Continental (Dry Gum, or 4:2:1) Method
The continental method is used to prepare the initial or primary emulsion from
oil, water, and a hydrocolloid or "gum" type emulsifier (usually acacia).
The primary emulsion, or emulsion nucleus, is formed from 4 parts oil, 2 parts
water, and 1 part emulsifier. The 4 parts oil and 1 part emulsifier represent
their total amounts for the final emulsion.
In a mortar, the 1 part gum is levigated with the 4 parts oil until the powder
is thoroughly wetted; then the 2 parts water are added all at once, and the
mixture is vigorously and continually triturated until the primary emulsion
formed is creamy white and produces a "crackling" sound as it is triturated
(usually 3-4 minutes).
Additional water or aqueous solutions may be incorporated after the primary
emulsion is formed. Solid substances (e.g., active ingredients, preservatives,
color, flavors) are generally dissolved and added as a solution to the primary
emulsion. Oil soluble substance, in small amounts, may be incorporated directly
into the primary emulsion. Any substance which might reduce the physical stability
of the emulsion, such as alcohol (which may precipitate the gum) should be added
as near to the end of the process as possible to avoid breaking the emulsion.
When all agents have been incorporated, the emulsion should be transferred to
a calibrated vessel, brought to final volume with water, then homogenized or
blended to ensure uniform distribution of ingredients.