Tempering is the process of gently heating and cooling chocolate to stabilize the emulsification of cocoa solids and butterfat. This technique is generally used by professionals with couverture chocolate. It allows the chocolate to shrink quickly (to allow easy release from a mould, for example with Easter eggs) or to be kept at room temperature for several weeks or months without losing its crispness and shiny surface. All solid chocolate is tempered in production, but once melted loses its ´temper´ and must be re-tempered unless it is to be used immediately.
Untempered chocolate tends to â€˜bloomâ€™ or becomes dull and streaky or takes on a cloudy appearance. This can be avoided if melted chocolate is refrigerated immediately as chilling the chocolate solidifies the cocoa butter and prevents it from rising to the surface or ´blooming´. General baking and dessert-making do not require tempering, which is a relatively fussy procedure and takes practice. However, it is useful when preparing sophisticated decorations, moulded chocolates or coatings. Most shapes can be made without tempering if they are refrigerated immediately.
* Melt the couverture chocolate by the preferred method â€“ the microwave method is quick, easy and the least messy. The temperature should be about 45C/110F. Stir to be sure the chocolate is completely melted and smooth.
* Pour about three–quarters on to a marble slab or baking sheet and, using a metal palette knife or rubber scraper, quickly scrape into a pool in the centre and then spread out again. Work the chocolate for 3-5 minutes until no streaks remain. Scrape back into the chocolate remaining in the bowl and stir until blended. The temperature should be about 32C/90F. The chocolate is now tempered and easy to use.
(Source – Irresistible Chocolate by Elizabeth Wolf–Cohen)