Many types of baked goods, e.g., breads, cakes, muffins, pancakes, etc., rise as they cook, i.e., they increase in volume and become more airy. How does this happen? Well it’s not smoke and mirrors, legerdemain, or a little gremlin with an air hose. Actually the gremlin would make for more interesting reading but the truth lies squarely in the cold, hard realm of science. The rising effect is due to a leavener. Leaveners are natural or chemical entities that boost the volume of baked goods. The most common mechanism of action is carbon dioxide (CO2) gas but as we shall see, steam and air can also serve as leaveners. Let’s peruse the various substances that take our foods to new heights.
Yeast is the primordial leavening agent. Yeast is a living organism, more precisely a one-cell plant that feeds on simple sugars and then egests alcohol and carbon dioxide as a byproduct. There are numerous strains of yeasts with different properties and applications but for the purpose of the present discussion we will focus on the main three: fresh yeast, active dry yeast, and instant yeast.
Fresh yeast, also known as compressed or cake yeast, is completely fresh, unadulterated yeast. Many professional bakers consider it the most reliable since it has the greatest dough-raising ability. It is often sold in blocks but sometimes crumbled in bags. The problem with fresh yeast is it is highly perishable. It is not uncommon to find semi-dead blocks of fresh yeast right off the supermarket shelf. Serious bakers seek out reputable baking supply stores with high turnover to ensure pristine specimens. It must be stored in the fridge but even still, its days are seriously numbered.
Because of the fragility of fresh yeast, active dry yeast has become very popular. Active dry yeast is oven dried. It is sold in foil packets often interconnected to produce a two to three pack sleeve. It can last up to a year in the fridge. Be sure to keep an eye on the expiration date because it too will eventually kick the bucket. Dead yeast does not “breathe” and thus will not expel carbon dioxide.
Active dry yeast needs to be “proofed,” i.e., activated in warm water first. This means whisking it into a small bowl of water and allowing it to sit for 5 minutes. But the water must be between 100 and 110 degrees, preferably 105 to 110. Temperatures below and above this margin will prevent the yeast from optimally dispersing CO2. Moreover, water temperatures significantly beyond this range will outright kill the yeast. Employ an instant read thermometer and avoid these perils. Due to the manufacturing procedures about 25% of the yeast cells are killed in the processing of active dry yeast. This renders it the least “riseable” of the different types of yeast. All the more reason to make sure you proof it at the correct temperature.
Instant yeast, also known as quick rise or fast rise, is the test tube baby of yeasts. Genetically engineered from various strains of yeast to cull the best features into one progeny, instant yeast has high leavening ability, becomes active quickly, and is more resistant to deleterious temperature extremes. Instant yeast does not require proofing and can be mixed directly into the dough. When substituting instant yeast for fresh, use 1/3 ounce instant for every ounce of fresh, and when substituting instant for active dry, use ¾ ounce instant for every ounce of active dry.
Next up on our leavening tour are chemical leaveners, namely baking soda and baking powder. Chemical leaveners are most often employed in “quick breads,” i.e., breads that rise rapidly and don’t have the luxury to rest for protracted periods of time while the yeast belches out its CO2. Classic examples include cornbread, biscuits, pancakes, scones, etc.
Baking soda and baking powder also produce CO2. Baking soda, a.k.a., sodium bicarbonate, is an alkali. Left to its own devices baking soda will give off some gas when exposed to heat. But, mix an alkali with an acid and you get a CO2 fizz-fest. Therefore, when baking soda is employed the recipe will usually contain an acidic ingredient, for example the buttermilk in buttermilk biscuits.
Baking powder contains both baking soda, some form of acid, and cornstarch. The cornstarch keeps the alkaline and acidic components dry and separate. Baking powder can be fast-acting, slow-acting or double-acting depending on the types of acids used. Fast-acting dissolves readily in fluid while the slow-acting disseminates at a more gradual rate. Double-acting goes both ways by creating some leavening when first mixed with the fluid and then again in the heat of the oven. Use about 1 teaspoon baking powder per cup of flour but only ¼ teaspoon baking soda per cup of flour. Both baking powder and baking soda will deteriorate with time and thus produce less leavening. Check the dates and chuck the has-beens.
Air and water can also increase the volume of certain baked goods. An angel food cake is light and airy from the air trapped inside the protein matrix of the egg whites. Air is also beaten into butter when creaming it with the sugar to make a cake. Puff pastry “puffs” from the steam released from the butter as it cooks. Steam and air also play a role in popovers or Yorkshire puddings. In sum, there are a number of means by which your baked goods can, shall we say, rise to the occasion.
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