The science of whipping cream
Milk is an emulsion, a mixture of two immiscible substances. In the case of milk, fat globules are suspended in an aqueous solution. Since fat is lighter than water, it rises to the top of fresh milk where it is collected as cream. If you've ever had milk delivered to your door and noticed the layer that forms at the top - that's the cream.
Why does cream whip? Cream has a higher fat content than milk. When you whip the cream, you are introducing lots of tiny little air bubbles into the mixture. The fat globules merge together and form a protective layer around each air bubble. This protective layer of fat traps the air in the cream and because the fat globules are now aggregated, it is more difficult for them to move around one another, causing the mixture to flow more slowly and making it thicker.
Why so sour?
When something with a low pH hits our tongue, our brain interprets it as 'sour'. Lemons are a prime example of this. The pH of natural lemon juice is around 2.5 (very low). This is attributed to the presence of citric acid. Citric acid is also produced on a mass scale and is used for a number of functions, including as a popular food additive. It mainly used for its properties as a natural preservative but also as a flavouring, especially in soft drinks, a fat emulsifier and speed up fermentation in commercial-made cheeses.
Bread making involves lots of science. When making the dough, the starch (about 70% by weight of wheat flour) absorbs the water in the dough and then enzymes digest the starch, turning some of it into sugar. Yeast feed off these sugars in the dough, producing carbon dioxide and alcohol as bi-products. Little pockets form in the dough and when the bread is baking, these little pockets expand as their contents evaporate, leaving bubbles in your cooked loaf.
Caster sugar is a type of white sugar with superfine crystals. It originally got its name because the small grains of sugar could fit through the holes of a caster or screen. Nowadays, it is produced on a large scale by grinding down granulated sugar into fine white crystals of uniform shape. Caster sugar is used in special applications such as cake mixtures, puddings and powdered drinks because of its dissolving properties.
In baking, it produces textural differences in the final product by incorporating more air into the mixture, leading to a greater volume and lighter product. Much of the light and tender texture of cake comes from the gas bubbles, which are incorporated into the mixture during a process calling "creaming" - the vigorous mixing of the fat (butter) and sugar. Air is carried along the rough surfaces of the sugar crystals. Caster sugar is used in baking because the smaller the crystals, the more air is incorporated.