RAISING AGENTS fall into three specific categories:Chemical, Mechanical and Natural
The main two Chemical Leaveners used in Baking are:
Baking Powder and Baking Soda.
Baking Powder is a blend of acid (most commonly calcium acid phosphate, sodium aluminium sulphate or cream of tartar) and alkali – (baking soda/sodium bicarbonate). These create carbon dioxide bubbles when liquid and heat are added.
Commercial baking powder uses several compounds which gives it a double action. It acts when liquid is added and once again when heat is added after you put your product in the oven.
You can make up your own baking powder raising agent - for one teaspoon: mix 1/2 teaspoon cream of tartar with 1/4 teaspoon baking soda. If you decide to mix up your own BE AWARE! You must put your product straight into the oven - the addition of liquid starts the chemical reaction. If you leave it standing pre-baking, your 'Home-Made' raising agent will be ‘spent’ before baking starts. Unlike commercial baking powder, it only has the one action – when you add moisture.
Baking Soda (Bicarbonate of Soda), is used when there is already an acid ingredient in the recipe such as:
Applesauce, buttermilk, brown sugar, chocolate, cocoa powder, cream of tartar, honey, lemon juice, molasses, vinegar.
When baking soda comes in contact with an acid and liquid is added, carbon dioxide (CO2), water and a neutral salt are produced. Care must be taken with how much baking soda is used. If too much - a ‘soapy’ aftertaste remains and the product bakes darker. If not enough is used - an acid flavour remains.
Baking soda is much stronger than baking powder. The general rule is to use 1 to 1-1/4 teaspoons baking powder per half cup of flour, (4ozs/100g). Baking soda should be added at 1/4 teaspoon per half cup of flour, (4ozs/100g).
How do these chemical leaveners work?
When carbon dioxide is released by either baking soda and/or baking powder, it first dissolves in the liquid. When this becomes saturated, the carbon dioxide produced turns into the air bubbles which expand. Towards the end of baking the bubbles set. You have a well risen product showing tiny air holes when cut.
Nb. At higher altitudes less baking powder/soda is required. Low pressure has an effect on carbon dioxide and makes it expand more. If you do not use less Raising Agent your baking will end up with a poor texture.
The physical actions of creaming, kneading, beating, and whisking will incorporate tiny air bubbles which expand when heat is added. The addition of flour gives structure for the air bubbles to work against - you get rise. This structure is fixed in the oven by heat.
Creaming Method: Fat and sugar are creamed together until the sugar crystals melt and the whole mass takes on the consistency of whipped cream. Use castor sugar which has a small crystal size. It will combine with the fat far easier than granulated sugar, which has a larger crystal. The creaming method incorporates air into the mixture which is held in place by the semi-solid fat. These bubbles expand during baking allowing the batter to rise. Care must be taken once flour is added. This should be folded in carefully to avoid development of the gluten lattice structure. You will get a cake with a better texture and more rise by using special cake flours here - they are low in gluten.
Kneading is a process used in bread making. Yeast liquid is dispersed into high gluten flour to make a dough. The mechanical action of kneading the dough, either by hand or machine, develops the gluten strands which form into a lattice structure. As gentle warmth is applied, carbon dioxide is released by the yeast and is trapped in pockets, These continue to expand until heat is applied during baking. Heat kills the yeast off and fixes the gluten's lattice structure in place, which leaves you with a well-risen, light, loaf.
Beating: Certain procedures in baking require you to use a ‘beating’ method – generally where heat is involved. If you are making Hot Water Crust Pastry you would bring water and butter to the simmer stage in a pan. Flour is added and the ‘batter’ is beaten until combined. Use as the pastry for ‘Raised’ Pies. This pastry has a much stronger structure allowing pies to be cooked without a tin. The same principal applies when making Choux Pastry. Flour is added to a hot water/butter mixture. Raw egg is then beaten in. The egg gives the rise with this pastry.
Whisking: When volume has to be added then the whisking method is used. Meringues are made by whisking egg whites with sugar until the volume is six to eight times more than you began with. Gentle heat applied over several hours dries out the meringue and leaves a crisp, sweet confection. Fatless sponge cakes require whole egg and sugar to be whisked together to achieve a high volume. Cake flour is gently folded in. Air incorporated into the egg gives volume and lightness to the cake.
Yeast is a natural leavener. Give it food, moisture, warmth and air and it will grow. During this ‘fermentation’ process the carbon dioxide gas released by it is trapped in tiny air cells. These continue to expand and push up against the latticed gluten structure and you have rise! The lattice structure is formed and developed when water is added to the wheat protein (gluten), and then kneaded together.
It takes about 2 hours using fresh, active dry, or, instant active dry yeast, for the bread to complete this proving stage. The baking process stops the action of yeast cells by killing them and fixing the lattice structure of the wheat protein (gluten). Sourdough – a natural process using air borne yeast cells can take up to 24 hours to reach the stage for baking. This lengthy process produces bread with a wonderful aroma and flavour.
Eggs are another natural raising agent. The white of egg (albumen) is whisked up with sugar until it is six to eight times its volume. Again, the addition of heat causes the albumen to coagulate and fixes the structure in place. The yolk of the egg when whisked with sugar again expands in volume by air being incorporated into it. The addition of flour gives the structure which hold the air bubbles in place.
Eggs have many uses in baking. They make things rise such as in soufflés and sponge cakes. They can thicken as in custards and sauces. They can be used to add a lovely finishing colour to pastries. They emulsify and soften texture. With frostings, eggs stop the sugar from crystallising. In general, eggs add colour, flavour, richness, and they lighten the mixture.
Eggs come in different sizes though most recipes call for a large egg to be used – which is 2ozs (50g) in weight. The yolk is 1/3rd of the egg, the white 2/3rds. The yolk contains all of the fat and most of the nutrients while the white contains albumen. Care must be taken in using fresh eggs due to a problem with Salmonella. Raw egg should not be eaten. If raw egg is to be used for eating without cooking, it should be pasteurised. In Baking, this is not usually a problem as significant heat is usually applied.
There are other eggs available than hen eggs. The most common being duck, goose and quail. They are not the easiest to use in baking as the fat content is significantly higher making them far richer. This causes issues with liquid to fat ratio in recipes.
Steam is the most basic of raising agents, but also the most complex in technique. In puff pastry, the layers of butter and pastry are heated. The butter lets off steam which pushes up against the pastry leaves and you get rise. Once the steam has evaporated, the pastry leaves are set in place by heat during baking. With choux pastry and Yorkshire puddings, steam is released from the wet batter which pushes up against the gluten lattice and you get a puffed up pastry, again, fixed by the heat of the oven. In both cases, strong flour is necessary to give a lattice structure which will not break through the force of steam.
All raising agents (leaveners) work on the same principal, be it Chemical, Mechanical or Natural. Gasses expand, push up against a structure, you get rise, which is fixed by the heat of the oven. It is by using ingredients and baking techniques in the correct manner which ensures success when you Bake. Simple!