This study turns to what is for many an everyday item – yogurt – as a critical zone observatory, a synergistic, place-based laboratory which aims to integrate heterogenous representations of planetary phenomena as they are registered at a common surface. Yogurt has an impressive cultural endurance largely derived from its prominence in various paradigms of health. The product has culturally endured in another sense: as a common cultural medium where humans and microbes have met for generations. This study begins with a profile of yogurt as most encounter it today to consider how normative notions of health interface with the temporal and spatial imaginaries entailed in commodity geographies. Commoditized yogurt is characterized by a low and limited microbial biodiversity compared to yogurts produced outside of the commodity context. Yogurt is therefore presented as a micro case study to consider modes by which we sense and valuate ecological phenomena beyond the perceptible surface, how such sens-abilities intersect models of health, and to what effect. To trace a history of yogurt along these contours, I introduce it as a particular kind of artefact: a global object. As an object of environmental history, I define a global object as a global commodity with a high potential to be re-localized, and therefore with a high potential to re-shape commodity geographies. However, this trajectory is contingent upon framing yogurt as a critical zone observatory – a site where global phenomena like human-microbial interaction may become familiar and intimate. Guided by new materialist theory, I weave together historical and ethnographic case studies from the following consortium: resident yogurt bacteria, artisanal yogurt producers and home fermenters, a mystical immunologist, and an 11th century linguistic scholar. Through these perspectives, I both sketch and apply a framework for de-centered, interspecies histories of cultural (re)production through an extended metaphor of biofilm: the coagulative bacterial structure giving yogurt its characteristic texture. In so doing I provide a re-articulation of “the probiotic” as an integrative case of human and more-than-human health. The study concludes by directing these implications towards a consideration of aesthetic engagement by displaying how fermentation practice may enliven matters of re-diversification and re-localization.