Leavening agents

A Bit About Yeast

Raising or Leavening Agents

Yeast Gluten and Carbon Dioxide

Catching Wild Yeast

Leavening Agents

A leavening agent is an organism or substance used in baked goods that causes them to rise. When added to moisture, the leavening agent reacts to produce carbon dioxide that becomes trapped as bubbles within the dough so helping it rise..

Commonly used leavening agents include: (the links are to wikepedia)

·   baker's yeast

·   sourdough

·   yogourt

·   baking powder

·   steam

·   air

·   pearlash

 A Bit About Yeast

See also

·   Yeast (baking)

·   Nutritional yeast

·   Brewing Yeast Propagation and Maintenance: Principles and Practices

Raising or Leavening agents

Organic Grain and Flour - Yeasts & Raising Agents

Yeast is an organism capable of reproducing itself which when added to bread makes it rise. Given moisture, food and warmth and time, yeast will grow producing carbon dioxide gas to rise bread dough and creating the cellular structure of breadcrumb.

Before the commercial production of leavening compounds bakers relied on their knowledge and bakery skills to make the best bread they could with the ingredients available. Good quality yeast would produce good quality doughs and bread so across the centuries bakers sought to protect and control their source of yeast as it was their livelihood.

From early times brewing and baking were often linked. Brewers ferments and by products would typically be added to ground grains or flour to make a barm that would be used to leaven bread. Dried barm or a piece of remaining unbaked dough could be moistened, reworked and added as a starter to each new baking. Today sourdough starters are used in a similar way.

Sourdough Starter

When bread is made using a cultured starter as the raising agent it is referred to as a sourdough loaf. The simplest sourdough starter is made by retaining a piece of bread dough from the last baking. If you want to avoid commercially manufactured yeast you can make your own Sourdough Starter using potatoes and rye flour. Note this is still going to contain yeast even though it will be 'wild' yeast.

1. Boil the un-peeled potatoes.
2. Mash them into the cooking water. 
3. Add remaining ingredients.
4. Cover with a cloth and leave for 3 days.
5. Use instead of yeast in your bread recipe.

For further information about sourdough, visit www.howstuffworks.com.

Quick Yeast 

The easiest yeast to use is Quick Yeast, which is a fine granulated powder that can be mixed straight into the flour. Use 3 teaspoon of quick yeast to 1.5kg of flour.

Fresh Yeast

Compressed cakes of crumbly fresh yeast will keep for about two weeks in a refrigerator. Discard fresh yeast if it has gone brown and hard. To activate fresh yeast it is creamed into a sugar and water solution at about 35ºC (95ºF). After 15-20 minutes the mixture will be frothy and ready to add to your flour. Use 50g (2oz) fresh yeast for 1.5kg of flour.

Dried Active Yeast

Is a dehydrated form of compressed yeast with the appearance of small 1.22mm spherical granules. It has a long shelf life, provided it is kept airtight. It is activated in the same way as fresh yeast by whisking into a sugar and water solution at about 43ºc (110ºF). The mixture will be frothy and ready to use after 15 minutes. Use 1oz (25g) dried active yeast for 1.5kg of flour.

Baking Powder

It is the chemical combination of an acid and an alkali in baking powder that produces carbon dioxide gas which can raise baked goods. Commercial baking powders sometimes contain an inert filler such as wheat or rice starch so check the ingredients label if you are on a special diet or make your own baking powder.

Historically baking powder is a nineteenth century invention. A famous chemist, Justus Von Liebig, explored the relationships of organic chemistry to agriculture and plant physiology. He was interested in obtaining maximum plant yield and to control processing of grain without wastage. Instead of using yeast he tried to raise bread with sodium bicarbonate and hydrochloric acid, with uncontrollable, dramatic and sometimes explosive results.

He eventually found the combination of sodium bicarbonate and monoclacium phosphate, when mixed with water, would release carbon dioxide at a controlled rate for successful baking. This is still the basic formula for many modern baking powders.

Self Raising Flour

The correct proportions of the raising agents, acid and alkali, are already added into self raising flour. The raising agents used at Doves Farm are sodium bicarbonate and monoclacium phosphate.

Sodium Bicarbonate (E300)

Sodium Bicarbonate, sometimes called Bicarbonate of Soda, is an alkali and can be used on its own as a raising agent if the dough or batter is sufficiently acidic to allow a reaction that creates carbon dioxide. Lemon juice, yoghurt molasses and sour cream are acidic enough to react with Sodium Bicarbonate but may impart a distinctive strong taste to your baking.

Cream of Tarter (Tartaric Acid E334)

Cream of tartar is a fast acting acid that can be combined with bicarbonate of soda to make your own raising agent.

Ammonium Bicarbonate (E503)

This alkali is sometimes know as 'vol' because it disappears during baking. It is often one of the raising agents used in biscuit manufacture where the carbon dioxide and ammonia combine to raise the biscuit dough. As a processing aid the law does not require ammonium bicarbonate to be declared on the ingredient label, however we will always tell you if we add it to a Doves Farm product.

Make your own Baking Powder & Self-Raising Flour

Place 3 teaspoons of bicarbonate of soda with 4 teaspoons of cream of tartar in a jam jar and shake well. Use as required where a recipe call for baking powder.

To make self-raising flour, add 1tsp of baking power to 200g / 8oz plain flour.

Use gluten free flour to produce gluten free self raising – this is suitable to yeast-free diets

Yeast, Gluten and Carbon Dioxide
Yeast is a single-cell fungus that breaks down the starches in wheat flour, forming sugar. This is fermentation. When the yeast works on the starch and sugar molecules, it gives off carbon dioxide gas and alcohol. Yeast is a leavening agent for bread. It is what makes the bread rise.

Flour comes from any kind of ground grain, but most bread contains wheat flour. Two proteins found in wheat flour, gliadin and glutenin, form a stretchy substance called gluten. When you knead dough, you help gluten form long, threadlike chains. These gluten chains help hold the carbon dioxide gas in, creating those tiny holes that create the airy texture of bread.

The big difference between sourdough bread and the "normal" bread you buy or bake today is the source of the yeast. Most bakers today use cultivated yeast that comes in a package. The package contains live yeast fungi in suspended animation! The yeast has been dried, preserved and formed into a powder. You add flour, water, sugar and salt to the yeast to make a loaf of bread. The water re-activates the yeast fungi, which feeds on the sugar and starch to make the bread rise.

Sourdough bread deals with yeast in a completely different way. Sourdough yeast fungi are actually kept alive constantly in a liquid medium called a starter. The baker either captures wild yeast that floats in the air to create starter from scratch or gets a cup of active starter from a friend and expands it.

Catching the Wild Yeast
Hundreds of years ago, before there was packaged yeast, bakers used sourdough starter to keep a supply of yeast alive and handy. They kept a pot of live culture in a flour/water medium, and "fed" it daily or weekly so that the yeast remained alive and active. To understand how sourdough starter works, let's look at how you can create a batch of starter using live yeast that is floating in the air!

To perform this experiment you will need:

·   A pottery crock, plastic container or glass jar, preferably with a loose-fitting lid

·   A wooden spoon

·   A piece of cloth

·   Some flour (preferably without any preservatives in it) and water

To start a culture, mix two cups of flour and two cups of water in a glass or pottery bowl (in the old days, a baker probably had a special clay crock for starter). Lay a cloth over the top and let it sit on the kitchen counter. It turns out that there is yeast floating in the air all around us all the time, and some of this yeast will make its way to your flour/water mixture. It will then start growing and dividing.

After 24 hours, you pour off about a cup of the mixture and feed it with another cup of flour and another cup of water. In a few days, the mixture will become frothy as the yeast population grows. The froth is caused by the carbon dioxide that the yeast is generating. The starter will also have a bacteria, lactobacilli, in it. This lends to the slightly acidic flavor of the bread by creating lactic acid! The alcohol that the yeast creates and the lactic acid together are the source of sourdough bread's unique flavor!

A common question at this point is, "why doesn't the flour get infested with all sorts of mold and bacteria and become a disgusting health hazard????" For example, if you put a bowl of sugar water or orange juice out on the counter, that is exactly what would happen. It turns out that the starch in bread flour is something that not a lot of bacteria can easily handle, while sugar is (see How Food Works for some details). Yeast, on the other hand, creates special enzymes to deal with starch. The yeast and lactobacilli also "poison" the culture with the alcohol and lactic acid they produce, and that keeps other bacteria out.

Leave the starter on the kitchen counter for five days. As the starter ferments, it will develop a strong aroma -- bready and alcoholy and not particular appetizing. Feed it every day or two by dividing it in half and adding a cup of flour and a cup of water to one half of it (you can throw the other half away). When you see a watery substance floating to the top, stir it. Sourdough bakers call this "hooch." Over the week the starter became a thick liquid, like pancake batter. It will be slightly yellowish.

At this point you can do one of two things:

·   You can store it in the refrigerator to slow down the yeast. Then you will only have to feed it every 5 or 6 days.

·   Or keep it on the counter and feed it every day.

·   If you don't like the "wild yeast floating in the air" idea, there are other ways to start a starter:

·   Get a cup of starter from a friend or another baker. You take a cup of the starter and add flour and water to make more of it. The starter can go on for years.

·   You can make a starter with normal packaged yeast you buy at the store. Start the same way as described above and simply add a package of yeast to it.

·   Or you can buy a packaged sourdough starter mix at the grocery store or by mail-order.

Some starters use milk instead of water, and some starter recipes call for sugar or honey, which boosts the fermentation. There are starters that use potatoes, too. Potatoes have starch in them, and that supplies more sugar for the yeast to feast on.

When it comes time to bake bread, you add a cup of this live culture to the dough to provide the yeast needed to leaven the bread. You replenish the pot by adding back an equal amount of flour and water, and regular feeding keeps the culture alive.

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