Or an exotic particle field that eliminated anything that *wasn't* bayronic from the structure held inside it.
Or they're taking for granted that anyone sane understands they're removing the unwanted baryons while keeping the ones that are actually needed.
The vast majority of the ship is made from them, they tend to vary only by the quark combination, a singular field that swept rather quickly through such a dense ship would likely only be removing smaller particles like fermions and such from it.
The whole array was a gimmick and a bad one, an essential process that apparently makes the ship not lethal that it must put into an incredibly specialised station for every 3-4 years or so.
That's never been needed before in older ships, or but smaller vunerable ones like Voyager. A ship that could traverse much more dangerous regions at high warp for decades without needing it.
And that the Enterprise-D only needed to visit it once and never again.