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Lemon Isinglass, or Gelatine, Jelly
Rub the yellow rind of three large fresh lemons upon half a pound of sugar. Pour over it the carefully-strained juice of six lemons, and put it into an enamelled saucepan, with one ounce of isinglass, a pint of water, and a large wine-glass of sherry. Stir these over the fire until the isinglass is dissolved. Strain the jelly through a bag, and if it is not perfectly transparent, mix it, when quite cool, with the whites and crushed shells of three eggs whisked with a quarter of a pint of cold water. Let the jelly boil for three minutes without stirring, then let it settle for five or six minutes, and strain it again. Time, about an hour to prepare. Probable cost, exclusive of the sherry, 3s. Sufficient for a quart of jelly.
A Victorian clear jelly, built on the acid of six lemons and clarified with an egg-white raft. The technique is straightforward; the quantities need translating, and the setting agent is not what modern cooks buy.
- Isinglass to gelatineIsinglass is dried fish swim-bladder collagen, sold in leaf or shred form and no longer a kitchen staple. Substituting powdered gelatine is not a straight swap by weight: period sources disagree on the equivalence. Judged as gelatine alone, one ounce (28 g), about four standard 7 g envelopes, would be firm for a quart of a heavily acidic jelly; 20-25 g gives a mould that unmoulds cleanly without being rubbery.
- Acid and setting strengthSix lemons' juice plus sherry is a lot of acid, and prolonged boiling in acid breaks gelatine down. Dissolve it over gentle heat and take it no further than the three-minute clarifying boil the recipe allows.
- Imperial measuresThe pint here is an imperial pint, 20 fl oz. A "large wine-glass" in Victorian cookery books is about 2 to 2 1/2 fl oz. Half a pound of sugar is 225 g, roughly a generous cup.
- Rubbing the rind on sugarThis is the technique now known as oleo-saccharum: the sugar crystals abrade the zest and draw out the lemon oil. It is an effective way of capturing the aroma of the peel, and worth the few minutes of work.
- Enamelled saucepanNot decorative advice. Bare iron, copper or aluminium react with that much lemon juice and will dull the colour and taste metallic. Use enamel, stainless steel or glass.
- The clarificationThe hinge of the whole thing. Add the whisked whites and shells only when the jelly is cool, or they cook into strings instead of forming a raft. Once it boils, do not stir and do not let it gallop, or the raft breaks up and clouds the jelly again.
- StrainingA jelly bag or a double layer of scalded muslin in a sieve. Wet and wring the cloth first, let it drip, and resist squeezing it, which pushes fine sediment straight through.
- Setting and yieldA quart (an imperial quart is about 1.1 litres), enough for eight small moulds or one large one. Allow four to six hours in the refrigerator, longer for a large mould; the stated hour is preparation time only and excludes setting.
Isinglass reached the Victorian kitchen by way of the fish trade: it is a preparation of the dried swim bladders of sturgeon and related fish, imported chiefly from Russia, and it was valued both as a setting agent and as a fining for beer and wine. A clear jelly was the standard by which a cook's care was judged, and clarity had to be won by technique rather than bought in a packet. The egg-white raft, the jelly bag and the injunction not to stir all belong to that discipline. Commercially refined gelatine, cheaper and made from land-animal collagen, steadily displaced isinglass in domestic use over the later nineteenth century, which may be why the book hedges its title with "or Gelatine" -- though the notion of a recipe caught mid-substitution is conjecture. The sherry is priced separately, though excluding wine and spirits from a costing is a standard convention in these books.