Editing Emulsion (section)

===Instability===
Emulsion stability refers to the ability of an emulsion to resist change in its properties over time.<ref name=":0">{{cite book|author=McClements, David Julian |title=Food Emulsions: Principles, Practices, and Techniques, Second Edition|url=https://books.google.com/books?id=wTrzBPbf_WQC&pg=PA269|date=16 December 2004|publisher=[[Taylor & Francis]]|isbn=978-0-8493-2023-1|pages=269–}}</ref><ref>{{cite journal|doi=10.1016/S0268-005X(99)00027-2|title=Influence of copper on the stability of whey protein stabilized emulsions|journal=Food Hydrocolloids |volume=13 |issue=5 |pages=419 |year=1999 |last1=Silvestre |first1=M.P.C. |last2=Decker |first2=E.A.|last3=McClements|first3=D.J.}}</ref> There are four types of instability in emulsions: [[flocculation]], [[Coalescence (physics)|coalescence]], [[creaming (chemistry)|creaming]]/[[sedimentation]], and [[Ostwald ripening]]. Flocculation occurs when there is an attractive force between the droplets, so they form flocs, like bunches of grapes. This process can be desired, if controlled in its extent, to tune physical properties of emulsions such as their flow behaviour.<ref>{{Cite journal|last1=Fuhrmann|first1=Philipp L.|last2=Sala|first2=Guido|last3=Stieger|first3=Markus|last4=Scholten|first4=Elke|date=2019-08-01|title=Clustering of oil droplets in o/w emulsions: Controlling cluster size and interaction strength|journal=Food Research International|volume=122|pages=537–547|doi=10.1016/j.foodres.2019.04.027|pmid=31229109|issn=0963-9969|doi-access=free}}</ref> Coalescence occurs when droplets bump into each other and combine to form a larger droplet, so the average droplet size increases over time. Emulsions can also undergo creaming, where the droplets rise to the top of the emulsion under the influence of [[buoyancy]], or under the influence of the [[centripetal force]] induced when a [[centrifuge]] is used.<ref name=":0" /> Creaming is a common phenomenon in dairy and non-dairy beverages (i.e. milk, coffee milk, [[almond milk]], soy milk) and usually does not change the droplet size.<ref name=":1">{{Cite journal|last1=Loi|first1=Chia Chun|last2=Eyres|first2=Graham T.|last3=Birch|first3=E. John|date=2019|title=Effect of mono- and diglycerides on physical properties and stability of a protein-stabilised oil-in-water emulsion|journal=Journal of Food Engineering|volume=240|pages=56–64|doi=10.1016/j.jfoodeng.2018.07.016|s2cid=106021441|issn=0260-8774}}</ref> Sedimentation is the opposite phenomenon of creaming and normally observed in water-in-oil emulsions.<ref name=":2" /> Sedimentation happens when the dispersed phase is denser than the continuous phase and the gravitational forces pull the denser globules towards the bottom of the emulsion. Similar to creaming, sedimentation follows [[Stokes' law]].

An appropriate surface active agent (or surfactant) can increase the kinetic stability of an emulsion so that the size of the droplets does not change significantly with time. The stability of an emulsion, like a [[Suspension (chemistry)|suspension]], can be studied in terms of [[zeta potential]], which indicates the repulsion between droplets or particles. If the size and dispersion of droplets does not change over time, it is said to be stable.<ref>{{Cite journal|last=Mcclements|first=David Julian|date=2007-09-27|title=Critical Review of Techniques and Methodologies for Characterization of Emulsion Stability|journal=Critical Reviews in Food Science and Nutrition|volume=47|issue=7|pages=611–649|doi=10.1080/10408390701289292|issn=1040-8398|pmid=17943495|s2cid=37152866}}</ref> For example, oil-in-water emulsions containing [[Mono- and diglycerides of fatty acids|mono- and diglycerides]] and milk protein as surfactant showed that stable oil droplet size over 28 days storage at 25&nbsp;°C.<ref name=":1" />