Yoghurt separation is the release of whey, a protein-rich liquid that is part of milk. This can happen due to:
Syneresis - the technical term for liquid separating from gel, it occurs when the yoghurt's protein network contracts and releases liquid.
Weak gel structure - if yoghurt's protein network is not strong enough it cannot hold in the whey.
Acid development - as lactic acid bacteria ferment lactose, it lowers the pH. If the pH gets too low, the proteins shrinks and expel moisture.
Mechanical stress - Shaking, transporting or even just scooping yoghurt, can break the gel and cause separation.
Storage time & temperature - over time, especially if stored warm, the protein structure can weaken and release whey.
To prevent or reduce separation during yoghurt manufacturing, there are several techniques that can be used:
Use of stabilizers - stabilizers help bind water and stabilise the gel structure to reduce whey separation. Some examples are pectin, gelatine, guar gum or modified starch.
Increase total solids - add milk powders before fermentation, the higher the solids the stronger is the protein network, resulting in less syneresis.
Optimize heat treatment - pasteurization is crucial before fermentation, this heat treatment ensures that the proteins are denatured and helps them binding with casein, improving gel strength.
Control incubation conditions - incubate at the optimum temperature required for the specific starter culture [take into account long set or short set incubation] until a pH of 4.6 is reached - don't let the pH go down too far in order to avoid over-acidification and gel shrinkage.
Minimize post-fermentation agitation - set-styled yoghurt is fermented in the final container, reducing stress. Stirred yoghurt should be handled gently after fermentation to avoid breaking down the gel & body.
Homogenize milk - homogenizing milk improves texture and consistency, contributing to a more stable product.