Ahi tuna, also known as yellowfin tuna, is a popular fish used in sushi and other dishes. However, like many fish, ahi tuna may contain parasites that can be harmful if consumed raw or undercooked. Proper handling and preparation of ahi tuna is important to kill any potential parasites and make the fish safe to eat.
What types of parasites can be found in ahi tuna?
There are a few main types of parasites that may infect ahi tuna:
- Nematode roundworms – One of the most common is the Anisakis nematode. Anisakis cannot be killed by salting or pickling, only by thorough cooking or freezing.
- Tapeworm larvae – Tapeworms may be present in raw or undercooked tuna. Tapeworm larvae cannot be killed by salting or pickling.
- Flukes – Parasitic flatworms that can infect the flesh and organs. As with other parasites, they are only killed by freezing or cooking.
Other parasites like cod worms may occasionally be found in tuna as well. Freezing or cooking is necessary to kill any parasites present.
Why are parasites a concern with raw tuna?
Eating raw, undercooked, or improperly handled tuna containing live parasites can lead to infection. Parasites may be killed if tuna reaches an internal temperature of -4°F (-20°C) for 7 days or -31°F (-35°C) until solid and storing at -31°F (-35°C) or below for 15 hours or -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours. This temperature and time is required to kill any parasites that may be present.
Some of the potential risks of parasite infection include:
- Gastrointestinal symptoms like nausea, vomiting, diarrhea
- Allergic reactions to parasites
- Digestive blockages if large numbers of parasites cluster together
Proper handling and preparation should always be followed with raw tuna to avoid any foodborne illness.
How to kill parasites in tuna at home
There are a few methods that can be used at home to effectively kill any potential parasites in tuna:
Freezing
Freezing tuna will kill parasites. Tuna should be frozen at -4°F (-20°C) or below for 7 days to kill parasites. You can check your freezer to ensure it reaches appropriate temperatures.
Steps for freezing tuna to eliminate parasites:
- Purchase fresh tuna and make sure it has not been previously frozen.
- Cut the tuna into portions no more than 2 inches thick.
- Seal the tuna in air-tight packaging. Remove as much air as possible.
- Mark the pack with the current date.
- Place packs flat in the freezer to ensure rapid freezing.
- Freeze for 7 days at -4°F (-20°C) or below. Check freezer temp to ensure it reaches proper temperature.
After freezing for 7 days, the tuna can be thawed in the refrigerator and used raw for sushi, ceviche, or tartare.
Cooking
Thorough cooking will reliably kill any parasites in tuna. Tuna should reach an internal temperature of at least 145°F (63°C) for at least 3 minutes. Use a food thermometer to check temperature.
Safe cooking steps include:
- Sear, grill, bake or broil tuna to at least 145°F.
- Make sure there are no undercooked portions.
- Allow tuna to rest for at least 3 minutes after cooking before consuming.
Well-cooked tuna can be enjoyed hot or used cold in dishes like tuna salad or sandwiches.
Curing
Curing tuna with salt may kill parasites, but research is limited. One study found that salt-cured tuna held at 68°F (20°C) for 28 days killed parasites. However, freezing or cooking is still recommended to be safe.
Pickling
Pickling tuna in vinegar does not reliably kill parasites. Only thorough freezing or cooking should be relied upon.
How sushi restaurants kill parasites
Sushi restaurants have systems in place to kill parasites and serve safe raw tuna:
- Tuna is frozen to the proper temperature and duration to kill parasites before being defrosted and served raw.
- Precise documentation is kept on the temperature and length of freezing.
- Tuna is defrosted in small batches as needed to prevent refreezing.
- High-quality tuna is used and thoroughly inspected for any signs of parasites.
- Strict standards are followed for refrigeration and storage.
Reputable sushi restaurants are very careful about parasite control methods to avoid foodborne illness. At home, it is safest to rely on thorough freezing or cooking of tuna.
Can you eat raw tuna without freezing?
It is not recommended to eat raw tuna without freezing, even from high-quality fish markets or restaurants. The only way to fully guarantee tuna is free of parasites is proper freezing or cooking. Tartare, sushi, ceviche and other raw preparations should only be made from tuna that has been frozen for the appropriate duration at adequate temperatures.
What are visual signs of parasites in tuna?
When inspecting fresh tuna, look for these signs that may indicate the presence of parasites:
- Visible worms or larvae
- Dark spots or trails on the fish flesh
- Deformation, holes, or unusual textures on the surface of the fish
- Unpleasant “fishy” odor
- Discoloration of the gills or meat
Tuna exhibiting any of these signs should be discarded. Only use fresh, sushi-grade tuna with no discoloration or obvious parasites.
Summary of killing parasites in tuna
To summarize key points on how to kill tuna parasites:
- Freeze at -4°F (-20°C) or below for 7 days
- Cook to an internal temperature of at least 145°F (63°C) for 3 minutes
- Avoid eating raw tuna that has not been frozen or cooked
- Inspect tuna carefully and discard any with signs of parasites
- Trust sushi restaurant suppliers to use proper freezing protocols
Following proper handling, freezing, and cooking procedures will kill any parasites present in tuna and allow you to enjoy safe, delicious ahi tuna dishes.
Frequently Asked Questions
Can you eat raw tuna straight from the fish market?
It is not recommended to eat raw tuna directly from a fish market or grocery store without freezing it first. Freezing is necessary to kill any parasites that may be present. Raw preparations like sushi and sashimi should only be made from frozen and thawed tuna.
Is tuna sushi safe regarding parasites?
Yes, tuna prepared for sushi at restaurants is very safe when proper freezing guidelines have been followed. Reputable sushi restaurants always freeze their tuna to the appropriate temperatures needed to kill parasites before defrosting and serving the fish raw.
Can salt cure tuna parasites?
Salt may potentially kill parasites in tuna, but it is not a fully reliable method. Research on salt curing tuna has been limited. For guaranteed parasite destruction, the FDA and other food safety organizations recommend only proper freezing or cooking.
Why is fresh tuna sometimes banned from being served raw?
Some local health departments may ban serving raw fresh tuna at restaurants that has not been frozen. This precaution reduces the risk of parasites, even though tuna providers may follow “best practices.” Freezing is the only sure way to kill all parasites, so bans on raw fresh tuna help prevent potential issues.
How should you store tuna to prevent parasites?
Raw tuna should be stored at under 40°F (4°C) for no more than 3 days after catching. Use fresh, raw tuna immediately if not freezing it. If freezing, divide into portions, vacuum seal, and freeze at -4°F (-20°C) or under for at least 7 full days to kill parasites.
Conclusion
Ahi tuna is a delicious fish enjoyed raw in many dishes, but it may contain dangerous parasites if not handled properly. To kill any parasites present and make tuna safe to eat raw, it must be frozen at -4°F (-20°C) or below for at least 7 days before being thawed and prepared. Cooking tuna thoroughly to an internal temperature of 145°F (63°C) also reliably destroys parasites. Take care to inspect tuna closely and discard any fish showing signs of parasites. Follow the proper protocols of reputable sushi restaurants if enjoying raw restaurant tuna. With the proper handling, freezing, and cooking, you can safely eliminate parasites from ahi tuna and enjoy its amazing taste and texture.