Hi, Chau. On what do you base this?
I rotate between 5 different starters, so I encounter plenty of hooch. I used to always pour it off. Now I always stir it back in. I think my starters are more flavorful and predictable now, but I've never done side-by-side tests. Curious as to why you say this. Maybe I've been doing it wrong all these years!
Bill, I haven't done extensive testing or side by side testing and it's really based loosely on my experience and preference for a light sourdough taste and not a heavy one. From what I've seen, starters typically develop more and more acids as they become mature. Hooch develops long after a starter has fallen with the acids destroying the gluten matrix and releasing the majority of the water. That hooch can contribute added flavor in form of acids, fermentation byproducts and what have you, but it's not going to contribute any more flavor compared to pouring the hooch out, and refreshing your (overly acidic) starter with more water and flour (less than the amount of existing acidic starter). There are already plenty of acids and flavor in a overly mature starter as it is. IMO, the hooch only adds excess acids that are detrimental to the the dough, if a large % of your dough is starter. If you don't watch the dough carefully, these acids break down the gluten matrix leading to an overly sour loaf and a dense crumb. I guess that can be ideal for some folks, so I shouldn't say it's absolutely wrong.
Bill, what percentage of starter are you typically using? If you are mixing in only a small amount (say 1-5%) starter, it matters less if the starter is overly acidic or too hoochy ( I think this is a word), because the acids are diluted out to a point of not being a noticeable detriment. If you tried to make a dough with 50% overly mature (acidic) starter with hooch, then you will see the negative effects quite readily.
So, for me hooch is bad and doesn't make sense. Why do we dump half (or more of starter) and refresh anyway? What is the purpose of this exercise? Because when you do dump, you are actually dumping out flavor (acids, metabolites, etc). Why not just take a starter from the fridge with all of it's hooch, stir back in, and use it as is? What kind of result can we expect? What will we get? and why?
So what's the big deal about stirring back in the hooch anyways? What is the effect of that? It's not a huge deal, but it will (in theory) delay your reactiviation time or time until the starter is ready to be used. Of course this also depends on how much starter you use to start with and what point one deems it ideal to use a starter. If one were to retain or use 1% of the old starter versus 50% (of the old starter) in the new starter batch, it would take much longer. In this case, hooch has little effect. But in a 50% scenario, hooch has a much bigger effect. The acidic environment (I believe) slows down yeast activity. So how detrimental hooch is depends on how much is used. In general, I don't think it's a good thing, but it doesn't have to be wrong either per se.
This has just been my experience, but I would love to hear other theories out there.