It is really a physics problem involving the interaction of water with a carbohydrate, and the process differs from food to food.
When you have a solid food that you want to be able to cook faster, such as rice, you hydrate it, then dehydrate it under controlled conditions, adjusting the chemistry and physics of the particle to maximize its ability to rehydrate. Then when you rehydrate it to cook it, it cooks much faster.
For many foods, the processing involves increasing overall surface area, so the water does not take so long to migrate through the food.
For tea and coffee, it involves agglomerization, building up the particle size so the surface area increases dramatically, which makes it easier for water to be absorbed.
For some products, sugar or another hydrophilic (water-loving) additive is mixed in to speed absorption. For noodles or dried vegetables for instant soup, the process may involve quick drying in a vacuum, which puffs up the food so it will rehydrate more quickly.
