Russet is the term given to the dull brown and rough finish on the skin of some apples. Some varieties are entirely russeted, and these may or may not be called ‘russets’ – well-known varieties are the mid-season ‘Egremont Russet’ and the earlier ‘St Edmund’s Pippin’. Other varieties are typically partly russeted, particularly around the eye and cavity, and such russet tends to be relatively extensive on late varieties. Some varieties are typically largely free of russet but have a russeted clone, such as ‘Golden Delicious Russet’ (called ‘Bertanne’ in France). Russet can also occur on the apples of any variety following injury or other malformation during the growth of the fruit.
The English are generally tolerant or approving of russet. The roughness of the skin is not thought to detract from eating quality, and partial russet is often regarded as visually pleasing, offsetting the brighter cheeks of the fruit. Russet also has traditional connotations: English varieties tend to be less brightly coloured than those grown overseas, and many of those most highly esteemed for eating quality have quite muted colouring, with appreciable russet.
The association that springs to mind, of russet with flavour, is the distinctive flavour of Egremont Russet, sometimes called ‘sere russet’, which is conferred by a particular composition of aromatics. In fact this association is a coincidence since other russets do not possess this flavour, while some non-russets do (giving a related aniseed or fennel flavour to ‘Ellison’s Orange’ or ‘Merton Beauty’, for example).
However, russet does seem to have an association with flavour. Hall (1933), then Director of the John Innes Horticultural Institution, wrote that there seems to be some correlation between russeting and the special aromatic flavour of the English type of dessert apple. Of five varieties with a russeted form listed by Morgan and Richards (1993), flavour is said to be better in ‘Norfolk Royal Russet’ than in ‘Norfolk Royal’, more interesting in ‘Golden Delicious Russet’ than in ‘Golden Delicious’, and bold (with a sere russet character) in ‘King Russet’ compared to ‘King of the Pippins’. On the other hand, in the other two, ‘Russet Lambourne’ is said to have the same flavour as ‘Lord Lambourne’, while no comment is offered on the flavour of ‘Laxton’s Russet Superb’ compared to ‘Laxton’s Superb’.
In a more formal study, ‘Golden Delicious Russet’ was slightly sweeter and had a stronger aroma than ‘Golden Delicious’, and the greater the russeting in different clones of ‘Golden Delicious’ the greater the weight loss after four months in cold storage (Sansavini and Bassi, 1977). Thus, in this study, russeted skin was relatively permeable to water, suggesting a mechanism by which russets develop a different flavour from their unrusseted forms.
As the apple develops on the tree, water loss from the apple tends to increase the inflow of sap, increasing the content of ions and metabolites. These could increase the dry matter of the apple or increase the intensity of flavour, or both, although it is difficult to see how the flavour could become very different in russet forms. It should be noted that water can also be exported from the fruit to other parts of the tree in times of water stress in the whole plant (Tromp, 1984), and conceivably ions or metabolites could be carried away from the fruit in this reverse flow. However, such flow would be expected to affect the fruit of russet and non-russet varieties more or less equally.
The speculation predicts that a thick and impervious skin should be associated with weak flavour, as is seen in fact in ‘Idared’ and ‘Baldwin’, for example, and that varieties noted for intensity of flavour should have relatively permeable skin, whether or not they are russeted. Of these, for example, ‘Ribston Pippin’ has a tendency to shrivel when over-ripe (Bunyard, 1916), and ‘Orleans Reinette’ has a tendency to shrivel in store (Hessayon, 1995).
In conclusion, the russeted skin of apple appears to be relatively permeable to water. This may increase the intensity of flavour (or dry matter content) by increasing the rate of water loss from the fruit while it is growing, hence the rate of inflow (through the stalk), which is expected to bring with it metabolites and flavour compounds.
Author: Wilson, P.J. 2006. The association of russet with flavour in apples. Newsletter of the Royal Horticultural Society Fruit Group 30: 6-7. February 2006. Published with the permission of the author and the RHS.
Bunyard, E.A. 1916. The history of the classification of apples. Journal of the Royal Horticultural Society XLI (III): 445-464.
Hall, A.D. 1933. Preface to The Apple, Crane, M.B. and Hall, A.D.
Hessayon, D.G. 1995. The Fruit Expert. Transworld Publishers Ltd., London.
Morgan, J. and Richards, A. 1993. The Book of Apples. The Ebury Press, London.
Sansavini, S. and Bassi, D. 1977. Clonal selection, fertility and fruit quality of ‘Golden Delicious. In: Symposium on clonal variation in apple and pear. Acta Horticulturae 75: 73-85.
Tromp, J. 1984. Diurnal fruit shrinkage in apple as affected by leaf water potential and vapour pressure deficit of the air. Scientia. Horticulturae. 22: 81-87.