Before baking powder: the ashes that once rose breads, rendered from hearth to hearth, potash and pearlash.

Potash Leavening — Historical Baking with Ashes (Before Baking Powder)

Update (August 27, 2025): Expanded with historical timeline, safety notes, modern substitutions, and FAQ. Cross-linked to our measurement guides.

What did bakers use before baking powder?

Long before handy tins of baking powder, cooks relied on alkalis from wood ash—known as potash and its refined form pearlash—to aerate quick breads, gingerbreads, and biscuits. When combined with an acid (vinegar, sour milk, molasses), potash releases bubbles that lighten doughs. It’s clever chemistry with humble origins.

What Are Potash & Pearlash?

Potash is a broad term for potassium salts from wood ash; the leavening-active one is largely potassium carbonate (K₂CO₃). Pearlash is a more purified, stronger, whiter version historically sold to bakers. Both act as bases: add an acid and you get carbon dioxide to lift your bake.

How the Leavening Works (Plain-English Chemistry)

• Base (potash/pearlash) + acid (vinegar, buttermilk, molasses) → CO₂ gas
• Gas bubbles expand with heat → tender crumb in flat cakes, cookies, fritters
• Too much base without enough acid → soapy/bitter taste (neutralize carefully!)

Where You’ll See It in Old Recipes

• Gingerbread & spice cakes (the molasses provides natural acidity)
• Crullers, rusks, jumbles and other early cookies/biscuits
• Early American and 18th–19th c. English-language cookbooks

Safety First ⚠️

Do not attempt to make food-grade potash from fireplace ash at home. Ash lyes can contain caustic hydroxides and impurities. For historical demonstrations, use food-grade ingredients only, and avoid direct skin/eye contact with alkaline solutions.

Good news: you don’t need ash to explore the technique—see the modern substitutions below.

Modern Kitchen Substitutions (For Historic Recipes)

When an old recipe calls for pearlash or potash, use one of these practical, grocery-available stand-ins:

If recipe says…	Use instead…	Notes
1 tsp pearlash (potash)	3/4 tsp baking soda + adequate acid (e.g., 2 tsp vinegar or buttermilk)	Start small; adjust acid to prevent soapy taste. Molasses-based doughs often need no extra acid.
“Saleratus”	Baking soda 1:1	Saleratus is an old term for sodium bicarbonate.
Pearlash in crisp cookies	Baking powder (as directed) or soda + acid	Baking powder is milder-tasting; test a half-batch to match spread/texture.

Tip: When swapping, mix the acid into your wet ingredients and the base into your dry, then combine quickly and bake promptly.

Timeline: From Ash to Tin

• Medieval–Early Modern: Ash-derived alkalis used in lye processing; occasional culinary use where acid + alkali reactions occur.
• 18th–early 19th c.: Pearlash gains popularity in Anglo-American baking (gingerbread, jumbles, crullers).
• Mid–19th c.: Saleratus (sodium bicarbonate) becomes common; early commercial baking powders follow.
• Late 19th–20th c.: Double-acting baking powders dominate home baking; potash leavening fades from kitchens.

FAQ: Potash & Historical Leavening

Is potash the same as pearlash?

Pearlash is a refined, bakery-ready form of potash (primarily potassium carbonate). It’s stronger, cleaner, and whiter than crude potash.

Is potash the same as lye?

Not exactly. “Lye” typically refers to caustic alkaline solutions (often sodium or potassium hydroxide). Potash used for leavening is mostly potassium carbonate, which is still alkaline but less caustic than hydroxide solutions.

Can I make food-grade potash from my fireplace ash?

No—please don’t. Impurities and caustics make it unsafe. Use grocery baking soda + an acid, or specialized food-grade ingredients from reputable suppliers if you’re doing a strict historical demo.

What recipes benefit most from pearlash-style leavening?

Gingerbreads and thin cookies where a quick, dry lift is helpful and molasses or vinegar provides built-in acidity.

Related:

• Spice Measurement FAQ – Ounces to Tablespoons
• Spice Substitution Chart

🥖 Forgotten Leaveners Series

This article is part of our series exploring the strange and fascinating ways breads and cakes were raised before modern baking powder.

• From Ashes to Antlers: Forgotten Leaveners Before Baking Powder – overview & series intro
• Potash & Pearl Ash: The Alkaline Origins of American Baking
• Potash: The Ashes That Raised a Nation
• Potash Leavening — Historical Baking with Ashes (Before Baking Powder)
• Egg Leaveners: From Renaissance Biscottini to Modern Baking

📜 Sources & Notes

• Anglo-American confectionery & baking manuals (18th–19th c.) on pearlash and saleratus
• Historical chemistry texts on potassium salts from wood ash and their domestic uses
• Modern food science notes on acid-base leavening and CO₂ production