NOVELTY - Producing an alkyl ester, comprises: transesterification of a first charge having a triglyceride-containing first fat, a first alcohol and a first base to give a first product; contacting the product with a triglyceride-containing second fat to give an intermediate and separating into a first alkyl ester-rich fraction and a first glycerol-rich fraction; contacting the alkyl ester-rich fraction with a second alcohol and a second base and performing transesterification to give a second product and separating into a second alkyl ester-rich fraction and a second glycerol-rich fraction.    USE - The process is useful for producing alkyl esters, preferably methyl ester from triglyceride-containing fats such as vegetable and animal fats (claimed) to form biofuels e.g. biodiesel.    ADVANTAGE - The process provides high quality methyl ester from low grade feedstock. The process reduces the cost for removing, purifying, and/or recycling excess methanol from the transesterification reactions, hence is more efficient and cost-effective. The addition of the second charge generates fresh glycerol, which removes e.g. soap, and/or other contaminants from the methyl ester/triglyceride-containing layer to reduce the contaminants that attract glycerol, hence the concentrations of glycerol in the final product can be reduced and effectiveness of the catalyst and/or the purity of the final product can be improved. The process reduces the processing time and the amount of catalyst for transesterifying.    DETAILED DESCRIPTION - Producing an alkyl ester, comprises: introducing a first charge into a reactor, where the first charge includes a triglyceride-containing first fat, a first alcohol, and a first base; performing a first transesterification reaction in which the first fat reacts with the first alcohol to produce a first reaction product that comprises an alkyl ester and glycerol; contacting the first reaction product with a triglyceride-containing second fat to yield an intermediate product; separating the intermediate product into a first alkyl ester-rich fraction and a first glycerol-rich fraction; contacting the alkyl ester-rich fraction with a second alcohol and a second base and performing a second transesterification reaction that produces a second reaction product that comprises glycerol and an alkyl ester; separating the second reaction product into a second alkyl ester-rich fraction and a second glycerol-rich fraction. An INDEPENDENT CLAIM is included for a system for producing an alkyl ester, comprising: a reactor; a feed storage configured to hold at least one triglyceride-containing fat; an alcohol storage configured to hold an alcohol; a catalyst storage configured to hold a catalyst; and a controller operatively coupled to the reactor, the feed storage, the alcohol storage, and a catalyst storage, where the controller has a computer readable medium containing instructions to perform the process.    DESCRIPTION OF DRAWING(S) - The figure shows a flow chart ,illustrating a second transesterification processing stage.    Second processing stage (208)    Adding second fat (220)    Mixing and settling second and first fat (222)    Decanting first glycerol (224)    Adding methanol and/or catalyst. (225)