LEAVENING AGENTS

DEFINEDAerates mixture increases volume and lightens itLeavening action may be produced by physical, chemical, or biological meansCommon leavening agents: air, steam, carbon dioxide

AIRIntroduced by sifting dry ingredients, creaming and mixing batters, and incorporating beaten egg whitesAll flour mixtures depend on air, but it is not sufficientCreaming fat and sugar for aeration traps carbon dioxide from chemical leaveningKneading incorporates air in yeast breads – carbon dioxide expands air cellsAir importat for fine, even grain of baked products

STEAMUsed because volume of water increases more than 1600 times as it vaporizes and expandsSteam alone not sufficient-combine with air or carbon dioxideRecipes are liquid batter (popovers)-volume of flour=volume of liquidMust use high temperatures so boiling point reached quickly

CARBON DIOXIDEGenerated by chemical leaveners or produced from sugar by yeast Time of release important: some during mixing so fine bubbles will be dispersedFine dispersion=fine crumb and thin cell wallsEmulsions maintain gas emulsion in batterMajor portion of carbon dioxide released in oven before crumb is set

BAKING SODASodium bicarbonate heated sodium carbonate (washing soda), water, carbon dioxide2NaHCO3Na2CO3 + H20 + CO2

Reaction is slowProduces alkaline salt (disagreeable flavor)

ALKALINE SALTIn excess alkalinity changes flavonoid pigments in flour to yellow colorIncreases browning by Maillard reactionProduct slightly yellow with brown spotsIf sodium combines with fatty acid bitter soapy taste

BAKING SODA + ACIDAvoid problems Produces neutral salt residue + carbonic acidNaHCO3 + Hx NaX + H2CO3

Carbonic acid readily H2O + CO2

Carbonic acid unstable

COMMON ACIDSLactic acid in sour milk, buttermilk, yogurtAconitic acid in molasses and brown sugarGluconic acid in honeyMalic acid in apples and pearsTartaric acid in grapesSuccininc, citrus and benzoic acids in fruits and vegetablesAcetic acid in vinegarUsually: buttermilk, lemon juice, vinegar, molasses

PROPORTIONS1 C Milk – replace 1 T with vinegar or lemon juice = sour milk1 C Milk – add 1 ¾ tsp cream of tartarBaking soda – ½ tsp neutralizes 1 cup fully soured milk½ tsp baking soda needs 1 ¼ tsp cream of tartar for complete reactionReaction takes place ONLY in water

BAKING POWDERMixture of baking soda + acids or acid salts separated by inert fillerFederal Standards – must yield >12% carbon dioxide Inert filler = buffer, standardizes strength of powderAcids and baking soda must ionize

IDEAL BAKING POWDERReleases some carbon dioxide at room temperatureReleases most in earlier part of bakingNo aftertaste

SUBSTITUTE½ teaspoon baking soda equivalent to 2 teaspoons baking powder

CLASSIFICATION OF BAKING POWDERS

ACID CONTENTTartrate powderPhosphate powderCombination powder – sodium aluminum sulfate and monocalcium phosphate

REACTIONSSingle acting – fast, produces CO2 as soon as moistened, acid soluble in cold waterDouble acting – slow, reacts twice: once when moistened and then when heated Contains two acids: SAPP – Phosphate powder reacts to moisture; sodium aluminum powder (SAS) reacts to heat

BIOLOGICAL LEAVENING

YEASTNeeds food, warmth, moistureFermentation – enzymes (zymase) convert sugars to alcohol and carbon dioxideCarbon dioxide retained in gluten structureAlcohol evaporatesCANNOT use lactose for fermentation

BACTERIANeed controlled conditions: temperature, moistureGrow and act on sugar CO2 and hydrogen Occur naturally in cornmeal create a sponge to leaven salt-rising breadSourdough bread