The first thing we did during my cooking session with Yamada-san was the most fundamental: Prepare a dashi. Dashi is the foundation of Japanese cuisine, the basic stock that infuses Japanese dishes with its distinctive, savory, umami-flavor. There are a number of dashi, but the classic one is prepared from kombu and katsuobushi -- an edible kelp and dried, tissue-thin shaved bonito, both naturally preserved ingredients, both among the most umami rich foods on the planet. I'm going to explain how Yamada-san prepared his dashi, then get into detail about things he explained and I observed during the process. Dig into it as much as you'd like.
Dashi preparation is a process of extraction and infusion. You extract the flavors of kombu by steeping or heating in water, then infuse the liquid with katsuobushi (K.B. in my shorthand). Classically, you prepare two versions of the dashi when you cook it, the first and the second (ichiban dashi and niban dashi). Ichiban dashi is a delicate, fleeting stock meant for clear soups (suimono), while niban dashi is an all-purpose stock to cook with. Although our goal was to prepare dashi for cooking, Yamada-san walked me through the two-step process, so I could understand it. It's actually pretty straightforward, although as I'm writing it, I realize it might seem complicated at first blush. Be not afraid. Here's how he did it:
4 cups of water
1 piece of kombu, about 5 inches long
2 handfuls of K.B. (this estimation works), plus 1 more handful
Set up a large strainer that fits in a mixing bowl that can hold at least a quart of water. Line the strainer with cheesecloth and set aside.
Add the water and kombu to a saucepan and let it sit at room temperature for 30 minutes. Place the saucepan over medium heat and simmer until just before it starts to boil (you'll notice bubbled forming on the bottom of the pot). Remove the kombu and set aside. This steeping and heating process will extract maximum flavor from the kombu.
Once the kombu has been removed, bring it to a boil. As soon as it boils, turn off the heat. Remove any scum that has accumulated on the surface (impurities from the kombu). Now, add 2 tablespoons of cold water to the liquid in the saucepan to cool it. If the water is too hot when you add the K.B., you'll release its impurities and damage the flavor. You want the temperature to be about 70 degrees C (or 160 degrees F). You can use a kitchen thermometer, if you'd like, or just guestimate it -- when it cools about a minute, it'll be ready.
Now add 2 handfuls of K.B. Allow the K.B. to infuse the liquid. Do not stir, but you can gently push the K.B. down into the liquid if necessary with chopsticks. As soon as all the K.B. becomes saturated, gently strain it through the cheesecloth. Do not squeeze or push down on the ingredients while you strain, which will cloud the stock. When all the liquid has been strained, look at the stock. Taste the stock. Smell the stock. Notice its deep golden color, lip smacking umami, and alluring smoky fragrance? You've now got yourself some ichiban dashi.
To make the niban dashi, return the used K.B from the strainer to the saucepan. Add the reserved kombu you used earlier. Pour in 4 cups of water and place over medium heat. Bring the liquid to a boil. As soon as it boils, turn off the heat and add a handful of fresh K.B. Let it steep for a few minutes. Meanwhile, set up the strainer and cheesecloth (use the same cheesecloth as earlier) in another mixing bowl. After about 3 or 4 minutes, strain the liquid. This time, squeeze the ingredients in the strainer and wring the cheesecloth to yield as much liquid as possible. This is your niban dashi. You'll notice the color, umami and fragrance isn't as intense as the ichiban dashi, but this stock has plenty of umami to cook with.
Okay, so let's get into some details now. First, with the niban dashi, you can bring it to a boil because it's not as subtle and refined as an ichiban dashi, so not as delicate. Also, the handful of K.B. we add to the niban dashi is called oigatsuo, or "chasing katsuo." This, of course, intensifies the K.B. flavor and umami of the niban dashi, and is a technique you'll see soon for other cooking liquids.
A few things about kombu: Yamada-san brought with him a longish piece of ma-kombu, a fine variety. It had a thicker tapered end, and a wider, thinner end. It certainly looked like a frond of kelp. What Yamada-san explained was that the tapered end was the root side of the frond, which produces too strong a flavor for dashi (it has other uses). So he broke off a piece from the wider frond. Also, the kombu had a whitish substance on its surface. That's a critical umami compound, Yamada-san explained, adding that you don't want to wash or rinse the kombu before you use it, which would wash away this umami. I know some older cookbooks advise washing kombu, but today Japanese kombu is basically packed clean, like packaged baby arugala or something, so you can use it right out of the bag.
While the method above instructs to steep kombu for 30 minutes then gently heat, Yamada-san shared two other approaches. First, you can simply let the kombu steep in water for 12 hours, remove the kombu, then heat that liquid to 70 degrees C and add the K.B. Another approach, which apparently has been proven by scientific research to yield the greatest concentration of kombu umami is to add the kombu to water and heat to 60 degrees C and carefully simmer hold that liquid temperature steady for an hour. This is the latest kombu extraction innovation, but it's more geared for fancy restaurant fare.
Like everything in Japanese cuisine, you can go as deep as you'd like with dashi, or not. Depends what you're cooking for. I'm sticking with Yamada-san's method above, which is perfect for my kind of cooking, and simple, to boot.