The film is about two deteriorating relationships between three women, with director Bronstein serving as the common denominator in the role of Rachel. The other two women are Gen, a sorta-hippie/extrovert played with jittery aplomb by indie darling Greta Gerwig, and Alice, an introvert played by Amy Judd like a turtle in need of a shell. That last sentence might make the two seem like polar opposites, and in a superficial way they are. More interesting, however, is what they have in common.
Both Gen and Alice are extreme personalities, brought to life by bravura performances that embrace that extremity while leaving room for nuance. Gen pushes people away by being obnoxiously "on" all the time, Alice by refusing to converse, to go out, to wash herself or her clothes. Neither character is particularly responsible or practical, much to the chagrin of Bronstein's Rachel.
"Act like a person," Rachel tells Gen early on. Throughout the film, Rachel lectures Gen, Alice, and pretty much every person they cross paths with on how to act like a person. A person, of course, being someone just like Rachel.
At least one film critic dismissed Yeast as Mary Bronstein's "vanity publishing project"; while he didn't specify, I suspect he saw the film as Poor Mary Bronstein, the Last Normal Person in the World, beset by Freaks and Weirdos. And I can see where someone can misread the film in that fashion: towards the end there is an actual freak show, Rachel gawking at it with the same incomprehension and abject disgust which with she gawked at Gen, Alice, and the rest of the film's characters.
But that is, in the end, a misreading that is not really supported by the film or its structure. A little less than half of the film's fleeting and tight 78 minutes are dedicated to a camping/hiking trip undergone by Rachel and Gen. Through-out that sequence, we are indeed invited to gawk at Gen, so much so that those moments when Rachel pushes or goads her ("so, do you have any friends?") fade into the background. That sequence is capped by an act of violence, at once so mundane and yet so extreme that it is frightening. In that section of the film, we identify strongly with Rachel.
But then the film changes. The focus shifts to Alice. Alice isn't obnoxious like Gen; Alice doesn't steal party hats or sneak into closed sections of fast food restaurants. Alice just wants to be left alone. But Rachel won't let her.
Rachel keeps pushing at her, belittling her ("while you're washing the dishes, you might get an idea to wash yourself"), telling her what to do and when to do it. Rachel is, for lack of a better word, a bully. If this is a film about, as the film's website says, two "toxic relationships", it is really Rachel that is the toxic element. Rachel refuses to let people be themselves. She is the ultimate xenophobe: anyone who is not Rachel like is not acting "like a person". The character is not only self-absorbed, but like certain persons on the autism spectrum lacks any conception of other people.
And this someone calls a vanity project? Frankly, I don't see it. What I see instead is a terrific performance by an actress who is not concerned with something as petty as her character being "likeable". It's a rare skill shared by all three actresses in Yeast.
One could argue that Bronstein's "point" regarding Rachel's inability to leave people alone is diminished because Gen and Alice are themselves such unlikeable characters, Gen being potentially dangerous and Alice being generally unsavory in her personal hygiene. And, yes, you'd be hard-pressed to find an audience member who would express tolerance for a roommate who refused to wash dishes or pick up after themselves.
But Yeast is, in the end, a film and films are not about making points but about providing experiences. Our understanding of Rachel arises gradually and out of the film's structure. The extremes of Gen and Alice prevent us from taking one side or the other, and thus encourage a more nuanced understanding of all three women.
The film's ambiguity and unflinching savagery mark it as an essential experience that I cannot recommend enough. Please, do yourself a favor and let Yeast infect you. Let it hurt you; you'll love it.