October 1, 2008
by Laurie Gorton
Already a highly automated process, the manufacturing of flour tortillas has gained efficiency, speed and reliability from the application of computer control technologies. Like most other bakery processing technologies, tortilla manufacturing methods benefit from step-wise advances rather than quantum leaps. Over the past few years, heat-press lines moved from intermittent pressing to continuous motion systems, and counter-stackers continue to improve in reliability and accuracy.
One significant change at the supplier level was the merger of Stewart Systems, Plano, TX, into AMF Bakery Systems, Richmond, VA. The joined company formed a tortilla technology division to manage the design, manufacture, sale and service of corn and flour tortilla processing equipment.
THREE MEANS. Wheat flour tortillas are made by three separate methods, each resulting in products with different characteristics and applications. Hand-stretching and pressing result in the most traditional styles favored for table tortillas, while die-cut flour tortillas find use fried as edible salad bowls and in entree preparation for food service and frozen foods.
Pressed tortillas are smooth and slightly shiny in appearance. They tend to be pliable and slightly elastic and can be easily rolled or folded without tearing. Their texture and crumb are light and fluffy, with pronounced layering and flake. Hand-stretched tortillas generally have a dull appearance and dry, powdery feel caused by residual dusting flour from the manufacturing process. They have a tender bite and are dense with little layering or flake. Die-cut tortillas have a dry, powdery feel from the dusting flour and are generally tough, chewy and very dense, with no flake or layers.
Dough for pressed tortillas tends to be under-mixed and is set at 90 to 100°F (32 to 38°C). The higher dough temperatures and under-development help the dough pieces relax more quickly after dividing and rounding, thus facilitating pressing and stretching operations. Flour tortilla dough goes directly from the mixer to the divider, with no floor time, and is very similar to that of hearth bread and roll doughs. It is very stiff and dry.
Dough balls fall from the overhead proofer down chutes into a template that positions them correctly on the belt below. The template head descends to lightly press the dough balls so they don’t roll out of place. The press and the plate under it are heated to 350 to 450°F (177 to 232°C), with a dwell time of 1 to 2 seconds. The press operates at 400 to 1,000 lb per sq in. The exact pressure, time and heat depend on the tortilla’s formulation, hence the ranges noted here.
Flour tortillas bake in a compact 3-tier oven. The tortillas move on a conveyor chain and are, thus, inverted or flipped twice during the baking cycle. A 3-pass oven reflects the home method of placing the dough piece on a hot griddle and flipping it twice. This sets the starch. Oven temperatures range from 375 to 500°F (191 to 260°C), and baking time varies from 25 to 40 seconds. Nearly all of the browning takes place by conduction from the hot (500°F, or 206°C) surface of the oven’s baking plates or mesh bands.
Often, tortillas emerge from the oven puffed up like partially inflated basketballs. The heat of the oven causes leavening gases supplied by yeast and/or chemical agents to expand quickly, and moisture inside the dough flashes into steam. All these gases are held inside the tortilla by the skin created during heated pressing. The gases dissipate quickly, and the tortillas collapse into their normal form.
Flour tortillas are still relatively fragile hot out of the oven and must cool sufficiently for packaging, or they will stick together. A cooling conveyor carries the warm tortillas along multiple tiers for 2 to 5 minutes. Enclosed coolers maintain a temperature of 40°F (4°C) for the air circulating through them; ambient coolers are open to the plant environment and are typically cooled by fans.
Formulation requirements for hand-stretched flour tortillas are generally leaner than for pressed tortillas, with reduced amounts of water, shortening and salt. Mixing time is longer because this tortilla style is sheeted twice during makeup, thus requiring additional gluten development. Again, no floor time is needed, and the dough goes directly to the divider /rounder and into an intermediate proofer. The 2-stage sheeting process first reduces the dough ball into a flat round. The piece is turned 90°, and a second sheeting pass produces a flat ellipse.
Operators stretch the dough piece by hand, turning out a fully circular piece. Stretching takes place over a heated plate that interrupts the conveyor line, and the extra heat helps set the skin of the tortilla. Hand-stretched tortillas bake for a very short time, 17 to 25 seconds, and are conveyed out of the oven onto cooling conveyors.
Die-cut flour tortillas are made on a sheeting line. Dough, extruded in a continuous ribbon onto the line’s conveyor, is sheeted and cross-rolled to achieve a thickness of 0.125 to 0.1875 in. (3 to 5 mm). A cylindrical die roller cuts circular shapes out of the continuous dough sheet, with scrap dough returned to the extruder for reuse. Die cutting is harder on the dough physically than either the pressed or hand-stretched method, so dough conditioner levels in the formula are generally increased. Baking and cooling times are similar to those of pressed and hand-stretched tortillas.
Tortillas should be as close to plant ambient temperature as possible when packaged. Higher temperatures will cause moisture to condense inside the package, encouraging mold growth.
PLC PACED. Today’s flour tortilla lines such as the Mega OP/AL system from Lawrence Equipment, South El Monte, CA, have been steadily increasing in output capacity. This line delivers up to 4,500 doz 6-in. tortillas per hour. KB Systems, Bangor, PA, offers a tortilla line with output at 2,000 doz 6-in. pieces per hour.
Sequencing via programmable logic controller (PLC) is a must for such systems. For example, the Lawrence Equipment line’s One Touch Control system allows the operator full control over all processing variables. For example, when changing the press cycle rate, the controls automatically adjust divider, proofer and cooler speeds. The press transfer belt speed is automatically calculated to ensure that transfer speeds are kept as low as possible, and controls make it impossible to feed pressed tortillas into the oven faster than it can receive them, thus eliminating folds.
The large platens used for tortilla pressing require precise temperature control. To achieve this level of performance, Casa Herrera, Pomona, CA, uses a touch-screen PLC terminal to govern the 18 heaters per platen on the company’s TP-4242 programmable flour tortilla press.
Also benefiting from the speed of PLCs is the inspection function. Casa Herrera recently introduced the CH-51 automated inspection system, developed in association with Sharpvision Group USA. The vision unit is inserted directly into the processing line to examine tortilla size, color, toast points, folds and holes at
up to 12,000 inspections per minute. An automatic air ejection system removes “out of spec” products.
Programmable counter-stackers such as the Genesis system from ARR-Tech, Yakima, WA, and the Counter Stacker CSPS from J.C. Ford, La Habra, CA, offer improved accuracy. Designs accommodate 1,800 to 5,400 doz per hour, counting stacks of four to 60 tortillas each. While the Genesis counter-stacker features a universal product laning air chute system designed for quick changeover, J.C. Ford designed its new stacker with adjustable feed angles and quick change canisters to allow two, three or four row stacking of flour tortillas.
DIVIDING ADVANCES. Rotary dividing is making headway in flour tortilla production. AMF and its Stewart Systems Tortilla Equipment Division recently put this technology to work on the company’s Solstice S3 line. The divider, designed and manufactured in accordance with BISSC sanitation standards, requires no divider oil or dusting flour.
A dual-auger design handles dough gently, and the patented ultra-high molecular weight (UHMW) plastic free-flow manifold evenly distributes dough for 4-, 6-, 8- and 9-across output. Servo motors control the action of the UHMW rotary cut-off mechanism, which operates at 110 to 200 cuts per minute. Divider pressure is set deliberately low at 15 psi to be gen- tle to the dough, and dough temperature varies less than 1° from hopper to discharge, so no cooling is required for the rounding bed, according to the manufacturer.
Tortilla processers who prefer conventional dividing can opt for the Oddy Novatek dividerrounder , available from J.C. Ford and Kaak Group North America, Lithia Springs, GA. This system’s low-stress scaling cylinder gives a weight range of 10 to 500 g (0.3 to 17.5 oz), using change pieces and lane reduction. It requires no divider oil and runs at 50 strokes per minute.
CONTINUOUS ACTION. Until recently, pressing was an intermittent process. The press’ conveyor stopped while dough balls were deposited on it and tapped into place to prevent them from rolling out of position. Then the platen would descend to flatten the balls and then rise out of the way. The belt resumed travel to move the pressed tortillas to the oven. New “flying head” technology from AMF/Stewart uses continuous horizontal and vertical movement of the press to complete more than 20 strokes per minute. An automatic dough detection system allows pressing only when dough balls are present, and the press maintains exact product spacing.
Servos drive J.C. Ford’s new continuous tortilla press. Its capacity ranges from 990 doz per hour for 12-in. tortillas to 2,200 doz per hour for 6-in. tortillas.
ENERGY EFFICIENT. In the past, tortilla ovens had been notorious for wasting energy. To get enough oxygen to the burners, some operators would prop open or completely remove the oven’s insulated panels. There’s no need for that with the new energy-efficient oven designs now available.
For example, the new Solstice S3 tortilla oven from AMF/Stewart is designed to proportionally mix combustion air. Other heating improvements include individual burner controls and pilotless active flame management. The doublewalled microporous insulation has an increased intralayer air gap that functions as a heat sink to cut air loss from the oven chamber and reduce the temperature of the outer walls.
Finally, engineers of flour tortilla equipment are giving more attention to sanitation. Clean-in-place capability is part of many new designs such as Lawrence Equipment’s Legend cooling conveyor. Its washdown design eliminates standing water and debris collection.