* Why choose butter?

Butter has a natural composition based purely on milk and defined by law. Other fats (such as margarine) are blends of vegetable oils and animal fats. Butter has the same calories as these other fats, but it's the flavour that makes it a real winner. It's extremely tasty and it really brings out the best in other foods.

* What temperature should butter be stored at, and for how long?

The best storage temperature is between 0 and 8°C, which is the same as the special compartments in the fridge, which ensures the butter is never too hard. It can be kept in the fridge for 2 weeks, bearing in mind its best before date.

* Does butter absorb smells?

Yes, it can do. In the fridge, it should be well covered or kept in an airtight container.

* Why does butter melt ?

Butter, like margarine, contains around 82% fat with around 18% being an aqueous phase. The aqueous phase in butter is practically skimmed milk. Depending on the product, this aqueous phase may contain some salt (1 to 2% of the finished product).

The structure of butter and margarine is actually an emulsion: because it does not dissolve in the fat, the aqueous phase is dispersed in the form of tiny droplets throughout the fatty phase. The fat is therefore the "continuous phase" of the emulsion: it's what you see (butter is fatty to the touch). It is a partially crystallised solid emulsion (the crystals are very small and not visible). It is the combination of fat in a liquid state and fat in a solid state that gives butter its malleable texture. The colder the butter, the more it crystallises and the harder it becomes.

The combination of fat crystals and liquid fat is explained by the fact that all fats are biological substances comprised of a range of compounds (glycerides). At a given temperature, some (the saturates) are solid, having crystallised, while others remain liquid (the unsaturates); these can solidify but at lower temperatures (freezing, etc).

Depending on the nature of the fat (more or less saturated), crystallisation and therefore solidity will be more or less intense at a given temperature. If you refrigerate olive oil or groundnut oil at 4°C, you will see partial crystallisation in the oil (appearance of white flecks).

NB : with cream, it's the other way round: the milk fat is dispersed in the skimmed milk (the droplets are made up of fat). Even in the fridge, the cream remains liquid even though the fat it contains is partially solidified.

The physical phenomenon of crystallisation is an ordered arrangement of a product's components. You find it in water when you bring it down to a temperature below 0°C. As it is a pure substance (it only contains water molecules), crystallisation is total below 0°C and the water is solid.

Fusion is the inverse phenomenon to crystallisation. When you heat a (solid) crystallised product, it liquefies. If it is a pure substance, like water, total fusion is realised at a precise temperature (0°C for water); the water passes from 100% solid to 0% solid at 0°C. For a fat, this fusion happens over a much wider temperature range (often tens of degrees). Within this temperature range, the fat is more or less solid. Above this temperature range, the fat is completely liquid and flows freely: this is the temperature of fusion, or rather the end of fusion (for butter, this temperature is 32°C).

NB : when water is impure, there is also a fusion range; as with ice cream containing sugar, milk components, etc that is not 100% solid at -18°C; it has a fusion range from below -18°C to 0°C.

Should you have any other questions ? Please feel free to send tem by mail.