upright=1.35|thumb|Conche (in the [[Imhoff-Schokoladenmuseum)]]
thumb|Granite roller and granite base of a conche
Conching is a process used in the manufacture of chocolate whereby a surface scraping mixer and agitator, known as a conche, evenly distributes cocoa butter within chocolate and may act as a "polisher" of the particles. Since the process is so important to the final texture and flavor of chocolate, manufacturers keep the details of their conching process proprietary.
The conching technique was introduced in Switzerland in the late 19th century. Conched chocolates were distinguished from ordinary chocolates with the French adjective fondant or crémant.
History
Rodolphe Lindt invented the conche in Bern in 1879. It produced chocolate with superior aroma and melting characteristics compared to other processes used at that time. The Lindt chocolate company states that Lindt (perhaps mistakenly) allowed a mixer containing chocolate to run over a weekend (or possibly overnight, according to other variants of the possibly apocryphal story). Upon returning to the device, Lindt recognised the final product to have a smoother texture and greater shine than conventionally processed chocolate of the time. Lindt's invention made the mass-production of chocolate bars more practical, eventually replacing chocolate beverages as the primary means of mass chocolate consumption. The adoption of conching also generalized the use of additional cocoa butter in the chocolate production; until then, molded chocolate often simply consisted of cocoa mass and sugar.
The original machine used by Lindt was developed in the early 1800s by an Italian chocolatier named Bozelli. The Bozelli grinding process was based on ancient Mesoamerican practices of grinding cocoa beans on curved stones, which were called metates.
Lindt's original conche consisted of a granite roller and granite trough; such a configuration is now called a "long conche" and can take more than a day to process a tonne of chocolate. The ends of the trough were shaped to allow the chocolate to be thrown back over the roller at the end of each stroke, increasing the surface area exposed to air. A modern rotary conche can process 3 to 10 tonnes of chocolate in less than 12 hours. Modern conches have cooled jacketed vessels containing long mixer shafts with radial arms that press the chocolate against vessel sides. A single machine can carry out all the steps of grinding, mixing, and conching required for small batches of chocolate.
The conching process remained mostly a trade secret until the end of the century. In the 1890s, Cailler launched a similar chocolate. A long conche was manufactured by J. M. Lehmann from 1899.
Process
thumb|A [[The Hershey Company|Hershey conche from the early 1900s, on display as part of the Hershey Story collection]]
Conching redistributes non-fat solids from cocoa, sugar and milk (that create flavor) into the fat phase from cocoa and milk fat. Air flowing through the conche removes some unwanted acetic, propionic, and butyric acids from the chocolate and reduces moisture. Even a small amount of moisture greatly increases the viscosity of the finished chocolate, so machinery is cleaned with cocoa butter instead of water. Some of the substances produced in the roasting of cocoa beans are oxidized in the conche, mellowing the flavor of the product.
The temperature of the conche is controlled and varies for different types of chocolate. Generally, higher temperature leads to a shorter required processing time. Temperature varies from around for milk chocolate to up to for dark chocolate. The elevated temperature leads to a partially caramelized flavor and in milk chocolate promotes the Maillard reaction.
The chocolate passes through three phases during conching. In the dry phase the material is in powdery form, and the mixing coats the particles with fat. Air movement through the conche removes some moisture and volatile substances, which may give an acidic note to the flavor. Moisture balance affects the flavor and texture of the finished product because, after the particles are coated with fat, moisture and volatile chemicals are less likely to escape.