What's really happening in a conch vs. a melanger?

May 9 2019

My current research tests the melanging stage of small-batch chocolate-making. Most people haven’t heard of melanging, because when you take a tour of the Hershey’s factory, or look up “How to make chocolate” on the Cadbury’s website, it’s not mentioned there. This is a step that only takes place with very small-batch, bean-to-bar chocolate makers. For now, I’ll assume my limited audience knows or can guess what those words mean. Instead of hearing “melanging”, you are more likely to hear of a related process called “conching". Although the two are quite different, it’s worth examining conching as a means to shed some light on melanging, which is a relatively little-known process. In fact, only one paper has been published on the subject so far. Conching, on the other hand, is well-understood, because it is a large-scale industrial process that has been in use for hundreds of years (Stephen T. Beckett, 2006; Gasparotto, 2018; Hartel, von Elbe, & Hofberger, 2018).

Most people who know anything about chocolate are already familiar with the concept of conching, but they may not really understand what is happening on the on the chemical level during this stage. Let’s examine it in more detail.

Conching is really the last step of industrial-scale chocolate-making. Before chocolate enters the conch, it has already been fermented, dried, roasted, cracked, winnowed, pressed, and refined (more on all these steps in later posts). The refining step, just before conching, takes place in large horizontal rollers that press the powdered chocolate paste at high pressure, reducing its particle size to below 25 microns. At this point, the human tongue can no longer distinguish one particle from another. The range of 20-25 microns is considered the ideal diameter range for the particles in chocolate for this reason (S. T. Beckett, 2009; Stephen T. Beckett, 2006; Tan, n.d.). What this means is that, contrary to popular belief, conching is not a “grinding” step. In fact, chocolate-makers want to avoid that particle size reduction continues to take place in the conch, because if particles grow smaller and smaller, chocolate can become gummy and thick to the point of seizing. This effect becomes noticeable below 10 microns (Tan, n.d.), and certainly below 4 microns it has been documented (Stephen T. Beckett, 2006).

The reason for this shift is that cocoa butter fats evenly coat all particles during the conching phase. If there are a high number of very small particles in the mass, too much cocoa butter fats are “used up” coating these tiny particles, and not enough fats remain to evenly disperse all particles. This fat coating is certainly one of the main objectives of the conching step. If conching is performed correctly, all particles—which should all be within 20-25 microns in diameter—will come out of the conch evenly coated in a thick layer of cocoa butter acting as the continuous phase.

In order for all particles to receive their coating, “chunks” of particles known as “agglomerates” must be broken up. This is another goal of conching (Ziegler, 1999). The agglomerates often form during the refining step that precedes conching, when moisture level has not been sufficiently reduced (Fryer & Pinschower, 2000). The agglomerates must be broken up entirely so that each individual particle can be coated with cocoa butter.

Moisture is also being lost in the conching phase. Dark chocolate might already be as low as 0.75% or 1% moisture when it goes into the conch, although milk chocolate’s moisture level is higher, but even more moisture must be lost because chocolate is extremely hygroscopic and will thicken undesirably with even a small amount of moisture (Fryer & Pinschower, 2000). Conching is performed with heat, either through friction or by the application of heat energy, and this heat gently evaporates water, reducing the moisture level (Fryer & Pinschower, 2000; Hartel et al., 2018). For this reason, all conches are vented in one manner or another (Stephen T. Beckett, 2006).

Along with moisture, any steam-volatile flavor compounds can also escape through the vent (Fryer & Pinschower, 2000). The most important of these are volatile organic acids—usually acetic acid, which is generally considered undesirable, although I don’t personally think that is the whole story. So far, my research is showing an interesting story with acetic acid, but I’ll have to talk more about that after I examine the data more.

A lot of flavor development is happening in the conching step, generally. In the early stages when more moisture is present, water-catalyzed reactions take place. In later stages, moisture is lacking, but heat is still important for flavor and aroma reactions. It is impossible to say what, exactly, is happening on the chemical level, because the precise reactions are dependent on tiny differences in temperature, starting materials, moisture level, etc. Owusu, Petersen, and Heimdal (2012) have studied flavor and aroma development in conching, and so have Albak and Tekin (2016) and Ducki et al. (2008). Glicerina et al., (2014) and Afoakwa, Paterson, and Fowler (2007) and looked at its effect on texture and rheological properties, and still others have examined how conching affects other attributes like bioactivity and appearance.

So how does knowing all this inform us about the melanging step? Well, melanging is very similar to conching in that it uses both vertical and horizontal shear forces to homogenize and aerate the chocolate mass, breaking up agglomerated particles and evenly coating all fragments in cocoa butter. It is accompanied by heat—from friction, in the case of melanging—and is ventilated to allow moisture and volatile compounds to escape. However, melanging is not only a texture- and flavor-development step; it is also a refining step, meaning that grinding takes place in the melanger, rather than beforehand (as in conching). So all the processes described above are taking place in a melanger, but the particle size is being reduced simultaneously.

Because of this, melanging tends to take place for a much greater length of time than conching—at least modern conching (although chocolate-makers have always been secretive about their processes, it is rumored that early conching processes took nearly as long as a melanging step takes today) (Bordin Schumacher et al., 2009; Gasparotto, 2018).

I will discuss melanging in more detail in a later post, but I hope for now I have at least given some information about what conching is, what it is for, and how it is different from melanging.

Works Cited

Afoakwa, E. O., Paterson, A., & Fowler, M. (2007). Factors influencing rheological and textural qualities in chocolate - a review. Trends in Food Science and Technology, 18(6), 290–298. https://doi.org/10.1016/j.tifs.2007.02.002

Albak, F., & Tekin, A. R. (2016). Variation of total aroma and polyphenol content of dark chocolate during three phase of conching. Journal of Food Science and Technology, 53(1), 848–855. https://doi.org/10.1007/s13197-015-2036-4

Beckett, S. T. (2009). Conching. In Industrial Chocolate Manufacture and Use: Fourth Edition. https://doi.org/10.1002/9781444301588.ch9

Beckett, Stephen T. (2006). Using Science to Make the Best Chocolate. Retrieved May 8, 2019, from https://www.newfoodmagazine.com/article/1949/using-science-to-make-the-best-chocolate/

Bordin Schumacher, A., Brandelli, A., Schumacher, E. W., Carrion MacEdo, F., Pieta, L., Venzke Klug, T., & Vogt De Jong, E. (2009). Development and evaluation of a laboratory scale conch for chocolate production. International Journal of Food Science and Technology, 44(3), 616–622. https://doi.org/10.1111/j.1365-2621.2008.01877.x

Ducki, S., Miralles-Garcia, J., Zumbé, A., Tornero, A., & Storey, D. M. (2008). Evaluation of solid-phase micro-extraction coupled to gas chromatography-mass spectrometry for the headspace analysis of volatile compounds in cocoa products. Talanta, 74(5), 1166–1174. https://doi.org/10.1016/j.talanta.2007.08.034

Fryer, P., & Pinschower, K. (2000). Materials science of chocolate. MRS Bulletin, 25(12), 25–29. https://doi.org/10.1557/mrs2000.250

Gasparotto, T. (2018). Le Chocolat dans touts ses etats.

Glicerina, V., Balestra, F., Rosa, M. D., Bergenhstål, B., Tornberg, E., & Romani, S. (2014). The Influence of Different Processing Stages on Particle Size, Microstructure, and Appearance of Dark Chocolate. Journal of Food Science, 79(7), E1359–E1365. https://doi.org/10.1111/1750-3841.12508

Hartel, R. W., von Elbe, J. H., & Hofberger, R. (2018). Confectionery Science and Technology. https://doi.org/10.1007/978-3-319-61742-8

Owusu, M., Petersen, M. A., & Heimdal, H. (2012). Effect of fermentation method, roasting and conching conditions on the aroma volatiles of dark chocolate. Journal of Food Processing and Preservation, 36(5), 446–456. https://doi.org/10.1111/j.1745-4549.2011.00602.x

Tan, J. (n.d.). Development of Fast and Affordable Methods for Measuring Quality-Related Properties of Confections. https://doi.org/10.1021/ic9611812

Ziegler, G. (1999). Research spurs new conching processes. Candy Industry, 164(6), 50–54. Retrieved from https://dialog.proquest.com/professional/docview/836228142?accountid=131175%0Ahttps://www.rightfind.com/vlib/order/OpenURLReceive.aspx?issn=07451032&date=1999-01-01&volume=164&issue=6&pages=&title=Candy+Industry&atitle=Research+spurs+new+conching+processe