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Two restaurants I know fry battered fish and breaded chicken in the same oil. I asked one of them how they prevent cross-contamination in that case and I received the following reply:

Our fish is hand battered which helps lock in the flavours and juices and we have not seen any leaching of flavour from the fish into other products. Foods are typically fried between 300 and 400 degrees (depending on product and stage of cooking) which is a very harsh environment for flavours or contaminants to survive. Even celiacs are generally fine eating products from a fryer that had other flour based products fried in the oil.

They essentially said that the heat will kill contaminants and hence cross-contamination won't happen. Is this correct? Please comment on the above claim.

EDIT:

By cross-contamination, I mean one food simply affecting or mixing with another (e.g. should someone with a fish allergy be concerned about chicken fried in the same oil?)

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    'Cross-contamination' can mean contamination by pathogens or something else harmful, but it can also refer to one food simply affecting or mixing with another (e.g. the remark about flavour, or concerns for someone with a fish allergy or religious food prohibition). The current answer refers to the former sense but if you're also interested in the latter sense you should say so
    – dbmag9
    Dec 18, 2022 at 1:18
  • @dbmag9 Thank you for the suggestion. I shall include it in my question.
    – a_sid
    Dec 18, 2022 at 1:42
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    I'm not sure I buy their explanation. People with a food allergy can have a reaction after eating food cooked in the same oil as the allergen.
    – moscafj
    Dec 18, 2022 at 3:08

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Pasteurization is usually done between 63-90 °C, (145 - 194 °F) steam sterilization at 120-130 °C (248 - 266 °F). So you can consider long frying oil at 150-200 °C (245 - 392 °F) safely to be free from any microbes.

For flavours it depends, some will vanish even at temperatures far below the boiling point, some will change and some will reman stable even at high temperatures. Also many flavours are very well soluble in fats, so there is a possibility of carrying over the flavour of one food to another. And while you probably don´t want to prapare donuts in an oil that was used for fish and onions it remains a question of personal taste if this is neccessarily is a bad thing.

Gluten needs a temperature of at least 300 °C (572 °F) to denaturate, which is beyond the temperature used for frying. Also note that as long as the dough also contains some water it will not surpass the boiling point.

Parvalbumin the proteine which is the main reason for fish allergy seems to be relatively stable against high temperatures, so it might be an issue. If you have a reason to fear it as a serious hazard for your health it probably is safer to avoid it. But for advice on personal health threats and how to deal with an allergy you better should consult a doctor or another professional with an deeper insight into your specific situation and its reguirements than this community can provide.

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  • Thank you for the response. I still am not sure if I should be worried about cross-contamination if I am frying battered fish and breaded chicken in the same oil.
    – a_sid
    Dec 17, 2022 at 22:36
  • I can confirm that gluten is a problem. I was at a bar with someone who was sensitive, and she got so bloated after eating food that had been fried in the same oil that that her stomach or intestines swelled up until she looked pregnant.
    – Joe
    Dec 18, 2022 at 22:00
  • @Joe That is scary. I hope she is okay now.
    – a_sid
    Dec 19, 2022 at 1:38
  • Additionally, can grease and fat from chicken stick to the fish that is fried in the same oil?
    – a_sid
    Dec 19, 2022 at 3:06
  • @a_sid you may safely assume that the transfer works in both ways and would also for other foods/meats.
    – Stephie
    Dec 28, 2022 at 6:23

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