Over the last years the field of wine economics has seen a surge in the amount of research carried on. Apart from the charm exerted by the item itself, the wine market is ideal to conduct economic research since it is characterized by the presence of thousands of small and medium enterprises, enormous variety of products, abundance of information and consequent huge information asymmetries among producers and buyers. Wine is an experience good because consumers learn only after purchase about the actual quality of the product. As pointed out by Akerlof (1970), this feature can lead to market failures due to the information asymmetry between the producer, who followed each step of the production process (Dubois and Nauges, 2010), and the consumer. In extreme cases this can prevent agents from buying the good. In order to reduce information asymmetries and avoid market failures wine guides have assumed the function of rating agencies (Hay, 2010)4. An extensive literature relying on hedonic price models has shown that the judgment of experts strongly affects the final price of wines (see, among others, Arias-Bolzmann et al., 2003; Lecocq and Visser, 2006; Dubois and Nauges, 2010) since market prices are most often determined before consumers obtain any direct and personal information about the quality of the wine of the current year (Castriota and Delmastro 2011, Landon and Smith, 1997; 1998)5. As shown by Ali et al. (2008), famous gurus like Robert Parker can affect even en-primeur wine prices. Therefore, wine guides represent a key factor that affects the market price mechanism (Oczkowski, 2001). In spite of its prominence in shaping market equilibria, a number of studies have started pointing out that wine experts may differ in their opinion (Cliff and King, 1997; Ashenfelter, 2006; Hodgson, 2008). This paper aims at providing new evidence on wine experts’ behaviour when forming quality ratings. Using a unique database on Italian wines we show that tasters’ quality evaluations are affected by personal bias, which leads judges to be systematically more or less generous than their colleagues, and by personal preferences towards certain wine characteristics. Our results are even more interesting if we think that the tasters under scrutiny here work for the same wine guide and share a set of common and agreed tasting and rating rules.