Leavening is the process by which the dough, for various reasons, increases in volume, in fact there are three types: physical, biological and chemical.
In this article we examine chemical leavening in depth and focus in particular on one of the three pillars of this type of leavening, ammonium bicarbonate, often incorrectly called “ammonia”. We indicate its correct use and point out the main differences between it and better-known chemical yeasts available on the market.
This article was written in collaboration with Alessio Busi, an established food technologist who continuously works to increase the wealth of knowledge in the baking sector, through consultancy and theoretical-practical manuals created together with his father, Omar Busi.
The three types of leavening
As we have just said, there are three types of leavening: physical, biological and chemical.
Physical leavening is essentially linked to physical phenomena such as the increase in the volume of air during cooking, the evaporation of water, or the incorporation of air during kneading. Typical examples of physical leavening are puff pastry or whipped egg whites.
Biological leavening is linked to biological phenomena, in particular the production of gas by microorganisms during fermentation. All products that contain brewer’s yeast or sourdough starters use biological leavening.
Chemical leavening is also associated with the production of gas within the dough, but the origin is not biological. Gases are produced by chemical reactions between the ingredients, which can be one of two types:
- Neutralisation, i.e. the reaction between an acid and a base which leads to the production of gas (A+B → C+D+…). A “homemade” example is the reaction between vinegar and bicarbonate of soda which is often (erroneously) recommended for cleaning the house. As regards to leavening however, all the raising agents on the market which, despite having various nomenclatures are basically the same as each other, chemical yeast, baking powder, baking powder, etc., are formulated with this criterion,
The basic substance which is the source of the gas, is almost always sodium bicarbonate. Originally the acidic substance that caused the reaction was cream of tartar, but today disodium diphosphate is much more widely used.
- Decomposition, i.e. the splitting of a molecule which generates two or more products (A → B+C+…). An example from daily lifeis to be found in the use of hydrogen peroxide as a disinfectant (the “bubbles” it produces are essentially gaseous oxygen). In the world of chemical leavening, sodium bicarbonate and ammonium bicarbonate belong to this category.
Many cakes, all-in mix sponges and some kinds of dry biscuits are made using one of these two types of chemical leavening. Not all raising agents are the same and we should be aware of their qualities in order to use them properly in recipes.
What is ammonium bicarbonate?
Known more commonly as “baking ammonia”, ammonium bicarbonate often generates confusion and fear because it is instinctively associated with the more famous “ammonia” for household cleaning. However, these are two conceptually different products which, when used correctly, present no danger to health.
What is the difference between baking ammonia and ammonia for cleaning?
Ammonia (chemical formula NH4) exists in nature in the form of a gas with a characteristic pungent odor. The liquid product used for household cleaning is simply ammonia (NH4) dissolved in water. In pastry making, it is used in gaseous form, released by the decomposition of ammonium bicarbonate (chemical formula (NH4)HCO3), a food additive authorized and strictly regulated by the European Union (code E503), which activates at 36 °C and evaporates completely at 60 °C leaving absolutely no trace in the food.
(NH4)HCO3 → NH3 + CO2 + H2O
This reaction produces a significant quantity of gas: ammonia (NH3), carbon dioxide (CO2) and water vapor (H2O). Consider that 2g of ammonium bicarbonate can produce a total of more than 1 litre of gas. For this reason it is particularly useful in the baking of dunking biscuits, which require vigorous leavening to obtain an open and airy structure, perfect for absorbing liquids.
How to use ammonium bicarbonate
If you are a pastry enthusiast or a budding professional, you may have asked yourself “How do you use ammonia in baking?” or “Is baking ammonia bad for you?”. To use ammonium bicarbonate correctly and safely, you just need to know its nature.
First of all, its relatively low activation temperature means that you must make sure not to activate it prematurely during processing so that it doesn’t lose part of its leavening power. In fact, it is good practice to add it as the last ingredient, whilst trying to keep the temperature of the dough under control.
Furthermore, it is important not to let it come into contact with the liquids in the recipe prematurely. Ammonium bicarbonate is a white powder, so a useful tip could be to incorporate it into other dried ingredients, such as flour or starch, to keep it dry and bring it into contact with the wet ingredients as late as possible.
Finally, during cooking it is normal for a very strong acrid, pungent odor to be released, which it is best not to inhale in large quantities as ammonia is toxic in high concentrations. However, the presence of residues in the product should cause no concern, once 60 °C is reached, in a dry environment, ammonium bicarbonate decomposes completely and evaporates, leaving no trace in the food.
However, since ammonia is extremely soluble in water, it is important that the product is dried out carefully in the oven. If more than 3-4% of residual humidity remains, some of the ammonia dissolves in the water instead of evaporating, transmitting an unwanted aftertaste and limiting leavening. This is why it is not recommended to use ammonium bicarbonate in moist desserts (e.g. sponges, cakes, etc.), but better reserved for use in extremely dry products (e.g. biscuits, crackers, etc. ).
The recommended dose of ammonium bicarbonate varies between 0.5% and 1.5% of the weight of the flour, depending on the desired structure. A low dosage generates a moderate leavening which translates into greater friability of the biscuit, without creating real honeycombing. A good example is cantucci, dry, crumbly biscuits with a compact structure.
A high dosage produces more significant leavening, which translates into a more open structure with evident honeycombing. This is typical of dunking biscuits, which should easily absorb the liquids into which they are immersed.
It is important not to use too much ammonium bicarbonate to avoid excessive development in the oven, which often results in the loss of shape and extreme fragility of the product.
Alessio Busi
