Chocolate Coating in Belt Coaters
There are several factors to consider when trying to model coating times
- At the end of the coating process the chocolate coating must be largely crystallised, otherwise it will soften as latent heat is released after coating
- Chocolate for coating is untampered hence it will crystallise more slowly than would tempered chocolate. However there is some evidence of mechanical agitation of liquid chocolate as it cools in generating desirable crystal forms
- There are two phases of cooling/heat removal for each coating
- Initial immobilisation of the surface chocolate by cold air, essentially removing only sensible heat
- Removal of latent heat from previous, immobilised coats as the fats crystallise. The rate of this heat release will itself be dependent on several factors and modelling it precisely is virtually impossible. The latent heat will release fairly slowly but the balance of latent heat release, heat transfer through the liquid and immobilised chocolate and heat removal from the surface is very complex
- The fat combination of the coating (increased milk fat reduces the rate of crystallisation of cocoa butter/milk fat mixes)
- The temperature of the immobilised coating – chocolate fats crystallise more slowly below about 15°C. However as the fats crystallise and release latent heat this will increase the local temperature and rate of crystallisation until it reaches about 20°C when crystallisation will stop
- The latent heat present in the fats is sufficient to raise the temperature of the immobilised chocolate in each coat by about 30 degrees C, so has to be removed
- This latent heat has to transfer to the cooling air by conductive heat transfer through the later solid and liquid layers
- Heat released during smoothing and removed during the final cooling phase before discharge will be largely latent heat with some additional heat generated by friction
- The first coat will be onto cold product and therefore not solely dependent on heat removal by air, so a relatively large amount of chocolate can be added at this stage
- Subsequent coats will see released latent heat reducing the cooling effect on the liquid chocolate, so as the amount of latent heat release increases so the amount of liquid chocolate which can be added per addition will reduce, hence the following curve.
- If the automatic control system is set up purely on the basis of the final coat time (which it must be) then the initial coats will be relatively conservative