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Preparing Metabisulfite Solutions
To Prevent Black Spots on Harvested Shrimp
Ara Bardakjian (email@example.com): Dear Shrimp News:
My name is Ara Bardakjian. The reason for my email is to ask you if you could please help me understand how to prepare a diluted solution of sodium metabisulfite to prevent melanosis, black spot, on my harvest. I don’t know how many grams of sodium metabisulfite I should dissolve in a liter or 100 liters of water to preserve 500 kilograms of freshly harvested shrimp. I’m starting a small super intensive shrimp farm with an initial output of six metric tons of shrimp per year, and hope to harvest 500 kgs a month.
Bob Rosenberry (firstname.lastname@example.org): I don’t know the answer to your question, but I’m sure if you posted it to The Shrimp List, you would get a lot of good answers. Here’s some information on The Shrimp List:
Information: The Shrimp List is a free, email-based, unmoderated, mailing list for shrimp farmers that distributes information posted by one member of the list to all the other members of the list. Anyone can use the list to ask and answer questions, to keep participants up-to-date on a conference, to coordinate a project or to pass industry news around. You don’t have to participate in the discussion. You can just sit back and read the messages that interest you. Your email address is not completely exposed, so you can remain anonymous.
The easiest way to get on The Shrimp List is to send an email to “email@example.com”. That’s it. Just put the address where you would normally put someone’s email address, send the email with nothing else in it, and you will begin receiving all the postings to the list.
Ara Bardakjian (firstname.lastname@example.org): I sent my question to The Shrimp List, and got the following responses:
Laurent Queffelec (email@example.com): We use 150 kilograms of sodium metabisulfite, diluted in +/- 500 liters sea water, and put 400 kilograms of shrimp in this solution for five minutes. We then add four kilograms metabisulfite for the next batch of 400 kilograms. Depending on the size of the shrimp, there’s between 25 and 50 parts per million (ppm) of metabisulfite remaining in the finished product.
I don’t think this option is relevant in your case, as you may be able to use less water and keep the shrimp in the solution longer, which allows you to use much less sodium metabisulfite. I hope someone on “the list” will have a process closer to your conditions and can give you better advices.
Amirhesam (firstname.lastname@example.org): Dear Laurent, do you mean 150 or 15 kilograms sodium metabisulfite for the first batch?
Laurent Queffelec (email@example.com): The correct amount is 150 kilograms, not 15 kg, for the first 400-kg batch, then four kg for the next batch to maintain the proper concentration.
John Birkett (firstname.lastname@example.org): 150 kilograms is a normal amount in a ton of water. The duration of the bath and the salinity and hardness of your water could affect the residual.
Amirhesam (email@example.com): Dear Ara, I don’t know about your sodium metabisulfite quality, but we dissolve 10 kg in 500 liters of sea water (salinity 45 ppt) for one metric ton of shrimp (Penaeus vannamei) in a two-minute bath.
John Wigglesworth (firstname.lastname@example.org): The amounts of metabisulfite depend on your post-processing system. Chlorine inactivates metabisulfite, however, try a 2% solution of metabisulfite and a five-minute treatment on 400 pounds of product, then change and replenish your solution. Get a test kit to ensure that your residual is below 100 ppm, if your selling to the USA market.
Sources: 1. Email to Shrimp News International from Ara Bardakjian. Subject: Need Advice. February 19, 2014. 2. Email to Ara Bardakjian from Shrimp News International. Subject: Need Advice. February 20, 2012. 3. The Shrimp List (a mailing list for shrimp farmers). Subject: Need Advice. February 20–24, 2014. 4. Bob Rosenberry, Shrimp News International, March 14, 2014.
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