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Hypothesis: The rheology of milk fat, which is strongly related to its functionality, reflects multiscale structural transitions in the colloidal network formed by crystallizing triacylglycerols., Experiments: To relate rheology to structure, early stages of milk fat crystallization at 15-22 °C were studied combining different techniques; XRD and microscopy to study structural changes, NMR to quantify the different structures, and rheology to evaluate their effect on macroscopic properties., Findings: Network strength increased with the synchronized formation of micro- and nanostructures. A rheological response was only obtained when these structures became visibly connected on a microscale, and internal transitional changes could be detected with rheology. On the nanoscale, transitions were linked to the formation of specific crystal polymorphs. We quantified the formation of polymorphs commonly found in milk fat (α-2 and β 1 ' -2) and of two less commonly obtained polymorphs: β-2 and β 2 ' -2. For the first time, the formation of these polymorphs was quantified and related to the composition of fat. Besides providing insights into the complex phase behavior of milk fat, this study shows that the structural transitions involved can be characterized and quantified by combining XRD with NMR and be detected at an early stage using rheology and microscopy., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)