Lettuce Washing

Super markets, fast food chains, restaurants etc., very often use pre-packed lettuce. Hygiene codes and quality control (HACCP) contribute to optimized food safety and the interest of the customer.


The quality requirements for lettuce are stringent, e.g. zero tolerance on Salmonella, Listeria and E-Coli. Further the appearance must be good, the lettuce must pass high standard test criteria (no chlorine taste) and the micro biological surface contamination is subject to stringent rules. In addition to this the customer may prescribe a shelf life when the lettuce arrives.

Quality Requirements

  • Salmonella: zero
  • Listeria: zero
  • E-Coli: zero
  • Must pass sensory evaluation test criteria (no chlorine taste)
  • Appearance of lettuce must be good.
  • TPC must be within guidelines at day 10. (TPC= Total Plate Count microbiological surface contamination)

Old Process Description

  • High levels of chlorine (100-300ppm) from sodium hypochlorite 12.5% are used in the washing water causing a very strong chlorine smell in the factory and affecting employees (eye & skin irritation, high employee illness rate) and the environment
  • The high level of chlorine disturbs the pH-level control of the washing water
  • To maintain chlorine residual high cost for chilling and extra ice are required as a lot of water is dumped;
  • The level of Salmonella, Listeria and E-coli is not always zero;
  • Permanent concern for Listeria contamination as Listeria is not affected by Chlorine at lower water temperatures;
  • The micro biological surface contamination is from the start inconsistent.
  • Impossible to control chlorine residual and requires manual chemical addition every 15 minutes
  • pH control not possible as always increasing.
  • TPC at day zero was inconsistent (usually 1 x 105, 3 x 105, 1 x 106 counts)

Description of GO2TM based system

  • GO2TM solution at 1.0ppm in 2 stage wash. First wash stage is 46°F (8°C) and second wash stage is 35°F (2°C)
  • Dosing is done automatically using GO2TM solution storage tank, automatic residual control and a dosage pump (Acid resistant, equal to Prominent B-Line).
  • Operators check on the dosing equipment +/- hourly but do not add any chemical manually.
  • pH is automatically controlled to 7.5
  • Very little dumping of water and only chilled water is used.
  • E-Coli is 100% eliminated and the count is always zero.
  • Listeria concern is eliminated. GO2TM solution 100% kills Listeria at low temperatures.
  • TPC at day zero is consistent and always less than 7 x 104
  • To ensure the residual of GO2TM in the wash water the use of a redox meter is strongly advised in combination with dosing equipment (dosage pump, contact water meter, two PE-HD black storage tanks and an injection point).
  • Contact time is key during the washing process.

Advantages / Benefits

  • The use of GO2TM in the wash water will contribute to an increased production yield by better optimized micro biological control
  • No more use of chlorine in the disinfection process
  • No taste or odor problems with lettuce
  • Increased shelf life of the lettuce
  • GO2TM is effective against fungi; a separate fungicide may no longer be required.

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