Defrosting Prawns Safely

Dear All,

Any help with the following would be appreciated: the food safety program that governs our activities states that all food is defrosted under refrigeration or microwaved. Which is fine. However, I have noticed, in a number of food service kitchens, frozen prawns are routinely taken out of the freezer in their bag and defrosted in cold water just prior to use. IMO this is more workable and doesn't compromise product safety. But I need some evidence to validate this practice. I have found a procedure for thawing frozen prawns for sampling, examination & analysis in Codex Stan 92-1981:

"The sample unit is thawed by enclosing it in a film type bag and immersing in water at room temperature (not greater than 35ºC). The complete thawing of the product is determined by gently squeezing the bag occasionally so as not to damage the texture of the shrimp, until no hard core or ice crystals are left."

The sampling, examination & analysis in the above codex std can include checking for flavour. So is this enough? Or does someone have some other evidence?

Thx, in anticipation,
Toni
 

As I type this anecdote I know it probably won't be of any use to you. I’ll tell it anyway to buy a little time until the cavalry arrive.

I buy frozen prawns a lot and usually get them out of the freezer a couple of hours before I need them leaving them to defrost at room temperature in a dish with a clean towel over the top. If I get the timing a bit wrong and they defrost too early I put them in the refrigerator if they’re still frozen when I need them I run them under the cold tap for a couple of minutes. It's never caused me any illness.

I don't suppose this is acceptable to the scientists.

Regards,
Simon

Thx Simon. Its always nice to get a reply. We do the cold water at home too.

Toni

Dear Toni,

Not quite sure whether you were referring to RTE shrimp or not.? Also not quite sure by “defrosting” you meant fully thawed or deglazed? I presume fully thawed.

I suspect you are slightly comparing 2 procedures with somewhat different objectives.
I guess the Codex ref. is designed as an analytical method to also allow the routine assessment of fully thawed net weight hence the specific instructions (probably for non-RTE shrimp since the latter are typically based on deglazed weight IMEX?). It is not really intended as a “process” method. Nonetheless, the result for RTE shrimp is a fully edible product and this route is routinely used to evaluate organoleptic qualities, including eating. Never buy this stuff myself but I am surprised if you didn’t find a recommended procedure invoving thawing on the back of the bag occasionally ?
The “kitchen” technique (and large-scale) for frozen product in general involving thawing in flowing water is discussed in some other threads here, eg for raw kitchen chicken, with, from memory, validations via links to the official USFDA website amongst others. Comparisons to microwave etc are also made. Don’t remember specific mention of shrimp, raw or RTE, though. The usual (general) practical problem is time if you maintain low temperatures as usually preferred, especially for large size product and sizable quantities. Some analytical users don’t like the Codex method above due to claimed “unfairly excessive” drip losses so also demand the use of a plastic bag.

This is quite a complicated topic and I am not very familiar with chef methods so my apologies if I’ve misunderstood yr original post and complicated things even more . Please clarify if so. You mention safety. Well, as usual, I guess it depends how you control the (presumably) RTE procedure. As Simon described, it can certainly be done safely on his scale. Or are you more concerned with relative flavour losses etc ? or microbiological ?

Rgds Charles.C

Charles,

Thx for your thoughts. I am interested in defrosting (fully, not deglazing only) of quick frozen raw or fully cooked prawns.

I basically believe there is not a problem with the current practice, but I require the evidence to back up my position. You are right making the point that: "It is not really intended as a “process” method." But do you think I can still use it given that the end result is a product that can be eaten/tasted? (The Codex Std, also gives cooking methods for raw prawns, after this defrosting method, prior to flavour testing. This Codex method applies to quick frozen raw or partially or fully cooked shrimps or prawns, peeled or unpeeled). I realise this is abit round-about, but I think its reasonable.

I am purely interested in micro safety. The texture/taste etc have proved not to be an issue regardless of which defrosting method is used i.e. in refrigerator or water.

Looking forward to your reply,
Toni

(Extra thought; sample size could obviously prove a problem. Codex sample unit is 1kg. I am just confirming the size of the bags we use and will post when I get it)

Toni

Dear Toni,

(Extra thought; sample size could obviously prove a problem. Codex sample unit is 1kg. I am just confirming the size of the bags we use and will post when I get it)

Indeed, this is relevant. I presume (hope) yr shrimp is IQF only. How long does it take to thaw yr typical bag of shrimp in water maintained at say max 10degC ? 1hr ? Is the space involved a problem, ie how much quantity involved / day? What are you doing with the shrimp next, especially the RTE, shrimp cocktails ?
IMEX, the plastic/air is an excellent thermal barrier unfortunately which is one reason why many labs don't like this procedure. Also, unless you maintain good temp. control micro things start growing of course. For well glazed, block frozen shirmp, it becomes almost unworkable at kg levels unless you use warmer water.

Rgds / Charles.C

Charles,

The bags are 1 kg - which is good news. They would only be done one at a time. So do you think I can quote the Codex std as validation for the defrosting? Then follow up with a time requirement after which the defrosted prawns are transferred to a bench top refrigeration unit before undergoing cooking/plating up?

IQF ???

Thx
Toni

Dear Toni,

IQF is Individually Quick Frozen, ie frozen, separated pieces thaw a lot faster than well-glazed shrimp blocks.

If you are only looking for an “authoritative” ref. regarding the safety aspect of the step “thawing shrimp using water”, this FDA link which is as far as I can see is perfectly general should work OK. It also spells out the scientific logic involved. (Whether yr subsequent microbiological check will validate this recommendation will depend on how well you control the process and what yr micro. FSO is ?) –

http://www.fsis.usda..._Thaw/index.asp

If you additionally prefer a re-statement specifying seafood, can try this attributed to the FDA consumer, (see under “preparing”) –

http://www.pueblo.gs...od/797_sea.html

(Yr Codex link is not exactly unusable IMO but not primarily aimed at the safety aspect. I thought the above was a bit more "direct" )

Although not explicitly stated, I think the above links are targetted particularly at raw foods (as per yr last post) although a similar thaw logic applies to RTE products. The necessary control and FSO for RTE will then clearly be more sensitive (CCP?), not to mention the handling factors.

As I’m sure you know already, there are literally hundreds of anecdotal opinions on IT as to which is the best way to thaw from a quality aspect. The problem is often comparing apples and oranges of course.

added - as an example of a "rear of packaging" suggestion I saw this on IT -

Thawing

Q: What is the best way to thaw XX Frozen shrimp?

A: Thawing instructions are conveniently located on the back of our packaging. In order to maintain the very best quality of our frozen shrimp, we recommend the following thawing procedures.

Recommended Thawing Instructions

Place frozen XX Shrimp into a strainer or colander and cover with aluminum foil or plastic wrap. Place drip pan underneath strainer and refrigerate overnight (approximately 12 hours). Rinse for 10 seconds under cold running water and let drain for two minutes.

Quick Thawing Instructions

Completely submerge frozen XX Shrimp into a bowl of cold water for approximately 20 to 30 minutes. Transfer shrimp to a colander/strainer. Rinse for five seconds and let drain for two minutes.

http://www.contessa.com/faqs/

(seems to assume pre-removal of bag as per the Simon methodology but drops the towel )


Rgds / Charles.C

All good stuff but what I thought while reading this is if you can't find an authoratitive source which answers all your questions, why don't you trial it at worst case scenario? Take the water temperture you are intending to use and either (if you have the equipment) datalog the prawns or periodically pierce the bag and probe the prawns before resealing. I'd also do some micro testing on the prawns themselves, I suggest sending off samples straight from the frozen bag; defrosted the traditional way and then using this fast defrost.

I've used prawns before in maufacturing and if I wasn't able to defrost them more gently, we'd empty the bags into a single layer in a tray, covered and defrosted more quickly at room temperature monitoring them until they reached no higher than 2 degrees C at which point they were used or put back in the fridge. Using something like this means (I believe anyway) that you don't need any fancy evidence for validation because you are chilling way before 5 degrees C is reached and so minimising the risk from most bacteria. I don't know what peoples thoughts are, I've done similar things with chicken before. I would suggest it's less risky than using warm water which might create a warm surface on some of the prawns nearer the edge of the packaging?

Charles & GMO,

I am working on this over the next 2 weeks, so I will read though your comments & links and let you know how I go.

Thx
Toni

Tony, what is the intended use of the defrosted prawns? Are they to be served immediately (or withing a few hours) to the final customer or are they to be used in the manufacturing of a ready-to-eat product (e.g. pre-packed prawn cocktail with several days shelf-life)?
It is standard procedure in Ireland and backed by the relevant Irish Standard to defrost small quantities of frozen prawns under running cold water. The procedure would be to place the frozen prawns without a bag or wrapping in a sieve or colander and rinse them with cold water until they are fully defrosted. Due to the small size of individual units, this does not take long. Water and any microbial or other contaminants have to be able to drain off during defrosting to prevent bacterial growth or further contamination of the product. Stagnant water or prolonged exposure to high temperatures (e.g. lukewarm water, room temperature) is not advisable due to the highly perishable nature of the product. Unfortunately, this defrosting method lets the prawns loose some of their flavour due to the rinsing.
IMO this method is not suitable for prawns that are to be used in a product with several days shelf-life. In this case, the prawns should be defrosted in a temperature controlled environment (e.g. fridge) for maximum control.
If you need to be 100% sure and have evidence of the safety of your product, monitor the temperature of the prawns during defrosting and ensure that it does not exceed 5ºC (or whatever your national limit for chilled ready-to-eat products may be) during or after defrosting.

Greetings form Ireland

Matt

Charles & GMO,

I am working on this over the next 2 weeks, so I will read though your comments & links and let you know how I go.

Thx
Toni

Dear Toni,

Have you worked over it. We use cold running water or sometimes place it in the chiller a day before.

Matt & Jean,

Sorry for my delay and thank you for your replies -> I've been doing a course and with Xmas & holidays etc etc. We are going with the defrosting in water as per the CAC listed in my original post. Temperature/time monitoring is going to be carried out on a regular basis.

Matt: the prawns are to be served immediately. Thx for the info re the Irish procedure.

Thx
Toni