Sous-vide experiment: temperature vs. duration

You didn't think my last post was the end of my sous-vide experiments, did you?  Sure, I sounded a tad too pessimistic about the world's latest and greatest cooking method.  But my testing is only starting.  I have since cooked 4 more steaks and have some findings about the temperature and duration variables.  

My goal is to analyse the factors that impact the juiciness of the meat cooked using the sous-vide method.  I repeated last weeks experiment of measuring the steaks' weight during all stages of cooking and measuring how much juice a steak releases during serving.  Here are the details of my experimental set up:

Steak cut and thickness: Rib-eye 1 - 1.5 inches thick.  I used only the "eye" muscle to eliminate variability due to the difference in the fat content (the flap of the rib-eye tends to be fattier and juicier and it was impossible to give each steak exactly the same amount of flap). I tied the steaks with butcher twine to keep their shape uniform (within each steak).  This worked great for vacuum sealing preventing the usual tapered edges.

Salting:  I skipped the salt completely for this experiment to simplify things.

Searing: all steaks were seared for exactly 50 sec per side.

Measuring juiciness: Since collecting quantitative data on juiciness by means of chewing a steak is not very practical, I decided to slice the done steaks 1/4 inch thick, pour off the juice that they released into a cup and weigh it. I have a tea scale that can weigh very small amounts accurately.

To rest or not to rest: I didn't rest any steaks after searing since that's the best practice of sous-vide cooking.  I actually have some doubts about this practice and am planning to set up an experiment to test the effects resting has on meat cooked using the sous-vide method.

Doneness: Since I cooked the steaks at different temperatures (121F, 126F, and 131F), final doneness varied.

Cooking duration: I cooked 3 steaks for a relatively short time (50 - 100 minutes) and 1 steak for a long time (5 hours)

Steak A: 121F water bath for 50 minutes

Thickness: 1 inch

Weight before cooking: 114g = 100%
Weight after water bath and thorough drying: 108g = 94%

Temp after water bath = 119F*
Weight after sear: 102g = 89%
Internal temperature after sear = 119F
Weight of juice after slicing: 4.12g = 3.61%

Steak B: 126F water bath for 50 minutes

Thickness: 1.25 inch

Weight before cooking: 124g = 100%
Weight after water bath and thorough drying: 117g = 94%

Temp after water bath = 123F*
Weight after sear: 107g = 86%
Internal temperature after sear = 130F
Weight of juice after slicing: 9.3g = 7.5%

Steak C: 131F water bath for 100 minutes

Thickness: 1.5 inch

Weight before cooking: 156g = 100%
Weight after water bath and thorough drying: 141g = 90%

Temp after water bath = 130F
Weight after sear: 132g = 85%
Internal temperature after sear = 132F
Weight of juice after slicing: 9.44g = 6.1%

Steak D: 131F water bath for 5 hours

Thickness: 1.5 inch

Weight before cooking: 150g = 100%
Weight after water bath and thorough drying: 124g = 84%

Temp after water bath = 130F
Weight after sear: 114g = 76%
Internal temperature after sear = 135F
Weight of juice after slicing: 2.4g = 1.6%

* Steaks A and B were a little short of the desired internal temperature, but 1 and 2 degrees respectively.

Results

The findings from steak A, B, and C is not a surprise.  It can be explained by the fact that the juices start to release from the meat fibers around 120F.  But all steaks cooked relatively quickly by sous-vide standards (50-100 minutes) were juicy.  What made the biggest difference is not varying the temperature, but varying the cooking duration.  Steaks C and D were technically the same doneness, but the steak that was left in the water bath for 5 hours released 1.6% of juice instead of 6.1%.  This explains the lack of juiciness of sous-vide steaks in my last experiment.  They were cooked in the water bath for 3.5 hours.

What most sous-vide books and websites tell you is that you can't overcook using the sous-vide method.  It all depends on how you define "overcook."  The steak will not go above the desired temperature no matter how long you hold it in the water bath (well, dah!), but the longer you hold it, the more juice you lose.

How long is too long?

It depends on the thickness of meat of course, but here is some data for 1.25-1.5 inch steaks:

131F for 100 minutes -- 6.1% juice release during serving

131F for 3.5 hours -- 1.93% juice release during serving

131F for 5 hours -- 1.6% juice release during serving

I am sure half an hour doesn't make much difference, but 3 hours do.  If you are using the ghetto sous-vide set up, you'll probably never run into this problem.  Who wants to monitor the water temperature for an extra few hours?  But if you are using an immersion circulator, you might be tempted to put meat in the water bath whenever it's convenient (in the morning before going to work, during kids' nap, etc) and then have it ready for dinner.  It will surely be very tender, but you'd better have a lot of demi-glace handy because it will be dry.

So where does this leave us?  Do I still think sous-vide sucks?  The good news is that I was able to get a steak that is as juicy as Kenji's oven method.  The bad news is that it takes about 3 times longer with the sous-vide method.  It is not active time, of course, but I need to be home to put the steaks in the water bath 1.5 hours instead of 30 minutes before the meal.  

Here is a summary of sous-vide vs. oven method pros and cons

Sous-vide pros:

• Oven is free to cook other dishes.
• Meat can be held at desired temperature for close to an hour with no ill side effects.  It can even be held longer (juiciness will be reduced, but tenderness won't be compromised -- if anything it will get more tender).
• No last minute monitoring with a thermometer, freeing you to work on other things.

Sous-vide cons:

• Requires either a lot of baby-sitting or a lot of expensive equipment.
• Takes way longer than the oven method (about 3 times as long).
• Takes a lot of counter space.
• All servings will have the same doneness.  I don't think it's a biggie.  Most people in my family now know to trust me on doneness :)

Oven pros:

• A lot faster than the sous-vide method
• No expensive equipment
• If different donenesses are desired, some pieces can be started in the oven earlier.

Oven cons:

• Need to keep the oven at a low temperature, so most vegetable side dishes would have to be done in advance.
• When the meat reaches 95F (or some other desired temperature), it has to be seared and served.  Can't be held at a steady temperature.
• A little last minute monitoring.

What next

I am tempted to test the theory that sous-vide cooked meats don't need resting.  It's true that the temperature doesn't need to come to equilibrium like it does for traditional methods (it already is at equilibrium).  But I am wondering if the steak would hold its juice better if it rested.