Mass spectrometry constitutes one of the most encompassing instrumental techniques in science, widely applied in the fi elds of chemistry, biology, medical science and technology. Direct insertion electrospray ionization mass spectrometry (ESI-MS) is a fast and sensitive method which differentiates diverse types of beer, in both positive and negative ion modes, characterizing their main constituents. Although the basic ingredients of beer (water, malt, hops and yeast) have not changed much since the dark ages, variations in these ingredients and in the manufacturing process result in diverse types of beer. The spectra or fi ngerprints of each type of beer permit not only the separation of samples according to their main characteristics, but also further information through the ESI-MS/MS fragmentation of the diagnostic ions of each type, adding another dimension to the analytical results. Fast and characteristic beer fi ngerprint mass spectra were obtained by ESI-MS in both the negative and positive modes. A total of 29 samples of ale produced in Brazil and other countries were divided into three groups by visual analysis of the positive [ESI(+)-MS] and negative [ESI(-)-MS] mode fi ngerprints as well as by chemometric analysis of the data. Many of the marker ions in both modes were found to be simple sugars and oligosaccharides, although their intensities varied depending on the type of ale (pale colored, dark colored and sweetened). This shows that direct infusion ESI-MS could distinguish between samples of ale with different compositions and is promising as a fast and effi cient method of beer characterization. © 2009 Elsevier Inc. 923934Alcázar, A., Pablos, F., Martín, M.J., González, A.G., (2002) Talanta, 57, pp. 45-52Annesley, T.M., (2003) Clin. Chem., 49, pp. 1041-1044Araújo, A.S., Rocha, L.L.R., Tomazela, D.M., Sawaya, A.C.H.F., Almeida, R.R., Catharino, R.R., Eberlin, M.N., (2005) Analyst, 130, pp. 884-889Berlitz, H.D., Grosch, W., Schieberle, P., (2004) F ood Chemistry, , (3rd edn). Springer-Verlag, GermanyCatharino, R.R., Sawaya, A.C.H.F., Cunha, I.B.S., Fogaça, A.O., Facco, E.M.P., Godoy, H.T., Daudt, C.E., Eberlin, M.N., (2006) J. Mass Spectrom., 41, pp. 185-190Cole, R.B., (1997) Electrospray Ionization Mass Spectrometry, , John Wiley & Sons Inc., New YorkCole, R.B., (2000) J. Mass Spectrom., 35, pp. 763-772Cooks, R.G., Zhang, D.X., Koch, K.J., Gozzo, F.C., Eberlin, M.N., (2001) Anal. Chem., 73, pp. 3646-3655Degelmann, P., Becker, M., Herderich, M., Humpf, H.U., (1999) Chromatographia, 49, pp. 543-546Eberlin, M.N., Meurer, E., Santos, L.S., Pilli, R.A., (2003) Org. Lett., 5, pp. 1391-1394Gaumet, J.J., Strouse, G., (2000) J. Am. Soc. Mass Spectrom., 11, pp. 338-344Hans, X.L., Gross, R.W., (2001) A nalytic. Biochem., 265, pp. 88-100Hardwick, W.A., (1995) Handbook of Brewing, , Marcel Dekker, New YorkHofte, A.J.P., van der Hoeven, R.A.M., Fung, S.Y., Verpoorte, R., Tjaden, U.R., Van der Greef, J., (1998) J. Am. Soc. Brew. Chem., 56, pp. 118-122Klampfl, C.W., Himmelsbach, M., Buchberger, W., Klein, H., (2002) Anal. Chim. Acta, 454, pp. 185-191Koch, K.J., Gozzo, F.C., Nanita, S.C., Takats, Z., Eberlin, M.N., Cooks, R.G., (2002) Angew. Chem. Int. Ed. Engl., 41, p. 1721Kotiaho, T., Eberlin, M.N., Vainiotalo, P., Kostiainen, R., (2000) J. Am. Soc. Mass Spectrom., 11, pp. 526-535Mauri, P., Minoggio, M., Simonetti, P., Gardana, C., Pietta, P., (2002) Rapid Commun. Mass Spectrom., 16, pp. 743-748Möller, J.K., Catharino, R.R., Eberlin, M.N., (2005) Analyst, 130, pp. 890-897de la Mora, J.F., Berkel, G.J.V., Enke, C.G., Cole, R.B., Sanchez, M.M., Fenn, J.B., (2000) J. Mass Spectrom., 35, pp. 939-952Raftery, M.J., Geczy, C.L.J., (2002) J. Am. Soc Mass Spectrom., 13, pp. 709-718Rioli, V., Gozzo, F.C., Shida, C.S., Krieger, J.E., Heimann, A.S., Linardi, A., Almeida, P.C., Ferro, E.S., (2003) J. Biol. Chem., 278, pp. 8547-8555Russel, D.H., (1994) Experimental Mass Spectrometry, , Plenum Press, New YorkSawaya, A.C.H.F., Tomazela, D.M., Cunha, I.B.S., Bankova, V.S., Marcucci, M.C., Custódio, A.R., Eberlin, M.N., (2004) Analyst, 129, pp. 739-744Schoonjans, V., Taylor, N., Hudson, B.D., Massart, D.L., (2002) J. Pharm. Biomed. Anal., 28, pp. 537-548Siuzdak, G., (2005) An Introduction to Mass Spectrometry Ionization: An Excerpt from the Expanding Role of Mass Spectrometry in Biotechnology, , 2nd edn. MCC Press, San Diego, CAWhittle, N., Eldridge, H., Bartley, J., Organ, G., (1999) J. Inst. Brew., 105, pp. 89-99Williams, J.D., Flanagan, M., Lopez, L., Fischer, S., Miller, L.A.D., (2003) J. Chromatogr. A., 1020, pp. 11-26Zhang, X.R., Minear, R.A., Guo, Y.B., Hwang, C.J., Barret, S.E., Ikeda, K., Shimizu, Y., Matsui, S., (2004) W ater Res., 38, pp. 3920-3930