1-805-484-2992
Quotes - Engineering - SalesExtended shelf life, heating side
Between pasteurization and sterilization
ESL heating lands between HTST and UHT on purpose. Milk, creamers, flavored milk and oat, almond or soy drinks go to 250 to 260 F for 2 to 4 seconds, and the result keeps 30 to 90 days refrigerated with a flavor much closer to fresh than a shelf-stable product. The heating side has three parts: a regenerative preheat, a preheat hold, and a final heater, and the final heater decides the run length.
This page covers the heating train alone. The cooling train, with its own sterility and pressure questions, is on ESL Cooling.
The heating train, section by section
Preheat and the preheat hold
The first section is regenerative: raw product at 40 F against product returning from the hold, lifting the raw side to 195 to 205 F. Then the product sits in a sloped coil for 30 to 90 seconds. Beta-lactoglobulin denatures fastest between 165 and 205 F; if it does that in the bulk during the hold it complexes with casein and stays in suspension, and if it does it on a 250 F wall it sticks. Lines with a preheat hold run three to four times longer, and the coil is cheap.
Plant-based drinks change the recipe. Oat carries starch that gels above 180 F; almond and soy carry protein that behaves like whey. The hold still helps, but the heater bore is larger and the velocity higher.
The final heater
From 200 F to 255 F is a 55 degree lift on pressurized hot water, and it is where the exchanger is designed. Corrugated tube-in-tube or a multi-tube bundle keeps the product at 5 to 7 ft/s so the deposit is sheared thin as it forms. Hot water enters at 262 to 268 F, counterflow, so the wall at the product outlet is only 5 to 8 degrees above the product. A heater sized on a 20 degree approach is cheaper and hits its pressure drop limit in two hours.
HeatX sizes ESL final heaters with 20 to 30 percent more area than the clean duty, so that as deposit builds the outlet still reaches setpoint with the valve open wider, not with the water temperature raised. Raising the water to chase setpoint is the most common way to shorten a run, because it raises the wall exactly where the deposit is forming.
- U-tube steam-to-water set, water loop 30 to 40 psig above saturation
- Back pressure valve after the cooler holding 40 to 60 psig at the heater
- Pressure drop trend across the heater as the run length indicator
Plate or tube for the ESL heater
At 250 F a gasketed plate heater is possible on thin milk where the plant already stops each shift. The gaskets are the limit: EPDM at 250 F for hours a day ages in months, and the narrow channel reaches its pressure drop limit on a thin deposit. The tubular heater is the standard answer on lines that want 8 to 12 hours between cleanings, on anything over 12 percent solids, and on anything with fiber or stabilizer.
The common mistake
Treating an ESL heater as a hotter HTST heater. HTST sections are sized close, on a small approach, for a run of a shift. An ESL heater sized that way, without the preheat hold and without area margin, meets setpoint for an hour and then needs its hot water raised every hour until the CIP. The line sold as a 12 hour line runs 3, and the real fault was a hold coil never installed and 25 percent of tube length value-engineered out.
Send the product and solids, the flow, the setpoint and hold, the run length needed and the steam pressure for the hot water set. Call and talk it through with an engineer: 1-805-484-2992
ESL heating process conditions
The heating train is described here as the sizing basis: preheat, hold, final heater and the pressure that keeps the product liquid. Compare your setpoint and run length with it, then send your figures for quoting.
| Condition | Detail |
| Product | Milk, creamers, flavored milk, oat, almond, soy and pea drinks, 8 to 25 percent solids |
| Flow range | 3,000 to 40,000 lb/h, one skid per line |
| Temperatures in / out | 40 F raw; 195 to 205 F after preheat; 250 to 260 F at hold inlet |
| Hold | 30 to 90 seconds preheat hold at 195 to 205 F; 2 to 4 seconds final |
| Utility | Pressurized hot water at 260 to 275 F from a steam-to-water U-tube set |
| Approach | 5 to 10 degrees hot water to product at the heater outlet |
| Construction | Corrugated or multi-tube final heater; plate or tubular preheat regenerator |
| Finish / class | 3-A, 316L, 20 to 25 Ra, welded product path |
| Product pressure | 40 to 60 psig at the heater to stay above saturation; 150 psig design |
| CIP | Caustic then acid; designed to run 8 to 12 hours between |
Common FAQs
Typically 250 to 260 F for 2 to 4 seconds for milk and creamers. Some lines run 240 F with a longer hold; some reach ESL shelf life with microfiltration plus HTST heating.
Water boils at 255 F at about 33 psig. Below that the product flashes and the hold disappears. A back pressure valve after the cooler holds the hot section 15 to 20 psi above saturation.
On milk, a 60 second hold at 200 F typically stretches the run from 2 to 4 hours out to 8 to 14. On oat drinks the gain is smaller because starch fouling does not respond.
Not on the product exchanger. Plant steam gives a 300 F wall on a 250 F product and fouls at once. Steam heats a pressurized water loop through a U-tube set, and the water heats the product.
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