2: This whitening of the mixture happens because by beating, you incorporate thousands of tiny air bubbles into it.
3: Add 6 tablespoons sweet white wine to mixture (or sweet wine, fruit juice, coffee, etc.) and 1 pinch flour, mix thoroughly. Please note, this pinch of flour is vital to the success of the sabayon. While over the bain-marie, this will facilitate the blending of the mixture: an essential knack to make your sabayon work every time (or almost), so you do not finish up with an omelette... This is the first "secret" of success.
4: Put mixture in the bain-marie, and begin beating. The bain-marie is the second "secret" of success, you need the temperature of the mixture to rise gradually. You need to beat constantly until obtaining the shiny and smooth mixture desired.
5: You can use an electric whisk, in which case do not beat too fast, but nothing is better than a simple hand whisk, you will keep operations under control.
6: After few minutes, the mixture will begin to foam and thicken.
7: Stop when you like, it is necessary to arrive at a good compromise: quite shiny and very smooth... It's an absolute delight!
Remarks
The two important points for making a good sabayon are: a pinch of flour (for easier blending) and a bain-marie (gradual rise in temperature). Syllabub is often poured over a dessert, but you can also serve it plain in a small cup (warmed beforehand) instead of coffee or tea. Syllabub is best served warm, on something which should be neither too hot ( not straight from the oven), nor too cold (not straight from the fridge). This recipe is for a sweet syllabub but it can also be made savoury (see above). You will notice that in this case, because of the absence of sugar, the syllabub thickens much more quickly.