A practical non-destructive method for rejection of unripe 'Elstar' apples

Unripe 'Elstar' apples early in season should be excluded from the market in order to avoid a suboptimal start of the marketing season. The existing control system in the Netherlands, based mainly on a general release date and a starch degradation criterion is functioning unsatisfactorily, especially because early orchards are not credited. Improved systems should recognise early orchards (promoting individual growers' interests) without increasing the risk of unripe fruit entering the market (protecting general growers' concerns). During a period of 4 years, samples from 6 orchards varying in earliness were collected weekly, starting 4 weeks before the expected release date and ending two weeks after, and divided into two parts. One part was kept for 8 days at room temperature (normal marketing scenario) and subsequently used for sensory evaluation (overall acceptability, 1-10 scale). The other part was used for measuring weight, ground colour (a * b * L), firmness, starch degradation stage, total soluble solids (TSS) and acid concentration (TA) at harvest. Multiple regression analysis of characteristics at harvest against taste after 8 days showed that the best possible model based on such criteria was no better or only slightly better than the best possible model based on the non-destructive characteristics of weight and ground colour. Basic data as well as tests in year 5 showed the latter to give right decisions >80% compared to ca. 50% by the old starch-based system. The success appeared to be due entirely to an increase in the number of right approvals. Thus, the new system recognises early' orchards and rewards individual growers much better, without significantly increasing the risk of unripe fruit entering the market. In addition it is faster, non-destructive and more objective. The new system will be used in 1996 with a portable application (colour meter plus laptop).