물성 ≫ 유화 ≫ 거품  

기포 방법

- 발효, 탄산주입
- 강한 교반 : 마쉬멜로
- 강한 비등
- 압력제거등으로 용해도 감소
- 팽창제 사용 : 중조등


Foams are very similar to emulsion where air is the hydrophobic phase instead of oil
Principle of foam formation is similar to that of emulsion formation (most of the same factors are important)
- Foam capacity : determined by volume increase immediately after whipping.
- Foam stability :  the volume of the foam that remain after time. Can be expressed as a percentage of the initial foam volume.


Foams are typically formed by:
- Injecting gas/air into a solution  through small orifices
- Mechanically agitate a protein solution (whipping)
- Gas release in food, e.g. leavened breads (a special case)

거품의 영향요소
Type of protein
- Increased surface hydrophobicity is good
- Partially denaturing the protein often produces better foams
- Globular is better than fibrous

pH
Foam formation and stability is often bad at around pI of the proteins. At the isoelectric point, the total charge of protein molecules is close to zero which leads to their aggregation and coagulation. The higher molecular weight complexes impair the formation of viscoelastic protein film at the boundary of the two phases which is mandatory for stabilization of the foam.

Salt: protein dependent
- Egg albumins, soy proteins, gluten : Increasing salt usually improves foaming since charges are neutralized (they lose solubility  salting-out)
- Whey proteins : Increased salt negatively affects foaming (they get more soluble – salting-in)

Lipids : 지방함량
- Lipids in food foams usually inhibit foaming by adsorbing to the air-water interface and thinning it.
- Only 0.03% egg yolk (which has about 33% lipids) completely inhibits foaming of egg white!
- Cream is an exception where very high level of fat stabilizes foam

Stabilizing ingredients
- Ingredients that increase viscosity of the liquid phase stabilize the foam (sucrose, gums, polyols, etc.)
- add sugar to egg white foams at the later stages of foam formation to stabilize
- Addition of flour (protein, starch and fiber) to foamed egg white to produce angel cake (a very stable cooked foam)

Energy input
- The amount of energy (e.g. speed of whipping) and the time used to foam a protein is very important
- To much energy or too long whipping time can produce a poor foam
- The foam structure breaks down, Proteins become too denatured