Transport by the milk of calcium hydrogen phosphate for biomineralization in next-generation mammals depends on intrinsically disordered casein proteins. Association of calcium to caseins is a two-step process with an initial fast bimolecular reaction with little temperature dependence followed by slower temperature-dependent rearrangements. Dissociation of calcium from caseins appears with negative energies of activation. Dissociation of calcium from caseins seems accordingly to go through different transition states and intermediates than association. Milk hydrogencitrate dissolves colloidal calcium phosphates spontaneously creating strong calcium citrate supersaturation. The degree of local supersaturation increases with decreasing temperature and can like the negative energy of activation seen for dissociation of calcium ions from casein micelles not be accommodated within traditional transition state theory. There is a need for rethinking the dynamics of the reversible calcium association to and dissociation from the caseins in calcium transport going beyond traditional transition state theory to develop novel dairy and non-dairy foods with increased calcium bioavailability.