How to defrost a frozen tuna block 冷凍鮪柵の解凍方法

 This is a continuation of the frozen bluefin tuna block from Great-Alaska-Seafood saga. This is mostly to document for myself how best to thaw a frozen sashimi tuna block (since we have a number to which this process will need to be applied). In any case, we tried “Chu-toro” 中トロ this time. This was a relatively small  block and was perfect for the two of us. I served two slices as is (left) and made one slice into “Aburi” 炙り (right) (which was possible due to the recent acquisition of a new small kitchen torch. More about that later). This is better than the “akami” we tasted before (due to the thawing method or the fact this is chu-toro is unclear but probably both).

I made the remaining tuna into our usual “pseudo” negitoro  擬制ネギトロ. served with slices of cucumber and small sheets of nori (this is “Korean nori” 韓国のり. Since there was a bit too much tuna to  make all into “Negitoro”,  I also served one slice of tuna as well.

 

Now onto the main topic. I knew there were special instruction on how best to thaw a frozen tuna block which I may have seen on several YouTube videos. Most of the time, however, I am too lazy and just take it out from the vacuum pack, wash it in cold running water, blot it with paper towel, place it on the folded paper towel, wrap it with a plastic wrapping and thaw it in the refrigerator. This time, I looked at several instructions and decided to record the best method as far as I could tell.

How to thaw a frozen tuna block:
1. Remove the tuna block from the vacuum pack.
2. Quickly wash the surface using cold running water to remove any “saw dust”.
3. Soak it in 40C, 4% salted warm water for 3-5 minutes or until the surface becomes soft.
4. Quickly wash and blot the surface with a paper towel.
5 Wrap it completely with a sheet of paper towel.
6 Place it in the ziploc bag and remove the air, seal or Using a “Food saver” type vacuum bag and device, vacuum pack (see below).

7. Submerge the vacuum packed tuna in ice water for 1 hour or until thawed (below).

Digression alert: Every set of instructions I came across also provided some “scientific” explanation of each step. I am not sure of the validity of those explanations but the following is my understanding of the science behind each step. The warm salt water process may activate myoglobin oxidation which, especially in “akami”, makes a better red color without extracting or infusing liquid (over exposure to oxygen may make the tuna darker or “black”). Because of the much better heat conduction of water (20 times greater than air), the tuna will quickly thaw without increasing the temperature in the ice water than in the refrigerator. This process allows the tuna block to go through a -5 to -1C temperature zone which is conducive to the formation of ice crystals in the meat more quickly than if it is left to “thaw” in the refridgerator. A shorter time spent in that temperature zone supposedly improves the quality of the tuna meat because the formation of ice crystals can break the cells or form holes making the meat mushy.

As a side note, I got a new small kitchen torch since the old one failed to ignite last time. Instead of a larger torch which would use a standard size butane canister, I chose one that requires charging the butene gas like a cigarette lighter like the one I had before. Also, I had some leftover butane canisters from the previous torch I had. My reasoning was that we had a difficult time to use up and discard the standard butene canisters that we used with our old table-top gas cooker, basically because we seldom used the cooker. In any case, this one is compatible with Zippo butene canister which comes in a much smaller size.

This torch works well. It ignites easily and the flame size can be easily adjusted. I made “aburi” 炙り quite quickly with a nice char. I salted the surface before torching.