I don't know that this will be of much help because I don't remember
specifically hearing that term "open-knit," but it surely makes sense.
People have talked of "tightly knit" things, including wines, for many
decades. Part of the quest for language for experience not occurring
naturally in words. (Such idiom can float around among wine people for many
years before someone bothers to catalog it in print or online --
insightfully, if you're lucky -- and it is unlikely ever to have precise,
universally agreed meaning.) Do not expect too much of online wine
glossaries.

After a tasting that I reported here in a recent TN I was driving back with
a wine merchant who told me he would need to translate his personal tasting
notes -- the kind I posted here -- to professional tasting notes, as
meaningful as possible to other readers. A challenge that some people have
a knack for. Some words heard often from specialists in tastings may be
unhelpful to a large readership -- grip, "reduced" sulfur, oxidation,
minerality, Brett [topic of certain notorious, laborious argument threads on
HTML sites], alcohol ["don't ALL wines have alcohol?"], extract. (To say
nothing of those noses who will correctly identify where the barrel wood was
cut from, after sniffing the wine. Seeing this for real is very cool.)

As to "open knit," not knowing that term specifically, I'd infer it a
response to the established "tightly knit." Which does seem apt for some
wines. Like a tightly knit fabric, they are closed, impenetrable. Maybe
the parts work together to give the wine structure to age well in the long
run. In contrast there is much demand for wines of a different kind, wines
made for today rather than tomorrow.

-- Max