Tuna Sous Vide with Sorrel Sauce
2007-11-04
Chris Shenton
Serves 10 2 ounce portions

Sous Vide (under vacuum) cooking techniques are used by industrial food
service companies and cutting edge chefs.  We were lucky enough to get a tour
of Cuisine Solutions facilities in Alexandria VA and I immediately wanted to
try something at home.

The idea is that you cook the food in vacuum packed plastic, long and low to
break down collagen and raise the internals to the desired "cooked"
temperature.  It can then be finished, or even frozen, reheated and finished
later.  A technique I read about recently for cooking beef steak turned out
well, so I thought I'd try it for fish.

The texture and flavor of the tuna was not like any other tuna prep I've had:
it was moist, yielding, buttery/oily -- very much like duck leg confit.  I
think this is a great way to cook tuna, now that it's nearly impossible to
find top-quality fatty tuna in the US (including the deplorable frozen,
"sashimi grade" stuff that tastes like a wet sponge).

The following was cooked for 10 people as part of a cook-off, so the portions
were about 1/3 what you'd want as a main course.  One of the guests complained
about the appearance, it was rather flat brown rather than heavily seared, and
the interior wasn't tuna-red.  We've cooked these immediately and also held
them overnight in the fridge.

20	leaves	Sorrel, washed, destemmed
20	ounces	Tuna, excellent quality (NOT the frozen "sashimi" junk)
		Lemon Zest, fine grate on Microplane
		Salt
10	leaves	Sorrel, washed, destemmed

Put the (approx) 20 Sorrel leaves, still dripping with wash water into
a heavy pot, perhaps add a bit more water, and cook down until the
leaves break down.  Use a stick blender to create a smooth texture and
cook down until it's got a sauce-like thickness.
Taste: it should be quite lemony; adjust salt if desired.
Cool slightly and load into squirt bottle.

Cut the Tuna into 10 equal-sized pieces, dust with salt, dab in zest.
Bruise each Sorrel leaf with the back of knife, wrap tuna chunks in leaves.
This lemon/sorrel treatment may be unnecessary, you can season as you desire. 

Put one or two chunks of prepared Tuna in a vacuum sealer bag, not touching
each other; remove the air, and seal.  Repeat for remaining Tuna.
Bring the Tuna to room temperature so it will cook through in the bath.

Bring a large pot of water to 135-140 degrees F; monitor to make sure you can
maintain a consistent temperature.  We used gas stoves and we had to tame the
flame with a few layers of aluminum foil over the burner flames.

Immerse the sealed Tuna envelopes in the water and hold for 30 minutes, 
rotating bags so they have equal exposure.

Squeeze a drizzle of Sorrel Sauce on each plate.
Remove each Tuna from the bath, cut open, remove the sorrel leaf wrapper.
Set on top of the Sauce, brown the top with a propane torch, serve.