A week of miso soup, day 1: Zucchini miso soup

Continuing my series on Japanese home cooking, this week I would like to introduce different kinds of miso soup. Miso soup (misoshiru) is one of the key parts of a Japanese meal. Another kind of soup that is served often is a clear soup called osumashi, but the miso soup base is more adaptable to all kinds of variations.

The components of a miso soup are quite simple. It's based on a soup stock called dashi, with various ingredients cooked to different degrees in it. The miso is added at the very end of the cooking process.

I have gone over the making of dashi stock before (as well as the basics of miso soup), but it's always worthwhile going over it again - this time with pictures! I've given some vegetarian options for dashi also.

Today's miso soup is not quite traditional, but it's very easy to make with an ingredient that's easy to get practically anywhere. Besides, zucchini are very much in season right now, as anyone with a zucchini plant in their garden knows.

(If you haven't already, you may want to take a look at the essentials of a Japanese pantry, which has an explantion of the ingredients used.)

Traditional dashi stock

This is a basic and very delicious dashi stock, made with just two ingredients, pictured here.

The dark things are dried sheets of konbu seaweed that I have cut up with scissors for ease of use, and the stuff that looks like wood shavings is shaved dried bonito flakes. I store both double-bagged in plastic bags in the freezer.

Konbu is a large, thick leathery seaweed that is bursting with minerals. What makes it so ideal for making stock from is that it's packed with umami. Dried konbu will have a fine white powdery substance on the surface. Don't wash that off - that is full of umami! Some instructions may tell you to wipe off dirt from the konbu, but to be honest I haven't seen konbu with dirt on it for years, especially not on the dried, pre-packaged kind you are likely to find. If you taste it you will see that it is sort of like a much subtler version of MSG (monosodium glutamate) - not surprising, since MSG is actually chemically isolated umami.

Bonito is a kind of fish (called katsuo in Japanese); it's a popular sashimi item. A whole bonito fish side is slowly dried until it becomes a hard, woodlike block called katsuobushi. This is then shaved thinly. In my grandmother's time every household had a katsuobushi shaver, that sort of looked like a wood planer fixed on top of a box. My mother still prefers to shave her own, but I just use the pre-shaved kind that you see in the photo.

To make about 4 cups of dashi stock, you will need:

• 4 cups of cold water
• A 4 inch / 10 cm square piece (or small pieces adding up to that amount) of dried konbu
• About 1 cup (a handful) of bonito flakes

Keep in mind these are not exact amounts. Adding more konbu or more bonito flakes will just give it more flavor. Fans of the original Iron Chef TV series may recall Iron Chef Japanese Rokusaburo Michiba (the one who preceeded Iron Chef Morimoto in that role) adding huge handfuls of bonito flakes to his dashi pots.

First, put your dried konbu and cold water into your pan, and leave it to soak for at least 20 minutes, preferably overnight. Don't wash off that white powder!

After the soaking time, bring the water up to a boil, throw in the bonito flakes, and turn off the heat. Leave to steep for a few minutes, then strain through a sieve.

Your dashi will be a pale golden yellow in color, and ready to use.

Note: if you are frugal, you can keep the used konbu and bonito flakes to make nibandashi from them - a thinner dashi that is fine for use in stewed dishes like nikujaga (Japanese meat and potatoes). Put in a plastic bag or container, and refrigerate for up to 3 days (or freeze) until ready to use.

Alternative ways of making non-vegetarian dashi

The easiest way is to just use dashi stock granules. I always have a box of this around since it's so handy. The amount to use depends on the brand, but generally it's about 1 teaspoon to 4 cups of water. Two brands that are widely available are Ajinomoto Hondashi and Shimaya Dashinomoto; to me they are virtually indistinguishable, though the Hondashi may have slightly more bonito aroma. Do keep in mind that dashi made from granules is saltier than dashi made from natural ingredients, so you will need to adjust the amount of miso soup you put in later. (See also health considerations - most dashi stock granule brands contain MSG.)

In some Japanese households, small dried fish called niboshi are used in stock instead of bonito flakes. You simply throw a few of them into the pot with the konbu, and let it simmer a bit. I have a bag of powdered niboshi, which can be used just like dashi granules. Some people object to dashi made from niboshi, considering it to be too fishy tasting. I don't mind it myself but I do prefer bonito flakes.

Vegetarian dashi

Use my basic vegetarian (vegan) dashi stock recipe. Alternatively, you can use vegetable stock cubes - the flavor won't be totally authentic, but will still add plenty of flavor.

What kind of miso to use

There are basically 2 kinds of miso widely available outside of Japan: white or yellow-brown, and red. For miso soup, I mostly use white miso (shiromiso) or awasemiso (blended miso). See the Japanese pantry list for more about miso.

Making miso soup

The key thing to remember when making miso soup is that the miso is always added last. Miso is quite heat-sensitive, and boiling it vigorously will really affect the flavor and texture adversely. Over-boiled miso soup takes on a rather grainy quality. The only things you can add after adding the miso are things that cook instantly, such as baby spinach leaves.

So, let's make a very simple miso soup.

Zucchini miso soup

• 4 cups of dashi stock, prepared as above using your preferred method
• 1 cup zucchini, cut into thin strips (about 1 small zucchini)
• 1/4 to 1/3 cup white or blended miso (see notes)

Bring the dashi stock to a boil, and add the zucchini. Simmer until the zucchini is tender, about 5 minutes.

Put the miso into a small cup. Add a little of the hot dashi stock, and mix around with chopsticks or a fork until the miso is dissolved into a smooth paste. (The picture on top shows the miso before it's dissolved, and the one below shows it after.) Add to the soup. Taste the soup, and add a little more miso if it seems too weak for you. (I actually do this mixing with dashi part in the soup ladle, but a cup may be easier to handle if you aren't used to it.)

Bring the soup back up to heat, then switch off. Serve immediately.

Notes:

• If you are serving miso soup as part of a Japanese meal centered on white rice, make it a bit stronger in taste; if you are serving it as a separate course, hold back a bit on the amount of miso used. Always taste to make sure you have added the amount that's right for you.
• Miso has a natural tendency to separate from the water/dashi, especially as it cools. If this happens to you, don't worry, just mix up the soup a bit.