A variant ester synthase polypeptide comprising SEQ ID NO: 2, wherein said variant ester synthase polypeptide is genetically engineered to have (a) a mutation at amino acid position 15 of SEQ ID NO: 2, or (b) the mutation S15G in SEQ ID NO: 2, or (c) the mutation S15G and mutations T5P, P111S, V171R, P188R, F317W, S353T, V409L and S442G in SEQ ID NO: 2, or (d) the mutation S15G and mutations T5P, K78F, P111S, V171R, P188R, S192V, A243R, F317W, K349H, S353T, V409L and S442G in SEQ ID NO: 2, or (e) the mutation S15G and mutations T5P, V76L, P111S, V171R, P188R, K258R, S316G, F317W, S353T, M360R, Y409L and S442G in SEQ ID NO: 2, or (f) the mutation S15G and mutations T5P, P111S, V171R, P188R, Q244G, S267G, G310V, F317W, A320C, S353T, Y366W, V409L and S442G in SEQ ID NO: 2, or (g) the mutation S15G and mutations P111S, V155G, P166S, V171R, P188R, F317W, Q348A, S353T, V381F, V409L and S442G in SEQ ID NO: 2, or (h) the mutation S15G and mutations L39S, D77A, P111S, V171R, P188R, T313S, F317W, Q348A, S353T, V381F, V409L, I420V and S442G in SEQ ID NO: 2, or (i) the mutation S15G and mutations of T5P, T24W, T44F, P111S, I146L, V171R, P188R, D307N, F317W, S353T, V409L and S442G in SEQ ID NO: 2, or (j) the mutation S15G and mutations T5P, K78F, P111S, V171R, P188R, S192V, R207A, A243R, D255E, L257I, N259Q, L260V, H262Q, G265N, A285V, N288D, N289G, F317W, Q348R, S353T, V381F, V409L and S442G in SEQ ID NO: 2, or (k) the mutation S15G and mutations T5P, K78F, P111S, V171R, P188R, S192V, R207A, A243R, D255E, L257I, N259Q, L260V, H262Q, G265N, A285V, N288D, N289G, F317W, H349K, S353T, V381F, V409L and S442G in SEQ ID NO: 2, or (l) the mutation S15G and mutations T5P, G33D, T44K, Y58L, P111S, R162E, V171R, P188R, R207A, V234C, Q244G, D255E, S267G, D307N, G310V, F317W, A320C, S353T, Y366W, G394E, V409L, S442G and I461V in SEQ ID NO: 2, or (m) the mutation S15G and mutations T5P, G33D, T44K, Y58C, P111S, V171R, P188R, R207A, V234C, Q244G, L257I, S267G, D307N, G310V, F317W, A320C, S353T, Y366W, G394E, V409L, A413T, S442G and I461V in SEQ ID NO: 2, or (n) the mutation S15G and mutations T5P, T44A, P111S, T157S, N164D, T170S, V171R, P188R, R207A, V216I, V234C, Q244G, L257I, S267G, D307N, G310V, F317W, A320C, Q334K, S353T, Y366W, G394E, V409L, S442G and I461V in SEQ ID NO: 2, or (o) the mutation S15G and mutations T5P, Y58L, P111S, R162E, T170S, V171R, A179S, P188R, R207A, V234C, Q244G, L257I, S267G, D307N, G310V, F317W, A320C, S353K, Y366W, G394E, V409L, S442G and I461V in SEQ ID NO: 2, wherein said variant ester synthase polypeptide has improved fatty acid methyl ester activity compared to a corresponding wild type polypeptide. (a) a mutation at amino acid position 15 of SEQ ID NO: 2, or (b) the mutation S15G in SEQ ID NO: 2, or (c) the mutation S15G and mutations T5P, P111S, V171R, P188R, F317W, S353T, V409L and S442G in SEQ ID NO: 2, or (d) the mutation S15G and mutations T5P, K78F, P111S, V171R, P188R, S192V, A243R, F317W, K349H, S353T, V409L and S442G in SEQ ID NO: 2, or (e) the mutation S15G and mutations T5P, V76L, P111S, V171R, P188R, K258R, S316G, F317W, S353T, M360R, Y409L and S442G in SEQ ID NO: 2, or (f) the mutation S15G and mutations T5P, P111S, V171R, P188R, Q244G, S267G, G310V, F317W, A320C, S353T, Y366W, V409L and S442G in SEQ ID NO: 2, or (g) the mutation S15G and mutations P111S, V155G, P166S, V171R, P188R, F317W, Q348A, S353T, V381F, V409L and S442G in SEQ ID NO: 2, or (h) the mutation S15G and mutations L39S, D77A, P111S, V171R, P188R, T313S, F317W, Q348A, S353T, V381F, V409L, I420V and S442G in SEQ ID NO: 2, or (i) the mutation S15G and mutations of T5P, T24W, T44F, P111S, I146L, V171R, P188R, D307N, F317W, S353T, V409L and S442G in SEQ ID NO: 2, or (j) the mutation S15G and mutations T5P, K78F, P111S, V171R, P188R, S192V, R207A, A243R, D255E, L257I, N259Q, L260V, H262Q, G265N, A285V, N288D, N289G, F317W, Q348R, S353T, V381F, V409L and S442G in SEQ ID NO: 2, or (k) the mutation S15G and mutations T5P, K78F, P111S, V171R, P188R, S192V, R207A, A243R, D255E, L257I, N259Q, L260V, H262Q, G265N, A285V, N288D, N289G, F317W, H349K, S353T, V381F, V409L and S442G in SEQ ID NO: 2, or (l) the mutation S15G and mutations T5P, G33D, T44K, Y58L, P111S, R162E, V171R, P188R, R207A, V234C, Q244G, D255E, S267G, D307N, G310V, F317W, A320C, S353T, Y366W, G394E, V409L, S442G and I461V in SEQ ID NO: 2, or (m) the mutation S15G and mutations T5P, G33D, T44K, Y58C, P111S, V171R, P188R, R207A, V234C, Q244G, L257I, S267G, D307N, G310V, F317W, A320C, S353T, Y366W, G394E, V409L, A413T, S442G and I461V in SEQ ID NO: 2, or (n) the mutation S15G and mutations T5P, T44A, P111S, T157S, N164D, T170S, V171R, P188R, R207A, V216I, V234C, Q244G, L257I, S267G, D307N, G310V, F317W, A320C, Q334K, S353T, Y366W, G394E, V409L, S442G and I461V in SEQ ID NO: 2, or (o) the mutation S15G and mutations T5P, Y58L, P111S, R162E, T170S, V171R, A179S, P188R, R207A, V234C, Q244G, L257I, S267G, D307N, G310V, F317W, A320C, S353K, Y366W, G394E, V409L, S442G and I461V in SEQ ID NO: 2,