This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
When thoroughly ripened and finely finished, in appearance as a Black Grape it has no equal. When badly matured it is but an indifferent variety. The too frequent defectiveness of this noble variety is entirely obviated by an earlier and longer subjection to a higher temperature than is generally applied to late varieties. Though less in size of berry than the "Duke of Buccleuch," yet individually they are very large. When grown under the customary practice of late starting, or natural starting, as it is often plausibly termed - that is, the withholding of fire-heat until the advance of genial weather promotes growth, little signs of vitality are observable until well into April or even May. By the month of September colouring is not well begun; and however much fire-heat may be employed after that time, they never acquire that degree of perfection gained by those started in March, when colouring commences at a much earlier date, under the influence of that amount of sun-heat indispensable to the complete ripening of Grapes that are intended to remain in a presentable condition during winter. Where the saving of fuel is aimed at, early-ripened Grapes require far less firing while keeping, which more than recompenses for the first outlay.
Fire-heat, on the other hand, fails in preventing shrivelling and decay in the case of badly-ripened crops. My object is to commend Gros Colman as being one of the very few Vines of Continental origin possessing sufficient merits to secure for itself a place, and warrant its extensive cultivation, in our British collections. Gros Colman, next to Lady Downes, is the most worthy of a place in every vinery where late-keeping Grapes are grown. Its handsome compact round bunches, large globular berries, with a peculiarly palatable soft rich flavour, with skins as thin as those of a Hambui'g, and retaining a plump condition of berry for a long time, render it a late Grape of great value.
Previous to this Vine being extensively planted at the Tweed Vineyard, I am not aware that it existed in any quantity in Scotland. I understand its captivating appearance as seen at the Vineyard during last season has created a great demand for it. J. M.