Because of the interaction of calcium and milk proteins during heating, the effects of enhanced and reduced levels ofcalcium on the physical properties of acid-induced gels such as yoghurt have been investigated. The effects of theremoval of Ca2+are complex and depend on both the method and extent of removal. Remo val by TSC resulted in an increase in the gel strength (as given by G0) of set yoghurt gels up to 20 mM TSC addition but a decrease ingel strength with higher additions (Ozcan-Yilsay et al.2007). However, addition of TSC up to 4 mM caused aslight increase in the firmness (as measured by a textureanalyser) and viscosity of a stirred yoghurt, but addition of up to 16 mM decreased firmness and viscosity (Ramasubra-manian et al. 2008). A similar trend, but with greater effect,was observed when calcium was removed by ion exchange;the gel firmness and viscosity increased considerably up to~5.6 mM calcium removal, but decreased with furtherremoval. Interestingly, the graininess o f the yoghurt, whichwas measured by the number of nodules in a certain volume, incre ased markedly when >~5.6 mM calcium wasremoved (Ramasubramanian et al. 2008).Addition of Ca2+(as calcium chloride) to stirred yoghurtincreased gel firmness and viscosity up to ~2 mM additionand decreased these properties with further addition to themaximum added, 13.6 mM. The graininess of the yoghurtincreased with increasing calci um chlor ide addition from 0to the maximum added. Curiously, a soluble nonion ic formof calcium, calcium potassium citrate (Gadocal Kâ; GadotBiochemical Industries Ltd), behaved quite different ly fromionised calcium salts when incorporat ed into stirred yoghurt.The gel firmness and viscosity of the yoghurt showed con-siderable increases with additions up to 50 mM, and these increases were generally accompanied by decreas ed graini-ness