Let’s take a quick review of what I have discussed thus far in the Ask Don ?  section on atuna.com, before moving on to thawing or de-frosting tuna. In my first answers I talked about the importance of taking correct and accurate backbone temperatures during processing. Backbone temperature is one of the best ways to determine when to start and finish processing steps. It is also the key measurement for assuring quality while receiving and maintaining raw fish. My second article talked about properly sizing tuna and its importance. Tuna that are the same size will have the same target backbone temperatures and will assure optimum processing times. This will eliminate having a wide range of backbone temperatures which will result in under and over processing. Up to this point, we should all know how to achieve these 2 important guidelines.

We have already accurately sized all our tuna so now we will bring them out of the cold storage for processing. The most common mediums for thawing tuna are air, water, and steam. Let’s first state our objective in thawing: To assure that all fish are equally thawed to within the same backbone temperature during the same time cycle. Most canneries thaw fish in large plastic or steel container boxes that hold from .5 ton to 1 ton.

The common practice is to air thaw overnight simply by taking them out of the freezer the night before processing or to have a scheduled regimen for circulating water within each container. Other techniques include filling the container with water and just let it set until the fish are thawed. Some canneries inject steam into the water to make the thawing faster. All of these will work but some better than others.

The biggest problem with thawing is that the surface layer of fish will always thaw first due to it being exposed to the air or the water might be sprayed from the top of the container. Even though the top fish are thawed, the fish in the center are still frozen. The result is that you have to over thaw the surface fish in order to thaw the fish in the center. Over thawed fish will quickly decompose and become spoiled if the temperature elevates. Also if some fish are exposed to the air while the others are under water, then this will  result in under and over thawing. Normally if the container is not overfilled where all the fish are below the water line and water is circulated from the bottom to the top, then you will achieve optimum thawing with a minimal backbone temperature range. It is also important that your water is potable or chlorinated to reduce bacterial growth. Always remember that you should take accurate backbone temperatures, properly size all your fish, have a set time schedule based on fish size to determine your thawing time, and follow the guidelines that I just discussed for the best thawing results.

Please mail your questions to: askdon@atuna.com

Read other Ask Don ! articles