AskTCL: Conching and Viscosity

AskTCL: Conching and Viscosity

Greg, a ChocolateLife member, and craft chocolate maker, Asked TheChocolateLife two questions:

Further information

I make 70% dark chocolate without additional cocoa butter and have quite a variety of viscosities at the end of the refining process. It is not consistent with cocoa bean origin either--e.g. two batches of 70% Dom Rep Zorzal produced in the same machine could have two different viscosities from week to week.

I use three table-top DCM tilting melangers and one DCM 20 melanger. The batches run for 24 hrs without sugar and then run for an additional 16 hrs with added unrefined cane sugar for a total processing time of 38-40 hours. My gut points to the sugar or the interaction of the sugar + cocoa solids, but I could be very wrong. I've had batches that had comparatively low viscosity and were very easy to work with. I just can't seem to figure out how I did it.

Questions About Conching

What is the effect of heat during the conching/refining process? I understand heat can cause volatile compounds to quickly evaporate, but is that the only effect?
The first thing to get completely clear about is that melangeurs are not conches. Melangeurs may be able to perform most aspects of conching, but they are not particularly good at it. This is because they were not designed to conche, they were designed to reduce particle size and mix things.

Most craft chocolate makers use their melangeurs as “universals” in the sense that all of the grinding, mixing, refining, and conching are done in the same machine.

That out of the way ...

Heat can have an effect on how quickly the fat in the cocoa beans is expressed – you observe this when you add cocoa beans to the melangeur. The temperature of the nibs and the stones, in addition to how much add a a time, will affect how long it takes for the nibs to fully liquify. Furthermore, the pressure exerted by the spring on the grinding wheels introduces another variable to consider.

As a general rule, you want to get the mass of nibs being refined to above 60C as quickly as possible because acetic acid evaporates much more efficiently above this temperature while there is still even small traces of water remaining in the nib. Once the acetic acid aroma dissipates, lower the temperature.

This is, in fact, the reverse of the way most people use melangeurs. The first step is to refine and then “conching happens” only once the desired particle size is achieved. If you wait until the end to “conche” it takes a lot longer for volatiles you don’t want to dissipate. And remember, you won’t smell or taste some of those volatiles until the acetic acid has been completely driven off.

If you use your melangeur in the more conventional way, if you run it hot after the addition of milk powder, the heat can introduce some caramelization notes. Melangeurs normally don’t get hot enough to caramelize sugar.

Questions About Viscosity

What contributes to viscosity of chocolate outside of fat content? Is it possible that the timing of the addition of sugar and the heat of the overall batch could affect the viscosity?

After actual fat content, particle size is a factor. If the center of particle size distribution (PSD) is too low (e.g., much below 15 microns) and/or there is a very long tail of much smaller particles, the viscosity of the chocolate will be negatively affected.

If you don’t own a grind gage – even an inexpensive one you found on Amazon – you are missing an essential tool as a chocolate maker in understanding why some batches work and others don’t.

This is definitely a case where you don’t get what you don’t pay for.

And, get a grind gage, not a micrometer. The micrometer can tell you the largest particle size, but not the center of PSD nor show you the presence and quantity of small particles.

Another factor to consider is that one technical requirement is that all of the particles are completely covered in fat. If they are not, the rheology (flow characteristics) of the chocolate will change.

And just to throw in another variable – consider that the humidity levels of the nibs and the sugar may not be consistent, just as ambient humidity can change wildly depending on weather conditions.

One recommendation I make to all my consulting clients is to have a digital hygrometer installed in the workshop. Ideally there is at least a 24-hour max recording, and writing down the humidity in the production log should be standard practice. In some locations I recommend a more comprehensive digital weather station so you anticipate any potential changes in humidity.

There are also humidity measuring devices for cocoa beans. They are not cheap (nor are they expensive). Get one. Use it on beans and roasted nibs. Understand what you’re working with.

Sugar is hygroscopic, meaning it will absorb moisture in the air – and from the chocolate if there is any.

Just from experience, I would guess that the results in the three Premier grinders are generally  close-ish to each other while being different from the larger machine, when sampled at the same time in the process.. This is to be expected because of their different sizes and the different mixing efficiencies of the wheels and scrapers. Speaking with Bhavani of DCM, a key aspect of the small melangeurs effectiveness comes from the size and position of the scrapers and even small changes can completely change results.

Some Thoughts

My personal feeling is that you’re overrefining before adding the sugar – you should be able to get to the particle size you want on the liqour, or at least in the ballpark, much faster.

What really takes the time to refine is the sugar – the crystals are much harder and take much longer. However, sugar can act to hold in volatiles you don’t want, so I would personally run the melangeurs hot at the outset to get rid of the acidity quickly and then add some of the sugar to quickly lower the temperature. Make sure to weigh the sugar and time when you add it so there’s consistency there as differences in time, weight, humidity, and other factors will influence the results.

In other words, “conche” the liquor for flavor up front then refine until you are happy.

I would also blend batches of “the same” chocolate. Blending, say, six batches of your 70% Zorzal will reduce any batch-to-batch differences. There is ZERO harm or foul in this type of blending. It’s all the same chocolate, they only thing that changes is the size of the batch. (And you can to the blending while tempering.)

Finally, and I know people hate when I say this: from reading your description you’re not adding cocoa butter. My advice is always to add enough cocoa butter to make your life easy. Tempering and molding will be MUCH easier, even in very small amounts. Also, technically, chocolate liquor must have 50% by weight of fat. From my reading of the FDA regs, adding cocoa butter to reach 50% does not have to be declared on the label. But IANAL and I would have a lawyer with experience in the area take a look at the definition for chocolate liquor in CFR 21.163.

Have advice to share?

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