# Commission Regulation (EEC) No 2568/91 of 11 July 1991 on the characteristics of olive oil and olive-residue oil and on the relevant methods of analysis, Division 9.1.2: When organoleptically assessing a virgin olive oil, it is recommended that FOUR SAMPLES at the most be evaluated in each session with a maximum of three sessions per day, to avoid the contrast effect that could be produced by immediately tasting other samples.

Extent: E+W+S+N.I.

As successive tastings produce fatigue or loss of sensitivity caused by the preceding samples, it is necessary to use a product that can eliminate the remains of the oil from the preceding tasting from the mouth.
The use of a small slice of apple is recommended which, after being chewed, can be disposed of in the spittoon. Then rinse out the mouth with a little water at ambient temperature. At least 15 minutes shall lapse between the end of one session and the start of the next.

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Source: https://www.legislation.gov.uk/eur/1991/2568/annex/XII/division/9/division/9.1/division/9.1.2 (the official version)
Page: https://openlegislation.uk/eu-regulation-1991-2568/annex-XII/division-9/division-9.1/division-9.1.2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.