Students taste samples of the chocolate that have been melted and re-hardenend and samples fresh from the packet and compare the taste and physical properties.
Technician preparation before the lesson may be needed if pre-melted and set chocolate is required. Any milk chocolate is fine for this practical. Dairy Milk and similar types can be purchased in big bars and only a couple of squares per student are usually required.
For pre-melted chocolate, take a sealed packet and place on a radiator or warm place until soft and re-harden by placing in a food refrigerator. Once set, remove and store at room temperature. Ensure that the re-hardened chocolate is the same make as the other samples.
Equipment required (per set):
The re-hardened sample is investigated in the same way and melting point and physical appearances noted.
The two samples are compared after results and observations recorded.
The fresh sample should melt at around 32-36°C. (form 4 in the table below).
The re-hardened sample should melt at a lower temperature (form 2-3 in the table).
During chocolate manufacture, the cocoa butter can solidify into one of six polymorphs listed in the table below. A form 5 polymorph can be found in the best tasting quality chocolate. Other forms may feel sticky and unpleasant when eaten.
| polymorph | melting point (°C) | comments |
|---|---|---|
| form I | 17.3 | Produced by rapid cooling of melt. Successive polymorphs are then obtained by heating at 0.5 °C/min. |
| form 2 | 23.3 | Produced by cooling melt at 2 °C/min or rapid cooling of melt followed by storing from several minutes up to one hour at 0 °C. This form is stable at 0 °C for up to 5 hours. |
| form 3 | 25.5 | Produced by solidification of melt at 5-10 °C or transformation of form 2 by storing at 5-10 °C. |
| form 4 | 27.3 | Produced by solidification of melt at 16-21 °C or transformation of form 3 by storing at 16-21 °C. |
| form 5 | 33.8 | Produced by tempering (cooling then reheating slightly while mixing). The most desirable form with good gloss, texture, and "snap". |
| form 6 | 36.3 | The transformation of form 5 after spending 4 months at room temperature. Leads to the white, dusty appearance. |
The contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.