Green Colouring Butter

Ingredients

Equipment Needed

• •Salad spinner and clean kitchen towels
• •Food processor
• •Strong lint-free flour-sack towel
• •Heatproof bowl and saucepan for the bain-marie
• •Fine-mesh sieve and tightly woven cloth
• •Digital kitchen scale accurate to 1 g
• •Small mortar and pestle or sturdy bowl and spatula
• •Palette knife or small offset spatula

Instructions

1. 1

   Pick and dry

   Pick over the spinach, removing coarse stalks and any damaged leaves. Wash it thoroughly in two changes of cold water, lift it out so grit stays behind, then spin and spread it on clean towels until every trace of washing water is gone. External water dilutes the juice and lengthens the coagulation, so be severe about the drying.

2. 2

   Pound and press

   Process the raw spinach in batches, scraping down often, until it becomes a wet, finely pounded paste. Add no water. If the blades cannot catch the leaves, chop them roughly first and return them to the processor. Scrape the paste into the centre of a strong, lint-free cotton towel, gather the corners, and twist firmly over a bowl until the stream slows to reluctant drops. The juice is what you need; reserve the squeezed pulp for soup or discard it.

3. 3

   Coagulate the juice

   Pour the raw juice into a heatproof bowl and set it over a saucepan of barely simmering water, keeping the bowl above the water itself. Warm it gently for 8 to 15 minutes. Deep green flecks will gather while the surrounding liquid becomes thinner and duller. If nothing separates after eight minutes, raise the bath to a quiet simmer and continue. Ça se rattrape. If the spinach juice itself begins bubbling, lift the bowl away at once, lower the heat, and resume more gently.

   Do not whisk the juice. One or two slow turns with a spoon are enough to distribute the heat without breaking the delicate green coagulum into particles that escape through the cloth.
4. 4

   Drain the colour

   Line a fine-mesh sieve with a dampened, tightly woven lint-free cloth and suspend it over a bowl. Pour in the contents of the bain-marie and leave them to drain for 15 to 20 minutes. Fold the cloth over and press gently to remove free water, then collect every scrap of deep green colouring matter with a palette knife. If green flecks passed through, line the sieve with a coffee filter and strain the collected liquid again.

5. 5

   Work in butter

   Weigh the drained colouring matter, then weigh softened unsalted butter equal to exactly half that amount. For example, 28 g of colouring matter takes 14 g of butter. Pound them together in a small mortar or work them firmly with a spatula until no pale butter streaks remain, then press the mixture through a dry fine-mesh sieve and scrape it from the underside. If the butter melts and the mixture turns oily, stop and chill it for 5 to 10 minutes until opaque but pliable, then work it again. The finished beurre colorant vert should be smooth, dense, and intensely green.

   The half-weight ratio is not an estimate. Too much butter weakens the tint; too little leaves a damp vegetable paste that keeps poorly.
6. 6

   Portion and chill

   Pack the beurre colorant vert into a small covered jar, or spread it between parchment into a thin slab and score it into tiny portions. Chill until firm. To colour a finished sauce, take the sauce off the heat and whisk in a small piece at a time, beginning with about 1/8 teaspoon per cup. Stop when the colour is fresh and clear. Do not boil the sauce afterward, or the green will dull. À table!

Chef Tips

• •Choose mature, dark spinach with crisp leaves. Baby spinach works, but its paler leaves usually give less colouring matter and a weaker finished butter; frozen spinach cannot supply the necessary raw juice.
• •Expect the yield to vary with the spinach. Trust the scale, not an assumed spoon measure: whatever the drained green matter weighs, use half that weight in butter.
• •Add beurre colorant vert only after a sauce has finished reducing. Reduction after colouring concentrates the spinach taste and prolonged heat turns the green drab.
• •This preparation carries no salt because it must enter sauces that are already seasoned. Butter, not margarine. A fat substitute weakens both its texture and its keeping quality.
• •Commercial liquid colouring reproduces the hue without the quiet, natural character of spinach. The whole purpose of this formula is to make the bottle unnecessary.

Advance Preparation

• •Make the beurre colorant vert up to 5 days ahead and keep it tightly covered in the refrigerator. Press parchment directly against its surface to limit oxidation.
• •For longer keeping, freeze the butter in tiny scored portions for up to 3 months. Break off only what the sauce needs and whisk it in directly from frozen, off the heat.
• •The spinach may be washed and dried a day ahead. Wrap it loosely in a dry towel and refrigerate it, but do not pound or press it until you are ready to complete the preparation.

Frequently Asked Questions

Nutrition Information

1 serving (about 14g)