All About Leavening
from http://www.insidethejewishbakery.com/

Put Simply, leavening is the difference between a brick and a bread, cake, or pastry (cookies are a different story entirely). By way of background, the word itself comes from the Latin libero, which means "to raise," and is the ancestor of words like levain and levadura (French and Spanish respectively for leavening), "levitate," "alleviate," "lift," "libation" (raise the cup) and "liberty." Which makes perfect sense when you consider that leavening is both the agent and the process that elevates (also a libero descendant) the dough.

Although there nominally are three ways to leaven baked goods, all depend, at the end of the day, on steam, which at its standard boiling point of 212°F/100°C expands to almost 1,700 times the volume of the water that produced it.

Two of the three methods - microbial and chemical - use leavening ingredients that generate CO2 and form bubbles in the dough or batter. Mechanical leavening, on the other hand, is based on either incorporating a great deal of air into a batter, as in classic sponge and pound cakes; or creating thin, flexible layers of dough, separated by equally thin layers of fat, forming expandable pockets that can capture the steam, as in puff pastry and pie crusts.

In practice, most of the steam generated during baking will escape through broken bubbles and gaps between laminations, but enough will stay in the dough or batter long enough for the heat to set the proteins, hardening them into a light, open textured matrix, even after the product has cooled. For a substance that can, under pressure, pull 100-car freight trains and power entire factories; raising a loaf of bread, croissant or apple turnover is - pardon the expression - a piece of cake.

Steam

The rapid expansion of steam produced during baking leavens the bread, which is as simple as it is unpredictable. The best known steam-leavened bread is the popover. Steam-leavening is unpredictable since the steam is not produced until the bread is baked.

Steam leavening happens regardless of the rising agents (baking soda, yeast, baking powder, sour dough, beaten egg whites, etc.).

The leavening agent either contains air bubbles or generates carbon dioxide.
The heat vaporises the water from the inner surface of the bubbles within the dough.
The steam expands and makes the bread rise.
This is the main factor in the rise of bread once it has been put in the oven. CO2 generation, on its own, is too small to account for the rise. Heat kills bacteria or yeast at an early stage, so the CO2 generation is stopped.

Mechanical Leavening

As noted above, there are two ways of creating the chambers that capture the steam: whipping and folding (lamination).

Whipping is the process of incorporating air into either fat or eggs, and involves one of two techniques:
- Creaming refers to whipping together sugar and a solid fat, like butter or vegetable shortening As the two combine, the fat breaks down and coats the sugar grains, which then dissolve in the fat, producing a hollow bubble of sugar and fat. The eggs and dry ingredients are then quickly folded in, the batter is poured into the appropriate pan, and put into the oven as quickly and gently as possible.
- The sponge method starts by blending the dry ingredients, egg yolks and any liquids into a thick batter, which then is folded into a stiff meringue - a thick, heavily aerated roam of of egg whites, cream of tartar and sugar.
Lamination is a process in which dough and fat are layered together, rolled out, and folded. This process is repeated until there are hundreds of ultra-thin layers of dough, each separated by an equally thin layer of fat. Although this may sound daunting, in fact, it's not particularly complicated.
For example, Danish pastry dough calls for a sandwich of two layers of fat between three layers of dough. This is then rolled out and folded into thirds, yielding 9 layers, and then into fourths, for 36 layers. After a chilling, the process is repeated, rolling the dough thin, folding it in thirds, yielding 36x3=108 layers, and then into fourths, for a total of 432 layers. If you're feeling really ambitious, one more three-fold will produce almost 1,300 layers.

If done properly, the process of chilling, folding and rolling not only distributes the fat through the dough, but also encourages gluten formation, making the dough both flexible and elastic, so that it will literally inflate when steam is released during baking.

Microbial (Biological) Leavening - Yeast

Microbial leavening refers to the activity of a single-celled fungus - yeast - that lives all around us. Yeast spends its days and nights eating sugar and excreting CO2 and alcohol, a process documented at least as far back as the breweries of ancient Egypt.

Indeed, for most of recorded history, bakers relied on the foam skimmed from the brewers' vats to leaven their breads; or they propagated the wild yeasts that live on whole grains and some fruites into starters around which they'd build their doughs.

It's hard to say exactly when commercial yeast first appeared on the scene. No doubt the brewers and bakers who parted with their leavens did so for cash in hand. While most of the breads of Jewish Eastern Europe were rye-based and, therefore, relied mainly on wild yeast sourdoughs, the local rabbi often held a monopoly, granted by the community as part of his livelihood, on the yeast needed for baking sweet Shabbes challah, a challah made with 12 strands of bread representing the 12 tribes of Israel.

On the most basic level, all that yeast, eating all that sugar, produces CO2, which in turn creates millions of tiny gluten balloons in the dough that inflate with steam during baking.

However, the actual chemistry of microbial leavening is somewhat more complicated than just yeast at lunch. Fermenting dough supports a host of other microbes and enzymes - many present in the flour itself or in additives like barley malt - that break down complex starch molecules into simple sugars that in turn affects the action of the yeast. They can also produce acids and other substances that give a properly made loaf of bread its ineffable flavor and aroma.

Interestingly enough, although yeast thrives on sugar, too much sugar will actually slow its action considerably. For that reason, most sweet yeast doughs contain high percentages of yeast. Where a typical bread formula may call for 2% fresh yeast as a percentage of total flour, a super-rich dough like babka dough not only calls for 10% yeast, it also boosts the yeast further by combining the yeast, water and part of the flour into a sponge that is allowed to ferment for 30-60 minutes before adding the sugar and fat.

To address this problem, Lesaffre, a leading yeast manufacturer, developed an "osmotolerant" yeast designed for sugar and fat concentrations in excess of 10% of total flour weight, which it markets as SAF Gold Label Instant Yeast.

Yeast is commercially available to home bakers in three forms:

Fresh compressed yeast, also called cake yeast, is made up of living yeast cells and growing medium, usually barley malt and wheat flour, compressed into a crumbly, slightly moist light tan cake. Compressed yeast has the highest concentration of live yeast cells per ounce/gram, but is highly perishable, with a shelf life of about two months, under refrigeration. Before the advent of dry yeast, fresh yeast was the only thing available to home bakers. However, it has since largely disappeared from the shelves of grocery stores. To use cake yeast, simply crumble it into your other ingredients or dissolve it in water.
Active dry yeast, which Fleischmann's developed for the U.S. Army during World War 2, consists of small cylindrical particles of active yeast cells surrounded by a hard shell of dead cells. Although less efficient than cake yeast, active dry's long shelf life - it remains usable for as much as five years - and greater temperature tolerance fueled explosive commercial growth in the second half of the 20th century. Active dry is the most widely available form of baker's yeast, and is available at most supermarkets in ¼oz/7g envelopes and 4oz/114g jars, and in 2-lb/908g packages at warehouse stores like Sam's Club and Costco, as well as on the Internet. To use active dry yeast, most authorities recommend rehydrating it first in hot (105-120°F/40-50°C) water, to which a small amount of sugar or honey has been added.
Instant yeast was developed by Lesaffre - manufacturer of SAF and Red Star yeasts - in the 1980s, and has revolutionized the commercial yeast market. Like active dry yeast, it comes in dry powdered form and has a shelf life of several years; however, it contains a far higher percentage of live yeast cells than active dry, and can be added directly to a dough, without having to rehydrate. Because high-sugar and high-fat doughs can inhibit yeast activity, SAF offers both regular (Red Label) and osmotolerant (Gold Label) yeast for use in pastry doughs. Instant yeast is available in most U.S. supermarkets in ¼oz/7g envelopes, and in 1-lb/454g packages via mail order on the Internet. It should also be noted that some brands of instant yeast, often identified as rapid-rise or bread-machine yeast, contain added ascorbic acid (Vitamin C), a naturally occurring dough conditioner that promotes gluten formation and stimulates yeast activity. While this may be a time-saver, it also cuts down the amount of time that enzymes and bacteria have to unlock the deeper flavor of the dough.

Yeast Conversion Factors

To find weight equivalents among fresh, active dry and instant yeast, multiply by the factors in the table below:

From / To	Fresh	Active Dry	Instant
Fresh		0.50	0.40
Active Dry	2.00		0.80
Instant	2.50	1.25

Chemical Leavening

Chemical leavening is based on one simple bit of chemistry: that an acid like vinegar, buttermilk, or cream of tartar, combined with an alkaline compound like lye or baking soda, produces CO2, which in turn creates the bubbles in a dough or batter that inflate with steam during baking, thereby leavening the bread, pastry or cake.

In the late 1700’s and early 1800's people started experimenting with different ingredients, and found several home made mixtures they could use to help their baked goods raise quickly. They found that they could mix sour milk (clabber) with other ingredients to make bubbles in their batter or dough. They would also mix pearlash (potash) with sour milk (clabbered milk) to get the same effect. Because of this new kind of leavening from a chemical reaction, the dough did not need to sit for a long time before it was baked. It could go from bowl to oven in no time. These types of baked goods are now known as “quick breads.”

In the mid 1800’s it was discovered that cakes and biscuits (quick breads) could be made with a mixture of cream of tartar (acid ingredient) and baking soda (alkaline). Cream of tartar is a by-product resulting from the manufacture of grape wine.

In 1854, baking powder was invented, using acid phosphate instead of cream of tartar. The leavening reaction between the phosphate and baking powder was controlled, resulting in a dependable leavening action. Foods came out light, flakey and tasty, without any bitterness from pearlash and without setting milk out for days to “clabber,” or sour enough to work in a recipe.

The first written reference to chemical leavening appeared in 1796, in American Cookery, by Amelia Simmons - generally regarded as the first American cookbook. In it, the author calls for the addition of pearlash, a mild form of lye derived from wood ashes, to gingerbread dough as a way of lightening the crumb.

News of this American discovery spread quickly across the Atlantic, and by the mid-19th century bakers everywhere were leavening cakes and pastries with some combination of acid and alkaline.

Chemical leavening really didn't figure prominently in traditional Jewish baking, but only entered the baker's repertoire late in the 19th century, when the pastries and cakes of cities like Vienna, Berlin, Budapest, and Warsaw began filtering back to the shtetls; and more importantly, in America, where improving economic conditions, availability of ingredients and the vigorous cultural ferment of the Melting Pot created a demand for products that, for most Jewish immigrants, were near-mythic, if not totally unknown, back home.

Early Chemical Leaveners

Salt of hartshorn (Ammonium Carbonate). Hartshorn is one of the oldest of "chemical" leavens. It was actually in use for many centuries before the predecessor of modern baking powder was developed in the middle of the nineteenth century. A dough that contains hartshorn produces a strong smell of ammonia when it's in the oven, but the ammonia dissipates completely during the cooking process leaving no aftertaste or odor. Its unique action makes extremely crisp cookies and crackers.

The original hartshorn, as its name implies, was ground from deer antler and used primarily in Scandinavian countries. Today it is almost unknown although there is a chemical version of the original, better known as "baker's ammonia," available from King Arthur Flour – The Baker's Catalogue.
Pearlash (potassium Carbonate). On this side of the Atlantic the early colonists were blessed with hardwood forests as far as the eye could see. Aside from being a logical building material and fuel, hardwoods provided another important resource, ashes. Ashes were a major export two hundred years ago, both to Canada and Britain. They were valuable for sweetening gardens and providing lye for making soap. They were also a source of potash and its derivative, pearlash, another creative leavening agent.

To make pearlash, you first have to make potash which itself is made from lye. To make lye, you pass water through a barrel of hardwood ashes over and over until an egg can float on the residue. (To make soap you boil this "lye water" with lard or other fat until it is thick, pour it into molds and harden it into cakes.) To make potash, you evaporate lye water until you have a solid.

Pearlash is a purified version of potash. It is an alkaline compound which will react with an acidic ingredient such as sour milk, buttermilk or molasses to produce carbon dioxide bubbles, the very same thing that yeast produces. Pearlash was used primarily in the seventeenth and eighteenth centuries but because of its bitter aftertaste, it not only did not replace yeast but was eventually replaced by "saleratus."
Saleratus (Potassium Bicarbonate or Sodium Bicarbonate). Saleratus was originally potassium bicarbonate, and began to replace the pearlash in cookbooks in the early 1850's. As sodium bicarbonate (soda) became more common and the use of potassium bicarbonate was discontinued, a few people continued to call soda 'saleratus.' Like pearlash, potassium bicarbonate had an unpleasant aftertaste and fell out of use early in the nineteenth century. So "saleratus" came to mean just sodium bicarbonate (bicarbonate of soda) itself. You'll find it in nineteenth century recipe books used just as baking soda is used today.

Saleratus was first sold on this side of the Atlantic by John Dwight, who, with his brother-in-law, Dr. Austin Church, started manufacturing it in their kitchens. It was called "Dwight's Saleratus" with a cow as a trademark because of the necessity of using sour milk to activate it in baking. The descendants of Austin Church and John Dwight formed Church & Dwight, Co., introducing their old saleratus as Arm & Hammer Baking Soda. Today that company produces almost all the baking soda that is used in this country.

From Linda Trent, article for the Citizens' Companion (American Civil War civilian magazine) on the Rise of Chemical Leavening in the 19th century. [April/May 1997 issue]

I used 13 cookbooks published between 1796 and 1861 and a cookbook from 1880 and one from 1884. My findings were that prior to the 1830s pearlash was most frequently found only in gingerbread, but by 1833 it was found in numerous other receipts as well.

Saleratus began to replace the use of pearlash by the early 1850's. Showing 43 receipts in Mrs. Chadwick's ‘Home Cookery’ NY: Crosby, Nichols, and Company, 1853. To Pearlash's 2 receipts.

Soda or sodium bicarbonate showed up minimally prior to 1861, but it was in 1861 that it began to take center stage with 59 receipts calling for its use and another 27 for soda's use with tartar. My 1861 source is a reprint of Mrs. Haskell's ‘The Housekeeper's Encyclopedia...’ NY: D. Appleton and Company, 1861.

Baking powder was just starting to make its appearance in 1880 with 4 receipts from the ‘Buckeye Cookery.’

Later Chemical Leaveners

Baking Ammonia is a mixture of ammonium carbonate, ammonium bicarbonate and ammonium carbamate that decomposes rapidly when heated to form CO2, ammonia gas and water. Because baker's ammonia acts quickly and needs to be thoroughly heated to drive off all of the ammonia gas, it's most often used in small products that are baked until dry, such as cream puffs, cookies and egg kichel. Practically impossible to find at retail, baker's ammonia is a specialized product that's used almost exclusively in commercial bakeries.
Cream of Tartar is actually a fancy nom de plume of sorts -- It's the cooking world's name for potassium bitartrate, or potassium hydrogen tartrate, a potassium acid salt that is formed during grape fermentation. Corked wine bottles, fresh grape juice and fresh jams and jellies form crystals, also called "wine diamonds," when stored below 50 degrees Fahrenheit. The wine diamonds sometimes adhere to the sides of the fermented grapes' containers, but can also be found when wine is filtered. The crude form is also called beeswing. The purified form is what we know of as cream of tartar.

Cream of tartar has a number of culinary uses. Many chefs add about 1/8 teaspoon of cream of tartar per egg when beating whites to make meringue―this keeps them stable and adds volume. It also prevents sugar from crystallizing, so mix in a small amount to create smooth icings, syrups, and caramels. Cream of tartar is also a common ingredient in baking powder. If in a pinch, make your own baking powder by combining two parts cream of tartar with one part each baking soda and cornstarch (when dissolved in water, cream of tartar becomes acidic and activates the baking soda, causing baked goods to rise).

The modern process for manufacturing Cream of Tartar was developed by the Swedish chemist CW Scheele in 1769. Later the properties of Cream of Tartar was discovered by Jean Baptiste Biot in 1832. The item gained most of its popularity when the French began using it frequently in their cooking.

Cream of Tartar is the byproduct of the wine industry. When tartaric acid is partially neutralized with potassium hydroxide, potassium bitartrate salt or Cream of Tartar is formed. Potassium bitartrate crystallizes on the walls of the wine barrels. The crude form also known as beeswing are scrapped off from the walls of the barrels. The scrapped wet tartrate is then dried open and later allowed to be baked in a hot blazing furnace at very high temperatures (800-900 degree Celsius). After the completion of heating process, the hardened sediments are then purified and grounded to obtain a white powder. One portion of the powder is mixed with sulphuric acid whereas the other half is mixed with carbonate soda. Both the mixtures are blended together and this process produces the colorless powder of Cream of Tartar. Carbon block is used to remove odor of wine from the Cream of Tartar.
Baking Powder, which was invented by British pharmacist Alfred Bird, appeared in 1843. Half a century later, a German pharmacist, August Oetker, developed and aggressively marketed a baking powder named Backin that's still sold today. (Incidentally, both Bird's and Dr. Oetker flourished over the years and have become leading European consumer packaged goods brands.

Baking powder can be either single- or double-acting.
- Single-acting baking powder, which contains only acid and alkaline, reacts in the presence of water, and even without it; heat is not necessary to get it going. Thereform, it's critical that batters made with single-acting get into the oven before the fizz dies off.
  
  The next logical step after developing baking soda (which only worked when there was something acidic in a batter) was to create a "combination" powder which just needed to get wet to become active. To do this, baking soda was combined with a powdered acid along with a little cornstarch to keep the two dry and inactive. This second magic powder was "cream of tartar," a fruit acid that accumulates on the inside of wine casks as a wine matures. When baking soda and cream of tartar are moistened in a batter or dough, they begin to react to each other right away producing (you guessed it) lots of carbon dioxide bubbles. This combination powder is still a very effective leaven although it has a couple of drawbacks.
  
  As its name indicates, it is "single acting." When it's mixed into a batter or dough, it starts and finishes its reaction then and there. When you bake with it, you must get whatever you're making into a preheated oven as quickly as possible before the bubbles begin to disappear. The second drawback is that, no matter how dry these combination powders are kept, they lose their potency after awhile. In spite of these limitations, there are people who still prefer the flavor of this old blend and value the fact that it is composed entirely of naturally occurring ingredients.
- Double-acting baking powder, on the other hand, contains both the acid-alkaline combination of its single-acting cousin, plus a second slow-acting acid that only activates when heated. This gives batters made with double-acting baking powder a more forgiving nature and what the bakers call a longer bench life. This is the leaven that our recipes are written for unless something else is specified.
  
  Double acting baking powder is single acting backing powder taken one step further. The baking soda is still there but the cream of tartar has been replaced by two acids, one like cream of tartar that reacts to the baking soda as soon as it's wet, the other that doesn't begin to react until it's heated. This means you can be more leisurely about getting a dough or batter into the oven. The acid you find most frequently in double acting baking powder are calcium acid phosphate and sodium aluminum sulfate.
  
  Like single acting baking power, double acting baking powder contains a little cornstarch to prevent the soda and acids from reacting. And it too will lose its leavening ability after a while. If you want to see if it still has its "get-up-and-go," put a little in a cup of hot water. It should start fizzing and bubbling right away.
Baking Soda, also known as bicarbonate of soda and sodium bicarbonate, is an alkaline compound that reacts with acid to produce CO2. Unlike baking powder, baking soda doesn't contain any acid, so its leavening action depends on other acidic ingredients in the batter, such as buttermilk, chocolate, natural cocoa, fruit juice, honey, molasses and sour cream. Baking powder does not need an acidic ingredient to release its leavening power.

Baking soda comes from several sources, but the bulk of it is derived from an ore called "trona" which is mined in the Green River Basin in Wyoming. (Technology is being developed now to produce baking soda from sea water.) When baking soda is heated, it slowly breaks down into sodium carbonate, water and those magic leavening bubbles, carbon dioxide. When mixed with something acidic and wet, it starts producing carbon dioxide right away without waiting to be heated.

Homemade Baking Powder (single acting baking powder)

Since baking powder does tend to lose its leavening powder after a while, rather than being caught empty handed, it's useful to have baking soda and cream of tartar around in separate containers. Then you can make your own baking powder in an emergency. These are both available separately at your grocery and, separated, have an indefinite shelf life.

To make the equivalent of 1 teaspoon of baking powder, mix 1/2 teaspoon of cream of tartar with 1/4 teaspoon baking soda (two parts of cream of tartar to one of baking soda). This single acting baking powder will work very successfully but you must remember that when you use it, get whatever you're baking into the oven right away.

When & How To Use Baking Powder

First count the cups of flour your recipe calls for. You want to include at least 1 teaspoon of baking powder per cup. If your recipe contains a cup or more of decorative ingredients, add another 1/2 teaspoon of baking powder per cup of flour.

Example: Let's say your recipe calls for 3 cups of flour and 1 cup of raisins. First you'll need 1 teaspoon of baking powder for each cup of flour. That makes 3 teaspoons. To help lift those raisins, you'll want an extra 1/2 teaspoon of baking powder per cup of flour. This makes 1 1/2 teaspoons or 4 1/2 teaspoons of baking powder altogether.

When & How To Use Baking Soda

Baking soda is used generally when there is an ingredient in a batter that is particularly acidic, such as buttermilk or molasses, anything that can take the place of the acid in the baking powder.

Example: If our recipe contains 3 cups of flour plus 1 cup of raisins and we want to use 1 cup of sweet milk, we blend 4 1/2 teaspoons of baking powder into the flour. If we want to substitute 1 cup of buttermilk for the sweet milk, we'll blend 1/2 teaspoon of baking soda into the flour and use only 2 1/2 teaspoons of baking powder. In other words, 1/2 teaspoon of baking soda plus 1 cup of buttermilk (or an equivalent) can replace about 2 teaspoons of baking powder.

There is no situation where you must use baking soda, even when you have an acidic ingredient in your dough or batter. Because baking powder contains both baking soda and an acid, it will create carbon dioxide bubbles even when there's extra acid present, such as the buttermilk.

You can choose to use baking powder completely, If you do, the flavor of the acidic ingredient (buttermilk, etc.) will be slightly more pronounced since there is no baking soda to react with or neutralize it. The texture will also be a bit finer than the coarse or "shaggy" texture that is characteristically caused by the action of baking soda.