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Quotes - Engineering - SalesEgg products
Pasteurizing egg without cooking it
Liquid egg is the narrowest pasteurization window in food processing. Whole egg is held at about 140°F for a few minutes to meet the regulatory standard; the proteins in the white begin to set only a few degrees above that, and yolk thickens from about 150°F. Egg white is pasteurized cooler still, around 134°F, because its proteins are the most heat-sensitive of the three. There is no room to run the heating medium hot and let the product catch up. The wall the egg touches has to stay within a handful of degrees of the egg, or a skin of cooked protein forms on it in the first hour and the run is over.
That is why liquid egg runs on tubular exchangers with a close-approach hot-water loop rather than on steam, and why the heater is long for its duty. The second feature of the duty is cleaning. Egg protein that has touched a warm wall is one of the harder soils to remove, so these lines run a caustic CIP every production day, often twice, followed by an acid step and a chlorinated sanitizer. The sanitizer and the salted yolk blends, not the egg, are what put chloride on the stainless, and they are the reason the product tube is 316L.
Viscosity, inclusions and shear round out the picture: yolk is thick, whole egg foams, and none of it likes a restriction.
Egg product tubes are 316L at 32 µin Ra, chosen for the chlorinated sanitizer and the salted and sugared yolk blends, not for the egg itself, which is nearly neutral. Grade limits are set out on Material & Construction.
Four degrees between pasteurized and scrambled
Whole egg is pasteurized near 140°F and begins to set not far above it, so the heating water runs only a few degrees warmer than the product, the 316L tube is corrugated to keep the film thin, and the heater is sized long rather than hot.
What liquid egg does in an exchanger
Whole egg has the viscosity of a light cream and foams easily, so air entrainment at the balance tank and the pump is controlled before the exchanger. Yolk is several times thicker and is often sold as a 10% salted or 10% sugared blend for the baking and mayonnaise trades; the salted blend carries about 60,000 ppm chloride and is the one product on an egg line that tests the stainless. Egg white is thin, foams more than whole egg, and sets at the lowest temperature.
Fouling is protein denaturation at the wall. It starts within a few degrees of the pasteurization temperature itself, which is why the margin between the water and the product is held so small, and it accelerates sharply if the flow is interrupted with the heat on. A line that stops for ten minutes with hot water still circulating in the annulus restarts with a cooked film in the heater and often does not recover without a mid-shift clean.
The 316L design for it
The product tube is corrugated 316L, 1 to 2 in. bore, 32 µin Ra inside, with orbital welds at the ends and tri-clamp connections throughout. The corrugation matters more here than on most duties: it keeps the egg film at the wall thin and moving at the low velocities the product tolerates, which is what lets a close-approach design reach pasteurization temperature in a reasonable length. The unit is laid out to drain completely, because egg left standing in a tube between CIP cycles is the start of the next fouling problem.
The annulus carries hot water on a closed loop with the inlet set a few degrees above the product outlet, in 304L since no product touches it; a steam-heated annulus is not offered on egg. Regeneration between raw and pasteurized egg recovers a large share of the heating duty and is built with the pasteurized side at the higher pressure. The cooler takes the egg from 140°F down to about 40°F on chilled water or glycol, where the only concern is viscosity at the cold wall.
What to send for an egg pasteurizer
The product type is nearly everything on this duty, because it fixes the pasteurization temperature, the set temperature and the viscosity in one word. The plant's water and sanitizer settle the rest.
- Product: whole egg, yolk, white, or a salted or sugared blend, with the percentage
- Flow rate, inlet temperature from the balance tank and the required hold at temperature
- Hot water loop temperature control available, or whether we should supply the loop
- Chilled water or glycol temperature for the cooler
- CIP routine, sanitizer type and frequency, and the chloride in the plant water
- Required finish and documentation for the product-contact surfaces
Call and talk it through with an engineer: 1-805-484-2992
Questions on egg pasteurization
Because the driving force is tiny on purpose. With the hot water only a few degrees above the egg, the log mean temperature difference is a fraction of what a steam-heated unit would have, and the surface grows in proportion. A unit sized on a larger difference would be shorter and would cook a protein film onto the wall in its first hour. Length is the price of pasteurizing egg without setting it.
Usually not in normal service, provided the line is drained and rinsed before any stop. At 10% salt it carries about 60,000 ppm chloride, far beyond the figure usually quoted for 316L in neutral water, but it is pasteurized near 146°F for a few minutes at a time on a surface cleaned daily, and the yolk is a buffered, near-neutral product; in that service 316L has a generaly good record. What it will not tolerate is salted yolk left standing in the tube over a weekend.
Yes, as long as the hot water loop is controlled to each product's temperature rather than to a single setpoint, and the flow rate is adjusted for the thinner white so that the hold time is met. Egg white foams more and sets lower, so the loop runs cooler and the balance tank is managed to keep air out. A unit designed for yolk is longer than either needs, and the extra surface does no harm.
The egg in the heater, no longer moving, reaches the water temperature within a minute and sets on the wall. The restart shows as a rising pressure drop and a falling outlet temperature, and the usual outcome is an unscheduled caustic wash. The protection is a control interlock that drops the hot water loop temperature or diverts it the moment the product pump stops, which we specify on every egg heater.
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