Tempered chocolate snaps when you break it, shines when it sets, and melts cleanly on the tongue. Untempered chocolate bends instead of snapping, looks dull or streaky, and can develop white bloom as it sets. The difference is not the chocolate but the crystals inside it: tempering arranges the cocoa butter into stable crystals, and skipping it leaves unstable crystals that make a mess of an otherwise good recipe. This calculator gives you the three temperatures that make tempering work for your chocolate type. It also gives the seed amount for your batch weight, so you do not have to guess how much solid chocolate to stir in at the cooling stage.
The three temperatures are melt, cool and reheat. Dark chocolate melts to 50 degrees, cools to 28 degrees while stirring, and reheats gently to 32 degrees for working. Milk chocolate melts to 45 degrees, cools to 27, and reheats to 30. White chocolate melts to 43 degrees, cools to 26, and reheats to 29. White and milk chocolate use lower temperatures because they contain milk solids and less cocoa butter structure, so they scorch and seize more easily than dark chocolate.
Here is a worked example. You have 300 grams of dark chocolate. Melt two thirds of it, about 200 grams, gently over a bowl of simmering water or in short microwave bursts, stirring often, until it reaches 50 degrees. Take it off the heat and stir in the remaining 100 grams, which is the seed, until the mixture cools to 28 degrees and the seed has mostly melted. Then warm it gently back to 32 degrees, remove any unmelted seed pieces, and it is ready to use for dipping or moulding.
The seed method is the easiest tempering method for home cooks, and it is what the calculator supports. The seed is solid tempered chocolate added to melted chocolate, and its stable crystals teach the melted chocolate how to set. That is why the seed must itself be good tempered chocolate, not old bloomed chocolate from the back of the cupboard. The calculator sets the seed at 25 percent of your total, which is enough to cool the mixture and seed it without leaving large unmelted lumps.
Water is the enemy of tempering, and even a small splash can ruin a batch. A single drop in melted chocolate makes it seize into a thick, grainy paste, because water binds the sugar and cocoa particles together. Keep bowls, spoons and thermometers completely dry, keep steam from the water bath out of the bowl, and do not cover hot chocolate with a lid that drips condensation back in. If chocolate does seize, it is not wasted: stir in warm cream and use it as ganache instead.
A thermometer is not optional for reliable tempering. Guessing temperatures by touch or by eye works for experienced chocolatiers who have done it hundreds of times, but for everyone else it produces inconsistent results that look fine until the chocolate sets dull. A cheap digital thermometer pays for itself in one saved batch. Stir constantly at the cool stage, because stirring spreads the crystals evenly and stops the edges from setting before the centre cools.
Use this calculator for every batch, and test before you commit. Dip a knife or a spoon in the tempered chocolate and let it set for a few minutes at room temperature: properly tempered chocolate sets firm and shiny within about 5 minutes. If it stays soft or streaky, re-temper rather than pouring it into moulds and hoping. Tempering rewards patience, and the snap of a well-tempered bar is worth the extra ten minutes.