E503

Ammonium Bicarbonate

Last reviewed: 7 May 2026

Traditional baker's ammonia — the oldest chemical raising agent, used where baking powder can't get the texture right.

E503 is the additive number for ammonium bicarbonate — known to bakers for several centuries as baker's ammonia, hartshorn salt or, in German recipes, hirschhornsalz. It is a fine white crystalline powder that decomposes when heated into three gases — ammonia (NH₃), carbon dioxide (CO₂) and water vapour (H₂O) — leaving nothing behind in the finished biscuit. That clean break is the whole point: it's the reason a traditional Lebkuchen, springerle or pepparkakor recipe specifies it instead of baking powder, and the reason it shows up on UK labels of hard biscuits and crackers as E503, ammonium bicarbonate or ammonium hydrogen carbonate.

What E503 actually is

The pure compound is ammonium bicarbonate, NH₄HCO₃. It crystallises as a fine white powder with a faint, sharp smell of ammonia even at room temperature — a clue to how readily it gives up that ammonia when heated. The food-grade material listed under E503 is, in practice, usually a mixture of ammonium bicarbonate together with a small fraction of ammonium carbamate (NH₂COONH₄), which is why some labels and historical references use ammonium carbonate and ammonium bicarbonatealmost interchangeably. For baking purposes the behaviour of the mixture is the same: heat it and it falls apart into ammonia, carbon dioxide and water.

Three names you will see in UK ingredient lists, all referring to the same E503 material:

• E503 — the additive number
• Ammonium bicarbonate — the most common chemical name
• Ammonium hydrogen carbonate — the IUPAC-style name some manufacturers prefer

On a continental European label you may also see E503(ii), the European code that specifies ammonium hydrogen carbonate (NH₄HCO₃) rather than the broader E503(i) ammonium carbonate designation. The two are functionally one ingredient at the bench.

The historical names — hartshorn, sal volatile, hirschhornsalz

Long before industrial chemistry produced ammonium bicarbonate from ammonia and CO₂, bakers and apothecaries got it from a more pungent source: the antlers of male red deer. Hart's horn — Old English for the antler of a male (hart) deer — was distilled in dry retorts to drive off a salt that condensed at the cool end of the apparatus. Medieval and Renaissance pharmacists called the result sal cornu cervi, the salt of the deer's horn. By the 18th century the same material went by sal volatile or spirit of hartshorn, and was used as smelling salts as well as in baking.

The German name hirschhornsalz — literally "deer-antler salt" — preserves the etymology directly. So does Scandinavian usage: in Swedish and Danish recipes you may see hjorthornssalt. None of those products contain antler today. By the mid-19th century the chemistry was understood, and ammonium bicarbonate was being produced industrially from ammonia, carbon dioxide and water. The traditional names stuck because the recipes did. A 21st-century bag of "hartshorn" or "hirschhornsalz" is the same NH₄HCO₃ you would buy as E503.

The chemistry: every product of decomposition is a gas

Heat NH₄HCO₃ above about 60 °C and it begins to come apart. Push the temperature past 80 °C and the breakdown accelerates sharply. By the time a biscuit hits a typical baking temperature of 180–200 °C the decomposition runs to completion, and the equation is simple:

NH₄HCO₃ → NH₃ + CO₂ + H₂O
(solid) → (ammonia gas) + (carbon dioxide gas) + (water vapour)

Three points worth pulling out of that one line:

• Every product is a gas. There is no solid residue, no salt, no acid byproduct. The mass that was the powder is now three gases — and on a per-gram basis, more gas than baking soda or baking powder produces.
• The decomposition is essentially complete. The combination of high oven temperature and the fact that the gases drive themselves out of the dough means the reaction does not stall halfway. EFSA's 2018 re-evaluation of the carbonates additive group rests on this: in baked goods, the additive is not present in the finished product.
• Two of the three gases are completely odourless and tasteless (CO₂ and H₂O). The third — ammonia — is the one bakers and label-readers notice, and the one that imposes the constraint on which products E503 actually fits.

Why traditional bakers prefer it over baking powder

Baking powder works. It is what a UK home baker reaches for nine times out of ten. So why do continental biscuit recipes — Lebkuchen, springerle, pepparkakor, certain shortbread-adjacent ranges, hard ginger biscuits — specifically call for baker's ammonia? Three reasons that traditional bakers will tell you in order:

• No residual salts. Baking powder leaves behind sodium and acid-reactant salts in the finished crumb. Baking soda (E500, sodium bicarbonate) leaves sodium carbonate, which can give a faintly soapy or alkaline aftertaste in any product without enough acid in the dough to neutralise it. Ammonium bicarbonate, by contrast, leaves nothing — and a thin biscuit lives or dies by its clean flavour.
• More gas per gram. Because both the ammonia and the CO₂ are gases at oven temperature (and the water flashes to steam), one gram of E503 produces a higher total gas volume than the equivalent gram of baking soda or baking powder. For traditional hard biscuits that depend on dramatic puffing as the dough hits the heat, that gas volume matters.
• A particular crispness baking powder can't match. The combination of fast gas release at relatively low temperatures (60–80 °C, well before the dough has set) and the absence of any residual salt produces a snap and crumb structure in thin biscuits that bakers describe as drier, crisper, more brittle. It's the texture of a Lebkuchen edge or a properly snappy pepparkakor — and it is hard to reproduce by substitution.

Why it only works in thin, low-moisture goods

The constraint that limits E503 to a specific corner of baking is a property of ammonia itself: ammonia is highly water-soluble. Carbon dioxide and water vapour leave a hot biscuit easily and don't come back. Ammonia, however, dissolves in any moisture it encounters, and a small amount remains dissolved in residual moisture in the crumb. In a thin biscuit — say, under about 10 mm thick — the bulk of that ammonia escapes during baking and what little remains airs out in a few hours of cooling. In a thick or moist product the ammonia gets trapped in the crumb and stays there: the result is a finished biscuit that smells, and tastes, of household cleaner.

Hence the rule of thumb that traditional bakers pass down: baker's ammonia is for biscuits, crackers, and other goods under about 10 mm thick. It is not for cakes, soft cookies, sponges, breads or anything where the crumb stays moist and dense. Use it in the wrong product and the ammonia smell is the fault, not the product. Use it in the right product and the smell is gone before you eat it.

Where you'll see it on UK biscuit labels

UK shoppers most often encounter E503 in:

• Hard, snappy biscuits — the kind that break with a clean crack rather than yielding
• Savoury crackers — particularly thin, layered or laminated cracker formats where a clean snap matters
• Traditional gingerbread and hard ginger biscuits
• Imported continental biscuits — Lebkuchen, springerle, pepparkakor, certain Italian biscotti-adjacent products, Dutch speculaas. These often appear on UK shelves around Christmas, often with original-language ingredient lists in addition to the English translation.

On the back of the pack you may see any of: raising agent: E503; raising agent: ammonium bicarbonate; raising agent: ammonium hydrogen carbonate; or, on imported packaging, the foreign-language equivalent. UK and EU regulations permit any of those as a valid declaration. They all describe the same material.

The fresh-from-the-oven ammonia smell

If you make Lebkuchen at home from a German recipe and pull the tray out of the oven, the kitchen will smell of ammonia. This is not a defect, it is not a sign of underbaking, and it does not mean the biscuits are unfinished. It is residual NH₃ evaporating from the crumb as the biscuit cools. Within a few hours — sometimes overnight — the smell is gone, and the biscuit reads as a clean spiced biscuit again.

Commercially produced biscuits go through a longer cooling and packaging process than your tray on the kitchen counter, which is why the supermarket version of an equivalent product rarely smells of ammonia at all. If a packaged biscuit does smell faintly of ammonia on opening, it usually means it was packed warmer than ideal — not that the recipe was wrong. The smell airs off in the open air; the biscuit is unaffected.

Storage and home baking

Baker's ammonia is hygroscopic — it pulls moisture from the air — and it slowly decomposes at room temperature, which is why a freshly opened tin smells faintly of ammonia even before you've used it. For that reason it is sold in airtight tins, sachets or sealed plastic packets and is best stored cool, dry, and tightly closed. It loses potency over months if left open, more slowly than that if sealed.

It is not a staple in most British home kitchens. Where you'll see UK home cooks reach for it is in translated continental recipes — German Lebkuchen, Swedish pepparkakor, Italian biscotti variants, certain Greek and Cypriot biscuits — and in heritage or specialty baking books. Specialist bakeware suppliers and continental delicatessens carry it; major UK supermarkets generally do not. If a recipe calls for hartshorn salt or hirschhornsalz, that's what to ask for.

Regulatory position

EFSA, the European Food Safety Authority, conducted a re-evaluation of the carbonates additive group — E500 (sodium carbonates), E501 (potassium carbonates) and E503 (ammonium carbonates) — in 2018. The panel concluded that there was no concern at the reported uses and use levels and did not specify a numerical Acceptable Daily Intake. Instead, the additive sits at quantum satis — Latin for "as much as is needed" — meaning it can be used at the technological level required to do its job, on the basis that the additive decomposes completely during baking and is not present in the finished food.

In the UK, ammonium bicarbonate is permitted under the retained EU food additives regulation as a raising agent. In the US, the FDA places it under its "Generally Recognized as Safe" (GRAS) classification — the federal designation for additives with a long, documented history of food use. UK label declaration may use any of E503, ammonium bicarbonate, or ammonium hydrogen carbonate.

Not the same as ammonium chloride (salmiak)

One quick disambiguation worth making, because the names confuse readers. Ammonium bicarbonate (E503) is not the same as ammonium chloride. Ammonium chloride is the salty, slightly bitter compound that gives Nordic salmiakki — salty liquorice — its characteristic flavour. It used to carry the additive number E510 in Europe but has since been delisted as a food additive in the EU; it survives in salmiak products under specific national rules. E503 is a raising agent that disappears entirely on baking. Ammonium chloride is a flavouring you can taste in the finished product. Different chemistry, different role, different additive.

What we do at NutraSafe

We treat E503 the same way we treat every additive on a UK label: when you scan a barcode in NutraSafe, we surface the additive list — including E503 wherever the manufacturer has declared it — alongside the rest of the ingredient breakdown. You can search any UK biscuit, cracker or imported continental baked good and see the additives at a glance, with a short explanation tied to each one. We don't grade products on a single letter or hide the chemistry behind a verdict; we show you what's in the food and let you read the label cleanly.