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Pistachio Paste
Blanch, drain and put into a mortar one pound of pistachios, pound them to a pulp, adding a little orange-flower water to prevent oiling, after which rub them through a fine hair sieve onto a plate. Put one ounce of gum tragacanth previously well soaked and squeeze through a cloth on a marble slab and work it with the hand until it is of a white and elastic appearance, when it may be mixed in with the pistachio pulp and half a pound of finely-sifted icing sugar, beating thoroughly all the while and adding more of the sugar until the paste becomes quite firm, compact and elastic.
This is a confectioner's modelling paste rather than something to eat by the spoonful — the pistachio equivalent of almond marzipan, stiffened with gum so it holds a shape. The hinge is the orange-flower water: pistachios are oily, and without a few drops of liquid to keep the mass moist the pounding turns it into a greasy butter that will never take sugar.
- BlanchingPour boiling water over the shelled nuts, let them stand a minute or two, then drain and slip off the skins. The skins are what dull the colour; removing them is the whole reason for this step, and the paste comes out a much brighter green for it.
- Mortar or machineA food processor does the pounding, but pulse rather than run it — continuous grinding heats the nuts and drives out oil. Add the orange-flower water a few drops at a time as you go; the recipe calls only for 'a little', added during the pounding to prevent oiling.
- Orange-flower waterSold with baking supplies or in Middle Eastern groceries. Use it sparingly; the recipe specifies only 'a little', and a teaspoon or two per pound of nuts should be enough to keep the paste from oiling — much more will dominate the flavour.
- Gum tragacanthStill available from cake-decorating suppliers, sometimes as "gum tragacanth" or E413. An ounce is roughly three to four tablespoons of the modern powder, though in this period it was usually sold as flakes or ribbons; soak it in cold water for several hours until it swells to a stiff mucilage, then squeeze it through muslin as directed to remove lumps and grit. Tylose or CMC powder is the modern substitute in gum pastes.
- The marble slabMarble is used because it stays cool and is non-porous, so it does not take up the oil. A chilled stone or granite worktop works the same way; a wooden board is more absorbent and does not stay as cool.
- Fine hair sieveA drum sieve of horsehair was the standard tool for smoothing pastes. A fine-mesh stainless drum sieve or a sturdy tamis serves, and if the pulp is truly smooth from the processor you can skip the sieving.
- Icing sugarThis is confectioners' or powdered sugar; the modern kind usually contains a little cornstarch as an anti-caking agent, which the sugar of the original would not have had. Sift it; "finely-sifted" is not optional, because lumps show in a paste this pale.
- Yield and useA pound of nuts with half a pound or more of sugar gives roughly two pounds of paste — enough for a great deal of work. It is meant for rolling thin as a covering, moulding into fruits and flowers, or as a green layer in petits fours. Wrapped airtight it keeps for weeks; it dries hard on exposure to air, which is the point of the gum.
Gum pastes of this kind belong to the nineteenth-century pastry chef's repertoire of modelling materials, alongside marzipan, pastillage and nougat, and they were the means by which the elaborate architectural centrepieces of formal banquets were built. Pistachio was prized less for flavour than for colour: before synthetic food dyes were in general use, a green sugar paste often meant pistachios or spinach juice, and the pistachio version was said to be the expensive one. Oscar Tschirky was maître d'hôtel of the Waldorf through the 1890s and after, when a hotel of that rank kept a garde-manger and a pâtissier turning out set pieces for banquet tables, and gum tragacanth — from Astragales shrubs in Persia and Asia Minor, long imported for pharmacy and textile sizing — was the standard stiffener. It survives in the same role today in the gum paste of wedding-cake decorators.