layer of oil (as in a vinaigrette) or butter.
Old Tricks for Green Vegetables
Cooks had worked out the practical
chemistry of chlorophyll long before it had
a name. The Roman recipe collection of
Apicius advises, “omne holus smaragdinum
fit, si cum nitro coquatur.” “All green
vegetables will be made emerald colored,
if they are cooked with nitrum.” Nitrum
was a natural soda, and alkaline like our
baking soda. In her English cookbook of
1751, Hannah Glasse directed readers to
“Boil all your Greens in a Copper Sauce-
pan by themselves, with a great Quantity of
Water. Use no iron pans, etc., for they are
not proper; but let them be Copper, Brass,
or Silver.” Cookbooks of the early 19th
century suggest cooking vegetables and
making cucumber pickles with a copper
ha’penny coin thrown in to improve the
color. All of these practices survived in