Oil Corrosion
VOL. 20 NO 9
The last issue of Gem Memo included a discussion about corrosion, occurring in fryer systems, caused by cleanup chemicals. Unfortunately, this discussion contained a technical error. A big thank you to the sharp-eyed reader, a chemist, who caught the error and kindly set the record straight. The Memo stated, "If a pipe weld does not have a proper root pass, a very narrow U shaped slot will be left around the inside of the welded joint. Caustic collects in this slot and often will not be flushed out." The last sentence should have read, Acid used to neutralize the cleanup caustic collects in this slot and often will not be flushed out. Continuing the correction, the minute amounts of acid left in this slot will react with the metal while the fryer is in operation. Over a period of years, this small amount of metal lost with each cycle, will result in failure of the welded joint. Threaded joints have a similar exposure to corrosion caused by neutralizing acid.
Operating and sanitation personnel need to be aware of the necessity to make sure the acid is flushed out before the fryer is put back in service. Allowing enough time to adequately flush out all traces of acid is much easier said than done. Plant personnel are always under pressure to get cleanup finished, so the fryer can be put back into service as soon as possible. Since flushing is the last operation, it is most likely to be cut short. Unless your fryer systems are perfect, make sure enough time is allowed to flush out the acid. Better yet, have a qualified chemist set up a procedure to make sure no acid is trapped in the nooks and crannies of the fryer system at the end of the cleanup cycle.
Last month's Memo covered Gem's ongoing effort to reduce oil volumes in french fry fryer systems. The justification for this reduction was not covered. Processing parameters and economics provide the incentive to minimize oil volume. Fryer oil degrades at a rate determined by temperature and influenced by impurities in the oil. For the purpose of this discussion, potatoes, water vapor and air are considered impurities. Potatoes absorb oil during the frying process. Oil removed by the potatoes is replaced with fresh oil. The ratio of total system oil volume divided by the amount of oil removed by product every hour determines oil turnover rate, which is expressed in hours. For optimum operation, oil turnover should be no longer than twelve hours. To reduce oil turnover time, it may be necessary to bleed off some oil. If the plant has a fryer with a fast oil turnover, the surplus oil can simply be transferred to that fryer. If not, the economics are not pretty. Not only does the plant have to purchase oil that is not being sold with the product, a cost may be incurred for the disposal of the used oil.
It appears that french fry potato fryer technology is ahead of most other fryer applications. Gem recently modified a specialty product (not potatoes) fryer. Reports from the customer indicate that this fryer is now producing product with more uniform surface texture and color than competitor's units. In addition, frying oil temperature, in this fryer, is less sensitive to changes in product loading. Technology, developed by Gem Equipment for french fry potato fryers, was utilized in the design of this fryer modification.