Preparing the masa (dough)
- 1 The first major process in tortilla chip manufacturing is the production of coarse masa or dough. In a typical mixture, 2.5 to 3.0 liters of water, 1 kilogram of 12 percent moist com, and 0.01 kilogram of food-grade lime (usually quicklime or hydrated lime) are
added together in a large industrial cooker. The lime is used primarily as an aid in removing the pericarp (hull or skin) during cooking and steeping. The lime also helps to increase the product shelf life by controlling microbial activity, and it affects the flavor, aroma, color, and nutritional value of the chips.
- 2 This mixture is then batch-cooked in either a Hamilton steam kettle or a vertical closed cooker. The Hamilton kettle is indirectly heated by steam, and the grain contents are mechanically agitated. It is designed for cooking at or near the boiling point of the lime-water-corn solution. An elaborate agitation system ensures the uniform transfer of heat by condensing steam through the kettle wall and into the limewater-corn solution. The capacity of these steam-jacketed kettles ranges from 300 to 595 pounds (136 to 270 kilograms). The vertical closed cooker uses direct steam injection to heat and agitate the lime-water-corn solution in a large tank, which serves for both cooking and steeping. Additional agitation is accomplished with compressed air. Because this system is designed for cooking at temperatures well below the solution boiling point (185 degrees Fahrenheit or 85 degrees Celsius), the cooking time is longer than in the Hamilton steam kettles. The capacity of the vertical cookers ranges from 3,000 to 6,000 pounds (1,360 to 2,730 kilograms). Cooking time can vary greatly from a few minutes to a half hour, depending upon which system is used. In general, temperatures above 155 degrees Fahrenheit (68 degrees Celsius) are considered to be the optimum cooking temperatures. Cooking depends on the characteristics of the corn and the interaction of time, temperature, lime concentration, cooking vessel size, and agitation. Nixtamal used for fried products is generally cooked less than nixtamal used for table tortillas.
- 3 Immediately after cooking, the solution is quenched (rapidly cooled) to about 154 to 162 degrees Fahrenheit (68-72 degrees Celsius). This lower temperature decreases water absorption during the steeping process and the cooking time of the nixtamal. The result is a more consistent masa, which absorbs less oil during frying.
- 4 The grain is then steeped for 8 to 16 hours in the cooking vat (if a vertical cooker was used) or transferred to a holding vat (if a Hamilton steam kettle was used). The steeping process allows water to be absorbed, which helps to disintegrate the hull and soften the kernel. During the steeping process, the temperature is dropped to 104 degrees Fahrenheit (40 degrees Celsius).
- 5 After steeping, the solution is pumped into the washers. The cooking liquor is drained off, and the resulting nixtamal is washed with pressurized water or spraying systems. Most of the pericarp and excess lime is removed during this step. Washing in commercial processes is done in two types of equipment: the drum washer and the “lowboy” system. A drum washer consists of a conveyor that transports the nixtamal into a rotating perforated cylinder with internal flights and water sprayers located within the drum. After spraying, the nixtamal passes into a drain conveyor, where the excess water is removed. The lowboy system consists of a receptacle equipped with internal screens and sprayers. The washed nixtamal is continuously removed from the bottom of the receptacle by an inclined belt conveyor food should taste good tortilla chips
. In both systems, a conveyor transports the washed, drained nixtamal into a hopper, which then feeds the stone grinder. The end result, using the typical corn and lime mixture, will be 54 ounces (1.53 kilograms) of 47 percent moist nixtamal.