Leavening Agents

Chapter 21

Air

• Air is not the main leavening agent ,but gives many products a “lift”

• Air is the principal leavening agent in meringues and angel food cakes

• These products are based on egg foams (beaten egg whites)

• Protein traps the air bubbles in the foam, creating a light and fluffy texture.

Steam

• All recipes for baked goods include some liquid.

• The water in the liquid produces steam when heated

• The temperature of the oven usually at least 204ºC ( what is that in ºF)

• Baking coagulates the protein, setting the structure

• Making large pockets or whole appear in food

Carbon Dioxide (Co2)

• Two basic methods for creating carbon dioxide:– Using baking soda, baking powder to create

a chemical reaction that yields the gas– Using yeast in a biological process to create

gas

– http://recipes.howstuffworks.com/bread.htm

Baking Soda

• Baking Soda = chemical compound sodium bicarbonate

• Baking soda releases sodium carbonate as well as carbon dioxide when heated

• Sodium carbonate gives food a bad taste and a yellowish color.

• However, baking soda is always used with an acid, which alters the chemical reaction to prevent sodium carbonate from forming

– Some examples of acid are buttermilk, vinegar, lemon juice, molasses, honey, fruits, fruit juices, and cream of tartar.

Baking Powder

• Baking Powder = leavening compound that contain baking soda, dry acids and starch or some other filler.

• The filler in baking powder, usually cornstarch or calcium carbonate, absorbs moisture in the air, which helps prevent a chemical reaction from taking place too soon.

• Baking powder comes in two types:1. Single-acting baking powder = as soon as liquid is added,

carbon dioxide starts to be released– The quick reaction occurs because the acid in baking powder is

soluble in a cold liquid

2. Double-acting baking powder = usually preferred, contains two acids, one that reacts with cold liquid and one that reacts with heat.

– Some carbon dioxide is released as soon as liquid is added, but most is produced as the batter heats in the oven

The Strength of Baking Powder

• http://chemistry.about.com/cs/foodchemistry/f/blbaking.htm?p=1

• By federal law, baking powder must yield at least 12%. of carbon dioxide, most home used are at 14%– To much baking powder will cause the walls of the

flour mixture to stretch too far, break, and collapse.– Too little will mean a compact product

– http://images.google.com/imgres?imgurl=http://static.flickr.com/102/307198454_c1432aab3d.jpg&imgrefurl=http://thewanderingeater.wordpress.com/2006/11/10/the-best-of-croissantspart-2/&h=392&w=500&sz=126&hl=en&start=29&um=1&tbnid=qVDAkULXAM8q2M:&tbnh=102&tbnw=130&prev=/images%3Fq%3Dpicture%2Bof%2Ba%2Bcroissant%26start%3D20%26ndsp%3D20%26svnum%3D10%26um%3D1%26hl%3Den%26rlz%3D1T4RNWN_enUS220US221%26sa%3DN

Ammonium Bicarbonate

• Baking soda and baking powder are the most common chemicals used to produce carbon dioxide, however ammonium bicarbonate can be used.– Ammonium bicarbonate produces carbon

dioxide as it decomposes– Mostly used in crackers and certain types of

cookies because of the affect to taste

Producing Carbon Dioxide (CO2) with Yeast

• Yeast is a microscopic organism that produces carbon dioxide through fermentation = biological reaction that slowly splits complex organic compounds into simpler substances

• During fermentation, yeast converts sugar into ethyl alcohol and carbon dioxide, ethyl alcohol evaporates while the carbon dioxide causes the product to rise

• Yeast is killed in high baking temperatures

The Origins of Yeast

• Thousand of years ago a little yeast landed on some bread dough and started to ferment, making the dough rise.

• Ancient Egyptians first leavened bread by using yeast piece of leftover dough.

– They started getting the same results using beer froth which also contains yeast

– The word “yeast” originally meant the froth or sediment of a fermenting liquid

– In ancient Rome, grape juice was mixed with wheat bran, ferment to develop yeast. The cakes were cut and used for bread later.

– Sourdough bread is made by keeping the yeast alive from one batch of bread in order to start the next one.

• http://video.google.com/videoplay?docid=2261363315131027664&q=yeast&total=1220&start=10&num=10&so=0&type=search&plindex=9

• Picture of yeast dividing (producing CO2)

Batters and Dough

• Pour batters – made with an equal ratio of flour to liquid, usually flour (ex. waffle and pancake)

• Steam is the main leavening agent in pour batters

• Drop batters – mixing about two parts flour to one part liquid

• Make muffins and some cookies, baking powder and steam are both leavening agents

• Soft dough – three parts flour to one part liquid• Needs more mixing to develop gluten, example yeast breads, pizza

crust and baking powder biscuits

• Stiff dough – six to eight times as much flour as liquid• Drier consistency is needed for some products example pie crust• Steam leavens all flour mixtures

Making Yeast Products

• Beside yeast, the basic ingredients these breads are flour, liquids, and salt– Flour – provides the starch as well as the proteins

that produce gluten– Liquid – usually water or milk. Milk is often chosen

for nutritious reasons and also helps bread stay fresh longer

– During baking, the steam from the liquid combines with the carbon dioxide produced by the yeast, which helps the bread expand and rise

– Sugar, fat, and eggs – sugar helps the crust brown, fat makes the bread tender (softer), eggs makes the bread richer in texture and flavor.

Making Quick Breads

• Quick Bread = needs no time to rise. These products are made with a leavening agent other than yeast, usually steam or carbon dioxide that is produce with baking powder or baking soda. Ex. muffins, coffee cakes, biscuits etc.

• All quick breads contain flour, liquid and salt, plus a chemical leavening agent.

• When making quick breads, DO NOT OVERSTIR, this will develop gluten, producing a tough product.

Questions

1. What are the three main leavens in bake goods?

2. How do each of the two natural leavens work?3. What are two methods for producing carbon

dioxide for leavening?4. How does baking soda work as a leavening

agent?5. What would happen if you let out the lemon

juice in a recipe that called for lemon juice and baking soda?

6. Compare single-acting baking powder with double-acting baking powder.

Question Continued

7. How much baking soda is in a recipe that calls for 2 teaspoons of baking powder. How do you know this?

8. Why does the amount of baking powder used in a recipe matter?

9. Describe how yeast produces carbon dioxide for leavening.

10. What is the scientific basis for the ancient Romans’ choice of grape juice and a grain products for growing yeast?

11. Should yeast be refrigerated? Why or why not?12. Why do batters need to be thin when steam is the main

leavening agent?13. Are cakes leavened with only one leavening agent?

Explain