Daikon Simmered with Canned Hotate (Scallops)
with Blanched Komatsuna on the side
When making a simmered dish with daikon radish, it is generally recommended to pre-boil it with a little amount of raw rice or in rice rinsing water until a toothpick can be inserted easily. It is a well-known tip here in Japan, but most of us do not know the scientific reason behind it (or if there is one at all). So, having been triggered by a question from someone who read my buri-daikon post, I did a bit of net research. Let me share the result with you.
In a nutshell, the pre-boiling process mentioned above is supposed to remove the slight bitterness or harshness of daikon and make simmered daikon soft and tasty. They say that adding rice, or using rice rinsing water for this process means boiling daikon in a colloid solution, and the bitter substance contained in daikon will be adsorbed onto the colloidal particles during this process.
If a colloid solution is the key, then can’t we just add regular wheat flour or corn/potato starch in place of raw rice? Well, some Japanese websites say that a little amount of wheat flour will do, but I found one person saying that it’s not a good idea because wheat flour contains some protein (but didn’t really mention how that protein negatively affects this process). And more than three people wrote that if used potato starch, the simmering water will turn into glue, which I totally agree with. (I mean, if used too much of it.)
On the other hand, some people do say that using raw rice or rice rinsing water is not necessary; pre-boiling in regular water is just fine. Or some even say that pre-boiling is not necessary at all because these days daikon radishes do not have such strong bitterness. Confusing, isn’t it?
What I do -- as a sort of compromise solution-- is: do pre-boiling for simmered daikon dishes with light seasoning, and skip it for those with heavy seasoning. To me the best example for the former is furofuki-daikon, and the latter is oden or buta-bara daikon (daikon simmered with pork ribs). I put buri-daikon (daikon simmered with yellowtail) in the former category, because the fish has the risk of giving an unwanted fishy flavor to the dish, so I don’t want any additional unwanted flavoring from the daikon. Personally, I believe that this pre-boiling trick makes a big difference when you want to enjoy the delicate taste of daikon itself with light seasoning.
Now, I was also asked for a tip to avoid bitter daikon and choose good ones. But sorry, I still cannot find an answer. The problem was that there were many websites talking about the “pungency” of daikon, but not exactly about the “bitterness.” They say that the pungency is caused by a substance called isothiocyanate, and its precursor substance is contained more in the tail end and near the skin. Thus, there are ways to deal with the pungency; advices about which part is suitable for what kind of dish are available almost everywhere. Now what I don’t know is whether the bitterness is caused by the same substance, isothiocyanate, or not. My hunch is probably “No,” because simmered daikon can be bitter without any pungency.
Then I have no idea if there is a way to avoid certain bitter parts in a daikon or tell bitter daikon from non-bitter ones. Harvest season or fertilizers used may make some daikon more bitter than others, but how can you check out such information when buying one at the store? So all I can say is, "To choose good daikon, choose fresh ones. And if worried about bitterness in simmered daikon dishes, don't skip the pre-boiling." That's about it. Sorry.
As for the softening effect, some say that an enzyme contained in rice bran makes daikon soft, though I couldn’t find any site clearly mentioning the name of the enzyme. But in my experience, daikon did soften quicker when a little amount of rice or rice-rinsing water was used for pre-boiling.
So, to me this pre-boiling technique is not a mere old-wives tale, but some of the seemingly scientific explanations seem pretty wishy-washy. That’s the way I see it. And I don’t really need to find out the ultimate truth of daikon boiling anyway. What’s more important for me is the feeling of warmth and happiness that a tasty winter dish brings to me…
** Just in case:
After chopped daikon are "pre-boiled"with raw rice or in rice rinsing water, they need to be drained, rinsed with running water and then cooked in water and seasonings. You don't want to use the colloid solution from the pre-boiling for cooking and seasoning the daikon, of course.