Chocolate molds, better ones anyway, are made with polycarbonate, which generally contains BPA or a related chemical. These chemicals have gotten a lot of press for mimicking hormones. I have seen some BPA free molds but they're still a rarity.

Does BPA enter the chocolate during molding? Is contact too brief? Temps too low? Or are we just turning a blind eye?

In short, the answer is we don’t know.

There is just no data out there so it leaves answering the question to speculation and my background in chemistry. In some places that is called ‘speculation’. Or an ‘educated guess’. Basically, I’m ‘theorizing’. But since I’m not giving concrete conclusions, it can at least be said that I am not ‘making sh!t up’ !

I am rather glad you didn’t get into asking my thoughts on whether BPA is a concern, but that is a real hot spot of contention. Regardless, there was some good data I was able to collect along the way.

BPA is the friendly abbreviation for Bisphenol A. Which is also a friendly name for it’s IUPAC name of 4,4'-(propane-2,2-diyl)diphenol. And thank goodness for standardization as its original name was either p,p'-isopropylidenebisphenol, or 2,2-bis(4-hydroxyphenyl)propane.

It has a solubility in water between 120 and 300 mg/L. It is freely soluble in oils, fats and organic solvents. Because of this later piece of data, it is theorized that the contamination to oily or fatty products (like fish in oil vs fish in water) would be higher, but I could not find one single piece of data to support that assersion….which means to me that people most likely are ‘making sh!t up’.

Part of the reason I say this is there is precious little data to support a direct link between solubility and leaching. They are two different animals as it were. Leaching in the most simplistic terms might be considered surface solubility. But only kind of. Solubility involves a solvent (let’s say water) surrounding and encapsulating the solute (the BPA). It requires the solvent to get between the molecular spaces of the solute in order for it to surround it and carry it off into solution. With leaching, it’s more a matter of what can the ‘solvent’ shake loose and carry away. Analogy time. You have dirt rubbed into your shirt. And the dirt here is powdered rock and sand but also clay and hummus. Stuff that isn’t soluble in water (the rock) and stuff that is soluble in water (the hummus). If you put that shirt in a bucket of water and don’t agitate it you will find that the water starts to color. The soluble hummus is being surrounded by water molecules and carried off. But the sand and rock stay imbedded. It takes agitation to shake them loose or ‘leach’ them from the shirt. Kind of make sense?

As for numbers to show leaching has little correlation to solubility, let’s look at that solubility of BAP vs what is found in two different ‘solvents’. Recall the solubility in water is 120-300 mg/L or ppm. That is the maximum that can go in. The levels found in water are 0.1-10 ug/L. The levels found in liquid baby formula were 0.8-11 ug/L. There are two things to notice here. The first is that the amount found is roughly 1/10000 the solubility level. Hundreds of parts per MILLION vs parts per BILLION. Next, to me, those two leaching values are basically identical. The ‘high’ fat formula had no noticeable effect on how much was leached. Now, please know, I am NOT saying oil won’t leach more…just that I can’t find any evidence of it. Which is a good thing for chocolate since it is 30-50% oil.

The next bit of good ‘evidence’ for chocolate comes from ‘modes of transmission’. We have looked at how BPA leaches into a liquid over time. But there are other ways for it to transfer. Solid to solid is another way. In the same study that liquid baby formula was looked at, they also examined powdered (high fat) baby formula in lined containers….and only found BPA in one of 14 of the samples. That’s good news. My suspicion why is because the container was rigid and the ‘solvent’ (being a solid) could not knock, brush or liberate any BPA from the surface of the lining (sort of like in a chocolate mold).

And this is kind of confirmed, or at least not contradicted by the fact that one of the highest forms of transfer was from thermal receipts that contain BPA. In this case, although both surfaces (the paper and your hand) are both solids, the contaminated surface was highly flexible so was able to ‘slough’ off BPA readily. Think again to our shirt example. It’s dirty. And so is a rigid baseball cap. If you pick up and handle both, which is going to get more dirt on your hands? Most likely the shirt. It gives, the dirt cracks, and readily falls onto and transfers to your hand. It has a reason to move because it’s being dislodged by physical means.

Temperature does play a role in leaching.  Higher temperatures (150-210 F) leach more (2-10x more) but chocolate is not molded anywhere near those temperatures.  Good for us. And one final note on leaching. It takes time. When I was in the lab we performed an extraction called a Toxic Characteristic Leaching Procedure (TCLP). In the procedure, we added what we wanted leached into a container with a leaching solution (not even called a solvent) and this was agitated (tumbled actually) for 24-30 HOURS. Which makes sense as the highest contamination is found in water bottles and canned foods where they sit for quite a while and are moved and agitated. My main point here is that time is a critical factor. In a few circumstances we did ‘instantaneous’ leaches for curious customers and found radically reduced leaching rates. Again on the order of 1/100 to 1/1000 times less.

So, here is what I see and could find in regards to BPA contamination and leaching.

  • Leaching is not directly related to solubility so oil vs water is does not matter.
  • Leaching is related to the surface of the material in question. Solid surfaces show much less contamination than highly flexible surfaces.
  • Leaching is related to time to some degree, with instantaneous leaching from solid/liquid boundaries being very low.
  • Leaching from one solid to another solid (powdered baby formula in a rigid container) is very low.
  • Leaching increases as temperature increases.

With all that in place, my gut feeling is that the contamination from polycarbonate molds to chocolate should be very low because:

  • The mold is rigid.
  • The chocolate although oil based does not increase transfer.
  • The time it is fluid is VERY low.
  • Chocolate is molded at 'cool' temperatures.
  • Solid/solid contact shows nearly no transfer potential.

Basically I can’t find any good reason that there should be hardly any transfer at all from polycarbonate molds to molded chocolate. But I want to re-iterate, I am just following a logic and data trail and we don’t know. To know for sure would take an actual analysis. Which honestly I am stunned has not happened and been published. Anyone?

So, to specifically answer your questions:

I don't know if BPA enters chocolate during molding, but evidence indicates probably very little

Yes the contact is too brief and of the 'wrong' type.

Yes the low temperature helps keep it to a minimum No, at this point now, we are not turning a blind eye...but maybe someone should test. That’s my take.