Tortilla Tips: Ingredients and pH – Part 2 Equilibrium

To help understand pH and equilibrium imagine two lakes.  The lake on the left is alkaline and the lake on the right is acidic. An underground tunnel or cave connects the two lakes.  If the level in the alkaline lake is higher than the acidic lake, some of the water flows through the cave into the acidic lake. Eventually the levels of the lakes are equal or at equilibrium.  In a similar manner the amounts of the alkaline and acidic ingredients in a tortilla will reach equilibrium , which is the final pH of the product.  The time to reach the final pH, i.e. the size of the tunnel, is determined by the solubility and reaction rates of the acids and bases in the tortilla.  To make great tortillas we need to regulate the amounts and types of alkaline and acidic ingredients.

The impact on pH of common ingredients is indicated in Table 1. The strength of many acidic or alkaline ingredients is known but those ingredients with an asterisk (*) have variable strengths or impacts on pH.

Table 1: Impact on pH of common tortilla ingredients.

Acidic

ascorbic acid benzoic acid citric acid fumaric acid monocalcium phosphate phosphoric acid propionic acid sodium acid pyrophosphate sodium aluminum phosphate sodium aluminum sulfate sorbic acid

Neutral

baking powder* calcium propionate* corn corn starch fats and oils gums* methyl paraben mono-diglycerides potassium sorbate* rice flour salt sodium benzoate* sodium propionate* sugar vital gluten wheat flour yeast

The alkaline compound in flour tortillas is almost always sodium bicarbonate.  All acids react with (neutralize) sodium bicarbonate, form carbon dioxide and lower the pH of the dough.  Acids commonly used in flour tortillas include fumaric acid, citric acid, sodium aluminum sulfate (SAS), sodium acid pyrophosphate (SAPP), sodium aluminum phosphate (SALP), and monocalcium phosphate (MCP).  Acids less commonly used include ascorbic acid, malic acid, adipic acid, sorbic acid, and propionic acid.  Citric acid is soluble in water and reaches an equilibrium pH in the mixer.  This expends most of the sodium bicarbonate in the mixer and little remains for leavening in the oven.  This is undesirable for flour tortillas.  When using acids that are less soluble in water, like SAS or fumaric acid, reaction rate is lower and it may take several hours or days for the tortilla to reach equilibrium pH.

Tortilla Manufacturers often ask how to measure the pH of flour tortillas.  The principal of equilibrium that was just explained is often over looked.  Tortilla Manufacturers who measure the pH of the dough are surprised when the baked tortilla has a different pH.[1] Try measuring the pH at three stages during production:  (1) after the dough is mixed, (2) immediately after the tortilla is baked and cooled, and (3) after 24 hours in a package at room temperature.  Often the pH of the tortilla decreases a small amount (0.1-0.3 pH units) during the first 24 hours after production.  Records of pH for each formula will provide a basis as to when the pH should be measured and their acceptable values. By having these records, production managers will know if the pH of dough is appropriate or what the pH of the tortilla will be in 24 hours.

^a Leavening acids are used to neutralize sodium bicarbonate in chemically leavened baked breads.

^b Sodium bicarbonate encapsulated.

^c SALP = Sodium Aluminum Phosphate.

^d SAS = Sodium Aluminum Sulfate.

^e Sodium bicarbonate regular.

^f Sodium bicarbonate fine.

^g SAPP-28 = Sodium Acid Pyrophosphate with reaction rate of 28.

(C) 2010