Chemical leaveners / raising agents


There are several ways in which to get breads, cakes and other baked goods to rise. Some of these methods have been used for hundreds of years, such as yeast or whipped eggs, and some are a very modern introduction (chemical raising agents).

Types of chemical leaveners/raising agents

Leaveners can be classed as natural, chemical or mechanical. Natural includes eggs and yeast, chemical is bicarbonate of soda, cream of tartar etc and mechanical includes the incorporation of air by physical methods (eg whipping cream or eggs) or rise created by steam or dry heat [steam/heat could also be classed as natural].

What exactly am I rambling on about

I’m only covering chemical leaveners/raising agents in this piece. I’ve actually been researching and reading up on this on and off (not continually!) for over a year now. I never imaged there was so much to it.

I set out to discover why and how chemical raising agents work in my baking. I’ve read through chemical formulas, explanations of the chemical process involved and undergraduate-level books detailing experiments all to get to here. Some of it I didn’t grasp at all, some made sense at the time but now I’m a bit fuzzy on it and plenty did made sense. I’m no scientist, so I think there’s little point in me simply regurgitating the really complex areas I’ve researched or even drawing out the chemical formulas and reactions that are involved. I might get such specific details wrong. I may not have understood it all fully. There’s a chance I could misinterpret it. So, all I’m aiming to do here is pass on what I’ve come to understand through this research about what is going on inside my cake (or other bake)  to make it rise, and if there is anything I can do to get the best results in my kitchen using raising agents.

Which raising agents

In the UK we tend to only use bicarbonate of soda as a chemical raising agent (though others are available – see later).

In a commercial baking setting (in the UK to some extent but more commonly elsewhere) sometimes baking ammonia is used instead as it produces a drier food product but it does produce a little ammonia as a by-product of the chemical reaction. You may have come across its common/historical name of ‘hartshorn’. Baking ammonia’s use in cooking predates that of bicarbonate of soda.

You’re going to say, “What about Baking Powder?”

Well, baking powder isn’t one thing. It’s a pre-mixed product of bicarbonate and a powdered acid (in its most basic, truest sense). All the information I’ve written below on the basics of how bicarbonate works also relates to baking powder, apart from two important caveats:

  • you don’t have to manually add an acid (such as lemon juice) separately as it’s already included. This also means the ratio of acid to bicarbonate is already measured precisely for you
  • the addition of a third ingredient in some commercial baking powders is there to add a second reaction which occurs in the presence of heat. It has the effect in that the leavening process occurs ‘twice’ as it were – chemical reaction one will start to produce gases in your bake in a cold environment (ie as soon as you start mixing) and the second chemical reaction will be produced in the presence of heat (as it bakes).[In the USA most baking soda’s are “double acting baking sodas” and follow this recipe. The name “double acting” implies the two chemical processes. It’s difficult to give you a definition of what to expect with American double acting baking soda as there does not seem to be an industry standard and several chemicals appear interchangeable, dependant on the manufacturer’s “recipe” and whether the product is deemed kosher or not. You may find various combinations of acid and bicarbonate in commercial double acting baking soda, the ingredients of which can be pulled from a long list: sodium bicarbonate, sodium aluminium sulphate, acid sodium pyrophosphate, calcium acid sulphate, ammonium bicarbonate, tartaric acid to name just a few. Don’t worry about conversions of American recipes – just substitute any UK/European baking powder. The American double action isn’t twice as strong as baking powder, just it definitely uses this dual process. Its strength/potency is equivalent whether the baking powder you swap it for is single or double acting itself.]

Bicarbonate of soda is most commonly mixed with cream of tartar (this could be listed as potassium bitartrate or tartaric acid) to produce baking powder. This is a single acting baking powder. Some commercially produced baking powders will include a third chemical – as mentioned above – such as acid sodium pyrophosphate, to provide this additional, second action. Also, some commercially produced tubs of baking powder may have an added stabiliser or two to prolong shelf life and minimise reaction (and therefore spoiling) prior to use.

The basics of how bicarbonates work as a food leavener

Bicarbonate of soda/sodium bicarbonate is extremely alkaline and a chemical reaction occurs in the presence of an acid – for example, lemon juice or vinegar and some moisture. You can start the reaction with a dried acid (for example vitamin C powder or cream of tartar) but you will need to add some form of moisture.

Bicarbonate does not need heat for any chemical reaction with acid to take place.

As soon as you introduce the acid to bicarbonate (in the presence of a little moisture – there may even be enough in the air) the reaction will start. What this means for your bake is that the rise starts happening as soon as you start mixing. When using a chemical leavener get your bake in the oven as soon as you can – don’t leave your mix hanging about in the bowl before you use it as you’ll have ‘wasted’ some of the chemical reaction.

We know it as baking powder in the UK, but it’s also called baking soda (typically in the US and Canada), bread soda and cooking soda. Can be listed as sodium bicarbonate or sodium hydrogen carbonate and you can spot it on a list of ingredients as E500.

The trick to using bicarbonate of soda (and baking powder for that matter, but to a lesser extent) within baking and cooking is to perfectly balance the amount of bicarbonate to the amount of acid.

In the presence of an acid, bicarbonate starts to react and one of the products produced by this reaction is carbon dioxide; a gas. It’s this release of gas bubbles that causes the rise within your baking.

For example, if you used a vinegar (which is acetic acid) with your bicarbonate, the reaction would produce some water, carbon dioxide and a small amount of sodium acetate.

Note on bakers ammonia/ammonium carbonate: for ammonium carbonate the comparable reaction produces (a little less) water, carbon dioxide and ammonia. It does not need an acid to react but does need heat and moisture. As it produces ammonia as a by-product, its use at home should not be in large quantities. When included in a mass-produced product by a commercial food company the large amounts involved (and therefore larger amounts of released ammonia) can be controlled safely in a factory environment.

The reason it is still used rather than baking powder is all because of that drier baked result – so it’s typical to find baking ammonia in things like crackers and harder biscuits. If you’re looking out for it (to be nosey) on a product’s ingredients list it may well be included as E503 rather than named. Italian, German and Scandinavian recipes in particular are most likely to include baking ammonia. I have had success in directly substituting the same amount of bicarbonate of soda for ammonium bicarbonate within a recipe, reducing any liquid in the recipe by a small amount and replacing it with an acid (for example this could be as simple as using a teaspoon less of water and adding a teaspoon of lemon juice in its place) to recreate that drier texture and effect the chemical process.

However, as a caveat, if you are similarly trying to convert one of these recipes you may need some trial and error to get this balance right yourself. I have not yet attempted to bake with baking ammonia – I’m a little nervy of the ammonia if I’m honest! I may try to get some as it is available to buy online and, if so, I will update this post with how I got on.

It’s crucial that the amount of acid used balances out the amount of bicarbonate. Too little acid or a heavy hand with the bicarbonate and not all of the bicarbonate will be able to react. This will leave some bicarbonate behind, and you’ll notice that tell-tale alkaline-salty tang which can ruin a bake. Additionally, your bake may not be fully risen either if not enough carbon dioxide was produced.

If there is too much acid the reaction can happen at a facilitated rate and also you’ll be left with a very sharp tasting bake.

Even if there is too much acid the chemical reaction will still take place but it will start more vigorously and be over quicker. This sounds OK doesn’t it? Well, actually it’s not great news for the baker, as the reaction is quick and the gas is produced faster it will start to dissipate early and the rise it produced can go to waste.

For instance, when making a cake you need the bubbles from the gas to be captured as tiny cavities in the sponge mix as it cooks. Bubbles of gas will reach their maximum size within the sponge before dispersing as the cake heats up in the oven. In a perfect bake, as the cake mix hardens around the bubbles so the cake stays light and airy once fully baked.img_1933

If your cake mix is still too soggy as the gas escapes (because the gas is escaping early) the sponge around the bubbles cannot support itself and the cake structure will collapse causing a denser, flatter bake. This will also happen if you’ve included the perfect amount of acid but have left your baking around for a while before you get it in the oven – the process will be over before you need it to be.

[Incidentally, the carbon dioxide is not the only thing that contributes to the creation of bubbles in the cake batter. Water from both the ingredients and the bicarbonate chemical reaction will be heated in the oven and start to steam, the steam expands also creating holes in the batter before evaporating.]

If we can understand the basics of how bicarbonate works, the principle will be roughly the same for baking powder

There are several reasons that baking powder is more prevalent in kitchens and more common in recipes:

  • Firstly, on its own, bicarbonate can leave that salty tang behind. It’s difficult to get the exactly perfect ratio of acid to bicarbonate as there are so many contributing factors. These are just a few examples – there could be many more reasons:
    your flour may be slightly damper than the one in the original recipe, causing the reaction to behave differently
  • You may be using a lemon juice or other acid which is more acidic than the original. This may sound odd, but for example any vinegar isn’t just acid – that’d be incredibly toxic and more dangerous than the bleach you put down your sink. Most vinegars are around just 5% acetic acid.
  • Your bicarbonate could be fairly old, have had some exposure to moisture and therefore not be as vigorous
  • All the other ingredients ‘muddy the waters’ as they cannot be relied on to have certain PH values or moisture content and therefore will impact the reaction
  • All these things (plus lost of other factors such as the humidity in your kitchen, how accurate your oven etc) mean that if the original recipe by the chef or cook worked perfectly, yours still may taste of bicarbonate, just because some teensy tiny change, even one out of your control, altered the chemical reaction

For large quantities the risk of that bicarbonate of soda taste appearing becomes greater.
It can actually discolour your baking too: bicarbonate does have a tendency to turn things yellow/green (have you ever put a spoonful of bicarbonate of soda in a glass of red fruit squash? It’ll go a dark purple).

All these things make ‘pre-loading’ bicarbonate of soda with an acid, in a controlled ratio a much more sensible option – hence the development of baking powder.

Baking powder (as mentioned previously) is a mix of sodium bicarbonate and tartaric acid. This means the ratio of bicarbonate to acid is better controlled. By using baking powder, your bake will then be less affected by other ingredients and whether you’re heavy handed with the lemon juice.

In commercial baking powder: this stuff you buy from the supermarket or grocer you’ll often find a stabilising agent in there too such as cornflour (cornstarch) or flour and there may be some other phosphates added (these are harmless).

The cornflour is in there to keep the bicarbonate dry (to avoid any chemical reaction starting), stop it from caking and to help aid the shelf life of the product.

As an alternative, make your own baking powder! You can make it as you need it and it’ll be fresh and ready to start its chemical reaction in your bake.

The ratio is 2 parts bicarbonate of soda to 1 part cream of tartar.

If your recipe calls for 1 teaspoon of baking powder:

2/3 teaspoon bicarbonate of soda and 1/3 teaspoon cream of tartar

If your recipes calls for 1 1/2 teaspoons of baking powder

1 teaspoon bicarbonate of soda and 1/2 teaspoon cream of tartar

You can double up on those if your recipe needs more….

So… why do some recipes need both baking powder and bicarbonate of soda?

This is because they include a very acidic ingredient (or more than one), such as lemon juice or buttermilk, which is needed for taste or consistency. If a recipe has a lot of acidic ingredients it would not be very pleasant to eat if the acidity level wasn’t countered with just baking powder, so the additional bicarbonate of soda is added for that purpose. Of course, this means that the chemical reactions are magnified and give more rise to the recipe, so although a recipe may have both raising agents they probably are not in much higher quantities than a typical bake. Recipes with both in will have been tested and worked out so that there is a balance between ingredient acidity levels, the perfect amount of rise required and the amount of leaveners used all at the recipe development stage.

Conclusions – what does this all mean to the home baker?

If you follow anything exactly in a recipe make sure you stick to the exact amount of baking powder (or bicarbonate) that the recipe states. The recipe developer has worked it all out and tested the bake to ensure it’s correct. Even a little deviation could leave you with an alkaline or acid-tasting bake or one that hasn’t risen sufficiently or, indeed, that’s risen too fast and then collapsed.

Keep some shop-bought baking powder in your cupboard – you don’t always need to make it yourself. Do check the label next time you buy to make sure that anything other than an acid and bicarbonate on the ingredient list is only cornstarch or something you yourself believe to be safe. If in doubt go for a reliable, ethical brand like Dove Farm.

Keep a pot of both bicarbonate of soda and cream of tartar in your kitchen as well. You can then make your own baking powder for a change, to ensure it’s as fresh as possible (to get the best leavening result) or at least now you know how to make it if you run out.

Made a bake and you can taste the soda? Next time you make it reduce the bicarbonate of soda by 1/2 a teaspoon or add in 1/2 teaspoon of lemon juice  (or yoghurt or vinegar etc, dependant on the type of savoury or sweet bake). If the recipe only has baking powder listed just add the extra acid or a 1/4 teaspoon of cream of tartar.

Make sure you keep your tubs of baking powder, bicarbonate and cream of tartar well sealed and away from moisture.

If you’re using chemical leaveners/raising agents get your bake in the oven as soon as it is mixed. While you are mixing the chemical processes are already starting. In order to get the back in as soon as it is ready you should ensure that your oven is up to temperature you require before you start to mix.

Making your own self-raising flour

Self-raising flour isn’t made any differently than plain flour of the same grade: it’s just got the leavening agents already added in. Of course you can get ‘supreme sponge flour’ which is ready sieved  – this just means it’s been fluffed up through a sieve to ensure there are no clumps. If you buy a finer milled plain flour it’s just the same thing as this ‘supreme sponge flour’ just without the raising agents added. Self raising flour is NOT produced differently to plain apart from the extra sieving for the ‘supreme’ flours, but that’s post production and not part of the actual milling. It is only the addition of raising agents (and other extra ingredients as the manufacturers see fit) that makes the difference.

Many well known brands put additional ingredients into their flours other than the raising agents. These are not sinister or harmful but are there to increase shelf life, stop moisture retention, reduce clumping or are just added vitamins and minerals. However, if you make your own self raising flour you won’t need all these – just the bare minimum of ingredients.

None of these additives are harmful or unsuitable for vegans/those careful with ingredients for religious reasons. If you’re not too fussed, then that’s all fine, but personally even though these ingredients are not harmful I do not really want anything that’s not needed. All I need in my self-raising flour is flour, sodium bicarbonate and tartaric acid.

Some of the added ingredients are actually vitamins and minerals, which also seems good but to me I wonder why we need them added to flour of all things. I don’t really expect to get vitamin C from baked goods and I’d prefer it to come fresh from any fruit or veg (I can even ensure I add them into my bakes – that’s a better way to add it!).

Other things you may find on the ingredients label on your flour packet include ‘sodium hydrogen carbonate’. This is just another name for bicarbonate of soda, so of course you’d expect to see that listed.

It is also not unusual to find calcium phosphate, monocalcium phosphate and disodium diphosphate in UK self-raising flour. Calcium phosphate and monocalcium phosphate are the same thing and may appear as E341. Disodium diphosphate is E450. All these phosphates are made commercially from vegan sources and are harmless.

Even though none of these ingredients is a worry, maybe you still fancy making your own self-raising flour? You’ll know what you’ve put into it and it gets you used to making it rather than having to buy two separate types of flour.

Ingredients – self-raising flour

The ratio for self-raising flour is to use 20 parts of plain flour to 1 part baking powder

Therefore, for each 100g of plain flour add 1 level teaspoon of baking powder

(See above for the make-it-yourself baking powder recipe)



  1. Wow, what a brilliant post to read. The fact that I was a laboratory analyst made all the details more appealing. I stopped buying self raising flour when I really started developing my own recipes. For the reasons you’ve stated, it allowed me to have more control over a new recipe, with added factors such as eggs etc. I try to keep as many un-needed ingredients out of my baking as possible. Really enjoy reading through this.

    Liked by 1 person

    • Just my train of thought Sammie – i like that level of control, plus it’s cheaper and there are fewer things in my kitchen. This is rather essential as it’s a bit restricted in here. Thank you for such a lovely comment and the time taken xx


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