Experiment of the Week - #174 Bad Chocolate?
This experiment has to do with
discoloration that you sometimes find on old chocolate.
You will need:
* a plastic
food storage bag
* chocolate -
I used chocolate
chips and bar chocolate, using milk
Please read the safety warning
before you start. First,
eat some of the chocolate.
Notice the taste and the texture. Since we are going to change the
chocolate, we need a control to compare the results with. Keep
plenty of chocolate handy, as I found it necessary to refresh my memory
frequently. I ate almost an entire bag of semi-sweet chocolate chips
just to be sure I was familiar with their flavour.
Next, we are going to cause the
chocolate to "bloom". That is the term that is used in the chocolate
industry to describe the changes that happen in old chocolate. To do
this, put some chocolate into the plastic bag. We want to heat the
chocolate enough to partially melt it, without turning it into a puddle.
I placed the bag on the dashboard of my truck and left it there for
about 5 minutes. This worked much better than using the microwave, which
tended to melt them too quickly. The chocolate should be soft, but
should still be in a lump, not a runny liquid. If the chocolate melts
completely, then get some fresh chocolate and try again.
Once you have some partially
melted chocolate, place the bag someplace where no one will eat it. By the
following day, you should notice quite a change. The surface of the
chocolate probably is lighter colour and has very light coloured blotches.
Break off a piece and taste it. Don't worry, the light splotches are
not mold. While the taste has not changed much, you will notice a
big difference in the texture. Instead of being smooth, the chocolate
now feels grainy. Be sure to eat some more fresh chocolate to compare
What has happened? The light
coloured patches are cocoa butter, one of the main ingredients in
chocolate. When cool enough to be solid, cocoa butter forms crystals. It is
polymorphic, which means that at different temperatures, it forms different
kinds of crystals. For chocolate to be smooth and creamy, the crystals
must be very small. When we melted the chocolate and let it cool again,
it formed larger crystals, giving it a grainy texture.
Cocoa butter is monotropic, which
means that even if it does not melt, over time the small crystals will
slowly change to the larger form. To prevent this, chocolate should be
kept in a cool, dry place, but not in the freezer. If frozen,
condensation can leach out the sugar, again causing white blotches. I feel
that by far the best strategy for chocolate is to eat it all
quickly, before it has a chance to go bad.