Dashi is to Japanese cuisine what chicken stock is to French cuisine. It is clearer and thinner than stocks used in Western cuisines, with a distinct saltiness and umami-rich, flavour of the sea which underpin a lot of the country's national dishes. Dashi can be made fresh, but instant granules are a key ingredient in the Japanese cook's arsenal, as the stock is often used as the base of soups or dipping sauces.
Traditionally, families made their own dashi at home. To do this, a big pan of water is brought to the boil. Dried kombu seaweed, and dried bonito (fish) flakes are then steeped in the gently simmering water, and strained. As with tea leaves, the dried seaweed and fish flakes can be reused — but will create a weaker 'brew'. The stronger, first-brew dashi is known as ichiban dashi, and the second, weaker brew is called niban dashi.
The downfalls when it comes to making dashi from scratch are the cost of bonito flakes and the time investment means that it's often cheaper and more efficient to use instant dashi granules. Instant dashi is often sold in 5g sachets, which can be torn open and stirred into hot water - as with powdered stock. The granules can also be bought in larger pots, and occasionally in pre-mixed sachets of liquid stock. These can be found in some large supermarkets, as well as Japanese speciality food shops.