouthfeel.

For the behavior of chocolate under more extreme compression, further research is clearly needed. However, it might be interesting to look at the interior of the sun as a comparison. The sun is made of hydrogen. Liquid hydrogen reaches a density of about 70 kg/m$^3$ at 1 atmosphere, but obviously becomes denser under high pressures. To get the density 7 times higher, you have to go (very roughly) 40% of the way towards the center of the sun, at which point the pressure is about 20 TPa. [1] (For comparison, the pressure at the center of the earth is only 360 GPa.) Unfortunately, the high temperatures inside the sun are a confounding factor, and chocolate is not the same as hydrogen [citation needed], but this should give you an idea of the extreme conditions required to achieve that kind of compression.

The bottom line is that a hydraulic press is not going to do the trick. If you want to compress chocolate to a density of 9, you are going to need to hire the engineers who design the explosive lenses used in nuclear weapons, and even that might not be enough.

[1] data from https://www.sns.ias.edu/~jnb/SNdata/Export/BP2004/bp2004stdmodel.dat

Answer 2

It is definitely theoretically possible -- given high enough pressures anything can be compressed to that density. However, there are multiple problems which would prevent you from tasting the product:

1. Bulk modulus of chocolate will be in gigapascals, and compressing it by a factor of seven would thus require pressures on the order of $10^{12}\ \mathrm{Pa}$. Such pressures are way too high to be achieved with non-destructive methods. It would require high (or maybe even nuclear) explosives.
2. Even if it were possible to design a sufficiently powerful press, you would not be able to taste it in the compressed state. When the pressure is removed, chocolate would expand back (nearly) to its original volume.
3. It is quite likely that irreversible chemical changes would happen, since the compression with explosives is necessarily very fast. I suppose that the final state of the matter would be a mix of carbohydrates that would resemble crude oil rather than chocolate.

Answer 3

Chocolate has traces of naturally occurring heavy metals such as cadmium. But Cadmium has a lower density than copper, unfortunately (or fortunately for the eater since cadmium is toxic). Otherwise, you could accomplish your objective by sufficiently increasing the proportion of denser components of chocolate.

However, if you added denser elements such as silver or gold, you could make an edible chocolate mixture as dense as copper. It would probably be expensive and not so tasty, but silver and gold are not toxic and should not harm anyone who eats them.

Zchocolat actually makes edible chocolate encrusted in gold. It's pricey.