Mozzarella Stretcher

Overview

A mozzarella stretcher is a dairy machine that turns acidified cheese curd into the smooth, elastic body of pasta filata cheeses like mozzarella. Hot water softens the curd, and counter-rotating arms knead and pull it until the protein aligns into stretchy fibers. This automated unit runs the full cycle, feeding curd, holding water temperature, stretching, draining whey, and forming the finished product, at 100 to 300 kg per hour.

The machine is built from a Vat Assembly hot-water tank, a Stretching Arms kneading mechanism, a Temperature Control loop, a Curd Feeder, a Molder Interface discharge, a Drainage System for whey, and a Automation controller tying the cycle together.

Vat and heating

The Vat Assembly holds the hot water that softens the curd. A Inner Vat stainless vessel contacts the curd directly, surrounded by a Outer Jacket double wall that circulates heating water at the 50 to 55 °C setpoint. A Heating Element immersion heater of 9 to 15 kW supplies the heat, a Thermostat dual RTD probe reads temperature to within half a degree, and a Pressure Sensor monitors vat water pressure.

Stretching arms

The Stretching Arms do the mechanical work. A Arm Shaft hollow stainless spindle carries Arm Paddles curved blades that fold and pull the curd as they turn. A Gear Drive of two synchronized counter-rotating gear motors, 5 to 15 kW each, runs the arms at 20 to 60 rpm so the curd is worked from both sides at once. A Bearing Housing pillow block supports the shaft at the vat centerline, and a Seal System double mechanical seal with refrigerated barrier fluid keeps hot curd from leaking past the shaft.

Temperature control

Holding the right water temperature is what makes the curd stretch consistently, so the Temperature Control system manages it as a closed loop. A Heating Valve modulates steam or hot-water flow into the jacket, an optional Cooling Loop circulates chilled water for post-stretch cooling, a Thermostatic Mixer three-way valve trims the outlet temperature to within half a degree of setpoint, and a Control Unit PID controller drives the heater duty cycle.

Feeding and forming

The Curd Feeder meters curd into the vat at a controlled rate. A Curd Hopper holds 50 to 200 L above the vat with a vibratory assist, a Dosing Valve gate or rotary valve sets the feed rate, and an optional Feed Screw auger gives positive, consistent dosing.

Once stretched, the curd leaves through the Molder Interface. A Discharge Pump rotary lobe or screw pump conveys the hot curd to a Forming Nozzle heated die that shapes it into balls of 100 to 500 g or into logs, and a Cutoff Blade heated wire or blade separates the formed product into portions.

Drainage and automation

The Drainage System removes whey released during stretching. A Whey Pump rotary lobe pump extracts 10 to 50 L/min of warm whey without damaging the curd, a Flow Meter tracks the discharge volume, and a Drain Line with a check valve carries whey to storage or treatment.

The whole cycle is run by the Automation controller. A Automation PLC industrial PLC sequences the stretch, drain and discharge phases, a Recipe HMI touchscreen stores and selects recipes for temperature, time and arm speed, and Motor Drives variable frequency drives set the two arm motor speeds independently so each recipe gets the right kneading action.