The idea of using wood ash lye held merit and I felt that I needed to spend some time researching the use of lye, or rather, potash in cooking. Using potash in cooking has its roots in Mesoamerican cooking. The Aztecs and Mayans used potash and slaked lime to break down the outer layer and endosperm of ancient corn to soften it and make it edible. This had the added benefit of increasing the nutritional content of food prepared this way.
Prior to the invention of baking soda in the 1800's, leavening was done through the use of yeast. Native Americans can be credited with the discovery of the first chemical leavening agents. According to Michel Suas in his "Advanced Bread and Pastry" book "In 1750, the first chemical leavening agent was used. Known as pearl ash (potassium carbonate), it was created from natural ash of wood and other natural resources. Before potash was available, cake textures were dense. Ammonia was used also as a leavening agent. A solution of water and ammonia was made and a drop of that solution was inserted on top of the cake batter. The center of the cake would rise as in Madeleine's. Yeast was also commercially produced from the late 1800s, and was relied upon more and more over perpetuated natural starters. Additional chemical leavening agents (potassium bicarbonate and sodium bicarbonate) were created by the turn of the 19th century, but it wasn't until the 1850s that these inventions were widely accepted and used regularly (Meyer, 1998, p. 10)."
What makes wood ash so special? Wood ash contains alkaline salts, which create a chemical reaction when mixed with something acidic. This reaction lightens and raises batter by creating gas pockets.
Yeast is an example of a leavening agent. It converts carbohydrates into alcohol creating carbon dioxide. It was not commercially available until the 1800's. Prior to the 1800's the use of yeast as a leavening agent was dependent upon wild yeasts. Platina reminds us that leaven needed to be introduced to flour, water and salt to create bread.
Original recipe from Platina pp. 13-14 (Book 1):
"... Therefore I recommend to anyone who is a baker that he use flour from wheat meal, well ground and then passed through a fine seive to sift it; then put it in a bread pan with warm water, to which has been added salt, after the manner of the people of Ferrari in Italy. After adding the right amount of leaven, keep it in a damp place if you can and let it rise.... The bread should be well baked in an oven, and not on the same day; bread from fresh flour is most nourishing of all, and should be baked slowly."Pot Ash (potash) and Lye originate from wood ashes. This is because wood ash contains both potassium hydroxide (lye) and potassium carbonate (potash, pearl ash, saleratus). The production of lye is the first step in producing potash. The following set of instructions for making lye can be found in "A Treatise on Domestic Economy For the Use of Young Ladies at Home and at School, 1845".
To make Ley. Provide a large tub, made of pine or ash, and set it on a form, so high, that a tub can stand under it. Make a hole, an inch in diameter, near the bottom, on one side. Lay bricks, inside, about this hole, and straw over them. To every seven bushels of ashes, add two gallons of unslacked lime, and throw in the ashes and lime in alternate layers. While putting in the ashes and lime, pour on boiling water, using three or four pailfuls. After this, add a pailful of cold soft water, once an hour, till all the ashes appear to be well soaked. Catch the drippings, in a tub, and try its strength with an egg. If the egg rise so as to show a circle as large as a ten cent piece, the strength is right; if it rise higher, the ley must be weakened by water; if not so high, the ashes are not good, and the whole process must be repeated, putting in fresh ashes, and running the weak ley through the new ashes, with some additional water. Quick-ley is made by pouring one gallon of boiling soft water on three quarts of ashes, and straining it. Oak ashes are best.Slaked Lime (Calcium Hydroxide) was added to the ashes in order to increase the strength of the lye.
Once the lye was drained off, the sludge left behind could then be boiled down to make potassium rich potash also known as black salt. To refine, it was then heated in a kiln to burn off impurities and create a white salt which was commonly known as pearl-ash which could be used in cooking along with something acidic to create carbon dioxide bubbles and lighten baked goods.
Want to make your own ash water to cook with? The method is quite simple--boil a half cup of clean ash with 2 cups of water. Once it has come to a boil, remove the mixture from the heat and allow it to settle. Pour off the clean liquid and strain it. Use this water as your leaven.
To answer the original question--could "fyne leyes" refer to fine lye? No, it was not used in period as a leavening agent.
For more information on cooking with wood ashes and ash water visit the following link: 5 Acres and a Dream
An Experiment with Period and Non-Period Leaveners
Cook's Thesaurus: Leavens
First Night Design | Melomakarona (Μελομακάρονα) Traditional Greek Treat