Chocolate Maker's Series Part III-Modern Roll Refining and Conching
Posted by Jeff Stern on August 10, 2017
Last week we discussed roller refining and conching. We are now going to get into some of the more technical details of roller refining in this post. We'll then follow up in additional posts on some of the technical details of modern conching and stone grinding.
A proper, modern production line using a roller refiner and modern conche sounds simple enough. But it must be recognized that this equipment requires additional infrastructure in order to run-it's not as simple as plug and play. Older longitudinal conches can also be used and don't require the same infrastructure, but are hard to find and much less used nowadays.
As well, without an automated closed system to move the products between stages, the process of mixing, loading and moving semi-finished and finished product between machines can be onerous and labor-intensive. Furthermore, food safety risks are greatly increased without a closed system
Both a roller refiner and modern conche require hot and cold water supply to run properly. This means a circulatory water system that provides both hot and cold water on demand. Such a system requires both a hot water heater of some type as well as a chiller to provide a constant supply of cold water.
A basic system for this type of equipment is easily upwards of $15,000 USD, not including plumbing and installation. Because of the size of a roller refiner is usually at least 2-3 feet wide, a hydraulic lift or other setup is often required to properly feed the rolls if product transport is not automated. There are much small roller refiners, but the smaller you go, the less efficiency you have and lower production capacity.
When chocolate liquor is produced in a mill, it is then ready for the next step of processing. While warm and in liquid state, it is mixed with granulated sugar. Of course, this requires a large mixer, which is another additional machine in the process. It is then transferred from the mixer into the roller mill. It also assumes you have some kind of holding tank for your chocolate liquor which is heat jacketed to maintain it in a liquid state.
Roll temperatures are ideally electronically controlled via hot and cold water and temperature control units, which pump water into the inside of the rolls as needed to maintain specific temperatures in each roll. This aids in helping the cocoa mass film adhere properly and efficiently to each roll as it is fed into the machine.
The roller mill provides several quality advantages in processing chocolate. Roll pressure and gap (distance between rolls) are set manually and controlled via internal hydraulics. Roll temperatures are set accordingly. On a three roll mill during the first pass, the sugar and cocoa mass can be reduced to a particle size of approximately 60 to 80 microns. The first pass produces a fairly gritty particle size and can easily be detected on the tongue. The mass of sugar and cocoa mass must then be processed a second time.
The resulting product coming out the mill is called chocolate flake. When examined under a microscope, it has a flake shape where sugar, cocoa solids and cocoa butter have been compressed together through the shearing force of the rolls. Before the second pass, this flake is ideally mixed again before being processed.
On the second pass, roll pressure is increased-the amount of force required to move the roll is increased. Roll gaps, the space between each roll, are decreased. Roll temperatures are adjusted to accommodate the new chocolate flake. The particle size can easily be reduced to under 20 microns in the second pass. While achieving a precise (within 2-3 micron range) is possible, it is challenging on this type of machinery.
Many small makers do use a 3-roll process in refining their chocolate. It produces the most uniform particle size, and if particle size distribution were to be graphed and analyzed mathematically through sampling, we would get a tall bell curve with a normal distribution, with a high concentration of small particles and few outliers (larger particles). This is in contrast to the stone grinding method, which is less effective in uniformly reducing particle size and results in a softer curve and flatter, more hill shaped bell with many small particles within the desired range, but also many more larger particles as outliers, resulting in a different texture and mouthfeel of the chocolate, as well as lower viscosity.
Modern five roll refiners are much more efficient than three roll mills for chocolate production, as they reduce the cocoa mass and sugar mixture immediately down to the desired particle size. Newer five roll mills are computer controlled and have built-in particle size monitors which adjust roll pressure and gap in real time in order to maintain product uniformity and pre-programmed particle size. However, most mills do require manual adjustment and know-how. This requires that the operator not only has an acquired visual sense that the flake coming off the machine is the right particle size, but also frequent stopping and starting during production in order to manually measure the flake coming off the machine and make pressure and gap adjustments when needed.
For the American palate, a particle size near 20 microns provides an appealing mouthfeel. Different countries and regions prefer different textures, which can be achieved by reducing the particle size even further. But at or below approximately 25 microns, it's hard for the tongue to detect much texture or roughness. Below 15 microns, the chocolate will feel pasty or muddy on the tongue, and will adhere to the palate quite a bit, changing the mouthfeel, flavor and viscosity.
A well recognized operations expert in the chocolate industry once remarked to me that using a 3-roll mill to make chocolate is akin to driving a high end vehicle into the ocean. It simply is not the ideal piece of equipment. This is not to say that it can't be done. Three roller mills continue to be used regularly in the craft chocolate industry, but from an operations perspective it's just an inefficient and frustrating way to make chocolate.
Both three and five roller mills require expensive infrastructure to operate, and to make sense financially they require a high utilization rate due to their high investment cost. Ideally, they should be part of a closed, automated system that operates at high volume. From a food safety perspective and for cost considerations, this is the ideal system and is how most industrialized chocolate plants operate. Craft chocolate makers have adapted the equipment to meet their needs, with few sacrifices for quality but occasionally compromising other production factors.
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