How Do Raisins Get Their Colours?
Raisins – be it dark brown or golden -are anytime munchers. Do you ever wonder how they get those colours?
Cutesy in shape and candy-sweet to taste, raisins – either dark brown or yellow/golden – are immediately and universally accepted to the palate. While munching then, are you ever given to thinking how do raisins beget their colours? Is it different grapes? Or is it different processes?
A Grape Start
All raisins start out as grapes alright, but there are specific types of grapes that are particularly cultivated to convert them into raisins, just like a typical species of grapes, reared to be consumed only as fruits. The most common species of grapes used to make raisins are called the Thompson seedless.
Sunning To Preserve
Soon after the relevant grapes are harvested and thoroughly washed, they are spread over mats and or beds under direct sunlight. Kept so for about a couple of weeks, they gradually lose their moisture – which constitutes about 75 % of their total weight and shrivels up. In a raisin, the moisture content amounts to only 15 % of the overall weight.
Come to think of it; this transformation process is a great way to preserve the grapes for a long time. Left on its own, grapes can remain fresh for only a couple of days, but as raisins, their longevity extends to months on end. That is so because microorganisms find it impossible to grow in such a low moisture environment. To compare, the water activity of raisins is about 0.5 – 0.6 point to that of above 0.9 of fresh grapes.
Change in Colour
While the water content of the raisins are being depleted during the drying process, the effects of heat from the sun also causes a chemical transformation. Known as, the enzymatic browning process which is triggered by the enzyme Polyphenol Oxidase (PPO), it is this chemical reaction that colours the raisins.
You might have even observed a variation in the brown colour spectrum. If the raisins dry out faster under hotter conditions, they go to the darker shade. Slightly slower drawing under an easy sun gives them a light brownish tint.
What About Golden?
This is achieved when, prior to sun drying, the grapes are bathed in a Sulphur Dioxide (SO2) solution. This Sulphur Dioxide coat inhibits the enzyme browning process from taking place by deactivating the PPO enzymes irrevocably. Because it has to be chemically treated, golden raisins are always dried mechanically. Regular ones can also be mechanically processed, getting ready in two days instead of a few weeks.
There’s no discernible difference except in texture. Golden ones may be little plump and juicy, while the other will be a little dry and more caramelized.