Foundations · Article 25

Chemical Leavening

A reference article · 4300 words · 41 cited sources · last reviewed September 2026

Ingredient Science explains what soda and baking powder are. This article supplies what it leaves out: the arithmetic that lets you write a leavening line from scratch, balance it against the acids already in the formula, and read a soapy, yellowed, or collapsed result for what it is.

Every chemically leavened bake is a small acid-base reaction run inside a batter, and it either comes out balanced or it does not. Balanced, the bicarbonate is fully consumed, the crumb sits near neutral, and the gas arrives during the minutes in the oven between the batter loosening and the crumb setting. Unbalanced one way, unreacted soda decomposes in the heat and leaves sodium carbonate behind: the soapy taste, the yellow tint, the too-fast browning. Unbalanced the other way, the crumb is sour and dense. The difference is measurable, and the measurements are not hard to use.

What a gram of soda can do

Sodium bicarbonate releases carbon dioxide two ways, and only one of them is what you want. With an acid and water present, one molecule of bicarbonate gives one molecule of CO₂ and leaves a neutral salt. Heated without acid, it decomposes on its own, yields half as much gas per gram, and leaves sodium carbonate, which is strongly alkaline, in the crumb (McGee, 2004). The theoretical yield with acid is the ratio of the two molar masses, 44 over 84, or 0.52 g of CO₂ per gram of soda, the figure BAKERpedia and the American Society of Baking both publish. Potassium bicarbonate, the sodium-free substitute, yields 0.44; ammonium bicarbonate, the baker’s ammonia of thin cookies, yields 0.56 (BAKERpedia, n.d.-a).

A double-acting baking powder packages the soda with a fast acid, a slow acid, and a starch buffer. Figoni’s from-scratch version is 30 g soda, 70 g cream of tartar, and 15 g cornstarch, which works out to 26 percent soda and, at cream of tartar’s neutralizing value, is almost exactly balanced (Figoni, 2011, via Lawandi, n.d.). That is why the substitution rules all agree that a teaspoon of powder carries about a quarter teaspoon of soda (Corriher, 2008; Lee, 2021). American household powders pair monocalcium phosphate as the fast acid with sodium aluminum sulfate or sodium aluminum phosphate as the slow one; European powders pair it with sodium acid pyrophosphate (BAKERpedia, n.d.-b).

Neutralizing value

The number that lets you balance acid against soda is the neutralizing value, defined as the parts by weight of sodium bicarbonate that 100 parts of the acid will neutralize (BAKERpedia, n.d.-a; Innophos, n.d.). The formula used identically by BAKERpedia and ICL Food Specialties is acid needed = soda × 100 ÷ NV. Ten grams of soda calls for 12.5 g of monocalcium phosphate (NV 80) or 22 g of cream of tartar (NV 45). An acid with NV 100 is used gram for gram with soda.

Two of the published values do not reconcile and are worth knowing about. Sodium acid pyrophosphate is 72 in every source, including BAKERpedia’s own formulation table, except BAKERpedia’s SAPP entry, which says 70; industry uses 72. And BAKERpedia lists citric acid at 159, which exceeds the stoichiometric ceiling for a triprotic acid of that molar mass; the calculated maximum is 131, and that is the figure used here.

Neutralizing value is a stoichiometric quantity. It tells you how much acid is eventually consumed, not when. Two acids with the same value can behave completely differently in the oven, which is the subject of the next section, and a balanced formula finishes near neutral pH, which is the design goal of every commercial powder (Innophos, n.d.). An acid in excess carries its own flavor: McGee notes that sulfates and pyrophosphates are distinctly astringent (McGee, 2004).

Rate of reaction

The industry measure is the dough rate of reaction: the percentage of an acid’s available gas released during mixing, during a bench rest at 27 °C, and in the oven (Innophos, n.d.; ICL Food Specialties, 2025). Innophos publishes the profile for its own products, and the spread is the whole story of leavening design. Monocalcium phosphate monohydrate releases 60 percent of its gas in the mixer and the rest in the oven. Dicalcium phosphate dihydrate releases nothing until heated. Sodium aluminum phosphate releases 22 percent in the mixer, 9 on the bench, and 69 in the oven. Sodium acid pyrophosphate grades run from 22 to 36 percent in the mixer with the balance in the oven, and the grade number, 26, 28, 40, is a nominal reading of that mixer-stage release: “higher numbers indicate a faster rate of reaction” (ICL Food Specialties, 2025). Glucono-delta-lactone is the slow, temperature-driven acid of the set, about 10 percent at two minutes, 20 at ten, and 70 in the oven (American Society of Baking, n.d.).

Bellido, Scanlon, Sapirstein, and Page (2008) put the rate test on a pressuremeter and found that GDL and adipic acid follow first-order kinetics while potassium acid tartrate and SAPP fit a two-fraction model, one fast and one slow, which is the kinetic signature of double-acting behavior inside a single acid.

Why timing matters more than quantity was shown directly by Godefroidt, Ooms, Bosmans, Brijs, and Delcour (2021), who baked cream cakes in an electrical-resistance oven while monitoring the headspace gas. Early-acting organic acids released much of their CO₂ in the mixer, where it could not be held, and gave low-volume cakes. SAPP and the late-acting acids gave high-quality cakes. Gas produced after the crumb had set was simply wasted. The window that counts opens when the batter goes in and closes when starch gelatinization and protein coagulation fix the structure, and a leavening acid is chosen for how much of its gas lands inside it. This is also why a from-scratch soda-and-cream-of-tartar blend, which is fast and single-acting, has to be baked at once, while a SAPP or SALP powder tolerates a rest.

How much

For converting the rules that follow, a teaspoon of baking powder weighs 4 g (King Arthur Baking, n.d.) and a teaspoon of baking soda 4.6 g (USDA, n.d.); a US cup of all-purpose flour is taken at 125 g, the figure the per-cup rules assume.

The home rule, stated by Corriher and attributed to Figoni, is 1 to 1¼ teaspoons of baking powder per cup of flour and, where soda is used, ¼ teaspoon per cup with enough acid to consume it (Corriher, 2008; Lawandi, n.d.). Pastry Arts gives the same band by weight, five to six grams of powder or one gram of soda per 125 g of flour (Kohout, n.d.). In baker’s percentage that is about 3.2 to 4 percent powder and about 1 percent soda.

Professional formulas run higher. Gisslen’s muffins carry 6 percent powder, his biscuits 6, his scones about 5, his pancakes nearly 7, and his creaming-method yellow cake 5; where buttermilk enters, the powder drops and soda appears, to 2.5 percent powder and 1.25 percent soda in the buttermilk cake, or 5 and 1.25 in buttermilk biscuits (Gisslen, 2005). BAKERpedia’s industrial guidance is 3 to 5 percent powder on flour for cakes and over 6 for scones (BAKERpedia, n.d.-b). The professional band sits above the home band because those formulas are written for pastry flour, mechanical mixing, and pans that want the extra lift; the home rule is the safer starting point for a hand-mixed all-purpose cake.

Gisslen’s governing rule is the one to carry: “The amount of soda used in a formula is generally the amount needed to balance the acid. If more leavening power is needed, baking powder, not more soda, is used” (Gisslen, 2005). And on the ceiling: “Do not include more baking powder than necessary in a formula because undesirable flavors may be created. Also, excess leavening may create an undesirably light, crumbly texture. Cakes may rise too much and then fall before they become set.”

Two experiments bracket the band. Book and Brill (2015), at a leavening-acid manufacturer, ran yellow cake at soda levels of 1.4, 3.0, and 4.6 percent of flour with neutralizing-value-balanced acid and found maximum volume at 3.0 percent, under-leavening at 1.4, and collapse at 4.6. Because their soda was balanced with acid, 3.0 percent soda is roughly 9 to 11 percent of a finished powder, a commercial high-ratio level. Asamoah and colleagues (2023, 2025) optimized powder in pound cake by response-surface methods and found volume and porosity rising with powder and then falling as the level approached 4.5 percent, with an optimum of 2.75 percent for conventional baking. The pound-cake optimum agrees with the home rule; the yellow-cake figure shows how far a commercial layer cake pushes past it.

What the recipe’s own acids can carry

When a formula leavens with soda alone, the acid is an ingredient, and the soda must not exceed what that ingredient can neutralize. McGee’s rule of thumb is the one to memorize: half a teaspoon, 2 g, of baking soda is neutralized by a cup of fermented milk, or a teaspoon of lemon juice or vinegar, or 1¼ teaspoons of cream of tartar (McGee, 2004).

The buttermilk figure can be checked. Cultured buttermilk has a titratable acidity of 0.88 to 0.95 percent as lactic acid and a pH of 4.3 to 4.6 (Gettys & Davidson, 1985); the international standard floor is 0.60 percent (Libudzisz & Stepaniak, 2002). A cup of buttermilk at 0.9 percent carries 2.2 g of lactic acid, and neutralizing it takes 2.05 g of bicarbonate, which is McGee’s 2 g and about half a teaspoon. At the 0.60 percent floor the figure falls to 1.4 g, a third of a teaspoon. The rule sits at the acidic end of real buttermilk, so a milder product leaves a little soda unreacted. Sour cream is defined at not less than 0.5 percent titratable acidity (21 CFR 131.160) and yogurt at pH 4.6 or below (21 CFR 131.200), which makes the half-teaspoon figure an upper bound for those.

Natural cocoa runs pH 5.2 to 5.6; light Dutch-process 6.0 to 6.5, medium 6.5 to 7.0, heavy 7.0 to 8.0 (BAKERpedia, n.d.-c). Gisslen’s balancing table is the only published quantity: natural cocoa carries 80 g of soda per kilogram, Dutch-process none, unsweetened chocolate 50 g per kilogram, sweet chocolate 25, and “if you are substituting dutched for natural cocoa, you must increase the baking powder by 1 oz (30 g) for each ½ oz (15 g) soda omitted” (Gisslen, 2005). King Arthur’s home version of the same swap, for recipes with three tablespoons or more of cocoa: replacing Dutch with natural, use half the amount of baking soda in place of the powder; replacing natural with Dutch, use twice the amount of powder in place of the soda (Hamel, 2020). Dutch cocoa in a soda-only recipe makes no gas at all, and “the taste will be alkaline and soapy” (McGee, 2004).

Honey averages pH 3.9 but buffers weakly, and no published soda equivalence exists for it, for molasses, or for brown sugar, though all three are used as the acid in Gisslen’s molasses-muffin and gingerbread formulas at 0.75 to 1.4 percent soda. The calculator treats them as acid sources without a quantity and says so.

Substituting one system for another

Powder from soda and acid: per teaspoon of baking powder, ¼ teaspoon soda plus ½ teaspoon cream of tartar plus ¼ teaspoon cornstarch, or ¼ teaspoon soda plus ½ teaspoon lemon juice or vinegar (Lee, 2021). By neutralizing value the cream-of-tartar blend runs slightly soda-heavy, and the essential caveat is that it is single-acting: the gas is released in the bowl, and the batter must be baked at once.

Soda from powder: use three times the volume of baking powder and expect a slightly bitter note from the extra acid salts, and accept that whatever acidic ingredient the soda was meant to neutralize will now stay acidic (Lee, 2021).

Buttermilk for milk: half a teaspoon of soda per cup of buttermilk, and two teaspoons of baking powder removed for each half-teaspoon of soda added, is the home conversion consistent with the acidity data (Corriher, via For Love of the Table, 2011); Gisslen’s professional version is in the callout above.

Too much and too little

Any bicarbonate the acids cannot consume decomposes in the oven, and the crumb finishes alkaline. McGee: “a bitter, soapy, or ‘chemical’ flavor results. Colors are also affected in even slightly alkaline conditions: browning reactions are enhanced, chocolate turns reddish, and blueberries turn green” (McGee, 2004). The yellow tint of an alkaline crumb comes from flavonoids in the flour that are colorless at normal pH and yellow at high pH; the compounds have been identified as apigenin-C-diglycosides and their esters (Asenstorfer, Wang, & Mares, 2006). BAKERpedia adds coarse grain and low volume in muffins (BAKERpedia, n.d.-d). Pop (2007) baked a cake series at crumb pH 5.0, 6.5, and 8.5 and found the high-soda cake darker, coarser, and tasting “like a soap film on the tongue”; Stahl and colleagues (2009) measured commercial chocolate cake mixes finishing above pH 8.3 and recommended a finished pH no higher than about 7.25 to hold color, leavening, and cocoa flavanols in balance.

Excess leavening of any kind gives Gisslen’s “undesirably light, crumbly texture,” and a cake that rises too far and falls before it sets; Book and Brill’s 4.6 percent cake collapsed. In cookies too much powder enlarges the bubbles until they pop and the cookie bakes dense and craggy (Kohout, n.d.). Over-expansion is also the characteristic high-altitude failure, which is why the leavening cut is the first correction in Environmental Variables & Troubleshooting.

Too little gives a dense, tight crumb; in America’s Test Kitchen’s comparison, soda-only cornbread and cookies were deep brown and the cookies spread instead of rising (America’s Test Kitchen, n.d.-a). Under-neutralized acid gives a sour crumb with “a bitter aftertaste” (Pop, 2007).

Storage, potency, and baker’s ammonia

Soda, powder, and ammonia “must always be kept tightly closed when not in use. If left open, they can absorb moisture from the air and lose part of their leavening power” (Gisslen, 2005). The starch in baking powder is there to absorb that moisture and prevent premature reaction (McGee, 2004). Producers claim about a year once opened; America’s Test Kitchen found biscuits made with ten-month-old powder rose to half the height of fresh and recommends discarding an opened tin after six months (America’s Test Kitchen, n.d.-b). The test: half a teaspoon of powder in two tablespoons of warm water should foam at once, and half a teaspoon of soda in a tablespoon of vinegar should fizz immediately and vigorously (Hamel, 2015).

Ammonium bicarbonate decomposes on heating into carbon dioxide, ammonia gas, and water and leaves no salt residue, which is why it gives exceptionally crisp, light thin cookies and crackers and none of soda’s aftertaste (McGee, 2004). The ammonia has to escape, so it belongs only in small products baked until dry, under about 5 percent moisture: springerle, Leckerli, Spekulatius, crackers (Gisslen, 2005; BAKERpedia, n.d.-e). Sources differ on when it starts: McGee gives 60 °C (140 °F); BAKERpedia says above 40 °C. The practical reading is that it begins gently around 40 and is vigorous by 60. Van der Sman (2021), modeling biscuit dough thermodynamically, found that most of the gas in a soda-plus-ammonia biscuit comes from the soda, and that ammonium bicarbonate contributes less than is commonly assumed.

Aluminum, sodium, and the newer acids

Sodium aluminum sulfate and sodium aluminum phosphate are the cheap, potent, heat-triggered acids of the American household powder, and both can leave a metallic aftertaste. The aluminum-free market exists for taste and for the aluminum question, and the question is real: the aluminum in SALP is bioavailable, at about 0.11 to 0.13 percent from a baked biscuit in rats (Yokel & Florence, 2006), and a week of SALP-leavened pancakes more than doubled urinary aluminum excretion in healthy adults (Glynn & Lignell, 2019). The European Food Safety Authority re-evaluated the aluminum salts in 2018 and found no safety concern at authorized European uses, largely because European powders use SAPP and exposure by this route is “probably near zero” (EFSA ANS Panel, 2018); in the United States, where SALP remains common in pancake mixes and powders, Saiyed and Yokel (2005) measured up to 180 mg of aluminum per serving in some products. Aluminum-free powders substitute SAPP, or MCP with calcium acid phosphate, for the aluminum salt.

On the sodium side, potassium bicarbonate substituted for sodium bicarbonate in cookies matched spread and baking performance without harming sensory scores (Chen, Hu, & Li, 2019), and calcium acid pyrophosphate replaces SAPP as the acid (Gorton, 2014). Gélinas’s reviews of the patent record since 1833 show that more than half of all leavening-acid inventions concern phosphates and that the current wave is sodium-free, aluminum-free, and phosphate-free (Gélinas, 2021, 2022a, 2022b). Fat-coated, encapsulated bicarbonate holds its gas in refrigerated and frozen batters until the coating melts; the melt point of the coating governs the volume on storage (Dorko & Penfield, 1993).

A worked leavening line

A buttermilk cocoa layer cake, flour 1,000 g, buttermilk 700 g, natural cocoa 60 g. The buttermilk at 0.9 percent lactic acid carries 6.3 g of acid and can consume 5.9 g of soda; McGee’s rule gives 5.7. The cocoa at Gisslen’s 80 g per kilogram carries 4.8 g. The acids can absorb about 10.5 g of soda, just over 1 percent of flour, at the ceiling of the home band. Three teaspoons of powder do the work of one of soda, so that soda supplies gas equivalent to about 27 g, or 2.7 percent, of a finished powder, and a creaming-method cake wants 3.2 to 5 percent powder-equivalent in total, so the balance comes from baking powder at 1.5 to 2.5 percent, 15 to 25 g, per Gisslen’s rule that extra lift comes from powder and never from more soda. If any of the acid is fast, bake promptly; a SAPP or SALP powder tolerates a rest. The Leavening Calculator runs exactly this arithmetic.