Hi Quin, sake isn't added when making dashi. It's usually added when you cook something with dashi, for example if you were to make a Nimono or Beef Udon. As for the type of sake to use for cooking, I have a series of 4 videos on Youtube explaining everything you'll want to know and the first part is here: https://youtu.be/C2p6MN4EVeA

Hi Gerrit, it's been over a decade since I've been to Europe, so I'm not sure what the availability of ingredients there is like right now. You're best bet is to check Japanese grocery stores either in person or online. Since Niboshi is a dried product I'd guess there's a fairly high likelihood of finding it in a Japanese grocery, but I know things like katsuobushi are restricted due to the way in which it is processed.

Hi Adeline, yes it's possible, but it would be missing a major component. Konbu is rich in glutamate, a type of amino acid. Katsuobushi is rich in inosine monophosphate, another amino acid. When you combine them the effect is like 1+1=3. Either one on their own does not provide the full experience. It's kind of like listening to a recording of a symphony on a very small speaker that doesn't have any bass. You'll get the gist of the song, but it won't sound right.

Hi Eline, in my experience boiling the dashi does not make it bitter. There are two main reasons not to boil the konbu in the dashi. The first is that konbu can release slime when boiled, which can make your stock a little viscous (but with the amounts I add to my dashi this isn't a big deal). The second issue is that boiling the konbu releases the flavor of the konbu into the dashi. This is not ideal when you're trying to make a very delicate dashi as it will make it taste like kelp. The purpose of the konbu is really to increase the amount of glutamate in the dashi so ideally you don't want to taste the konbu. That being said, unless you are using very expensive ingredients, the difference is negligible, so I wouldn't worry too much about it. Also, once you remove the konbu and katsuobushi you can boil the stock as much as you want without worrying about extracting off-tastes from either ingredient into the dashi.

So glad to hear it! Thanks for stopping by to let me know!