Tuesday, June 14, 2011

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.
 

16 comments:

Dave said...

I enjoy these posts, thanks. You can easily go between the ghetto sous vide and the supreme, I built a sous-vide crockpot setup that's accurate to around 1 degree C for about 20 bucks so it's reasonable to fool around.

I had pretty good luck with a pork shoulder at a reasonable high temp (170), though I haven't had a chance to repeat the experiment yet.

Mark T said...

it does take longer but you get a better product in the end. There is no way that you can do a medium rare short ribs in a regular oven. In the end I do a lot of my cooking in a water bath now.

Helen said...

Hi Mark,

That's right -- you can't do 130F shortribs in the oven. But even though those short ribs would be red inside and 130, they would be very different than a juicy medium-rare rib eye. I am not saying better or worse, just different. The dishes I was talking about in this post are the ones done with tender cuts of meat (rib, loin, tenderloin, sirloin, etc). for those, I do believe that the oven method produces just as wonderful of a result as sous-vide.

Cheers,
-Helen

Anonymous said...

Helen, I can't help but admire your scintific approach time and time again! This is fascinating!
Remaining your huge fan,
Yulia

Anonymous said...

Thanks for posting this! Very helpful.

I just cooked my first dish with a Sous Vide Supreme, and your posts confirmed my suspicions that I'd cooked this too long.

I cooked a Kobe top sirloin for about 7 hours at 128 degrees; while the done-ness was about perfect, and it was pretty tender, it was overly dry, alas.

I bought the Sous Vide Supreme to cook elk steak, fingers crossed on finding a technique that's not overly drying.

Niki said...

Hi Helen

I followed your instructions step by step but failed to get Steak B.
Was it due to poor meat quality?
Did I miss something else?
BTW are you planning on offering some sous vide training?

Helen Rennie said...

Hi Niki,

Can't you give me more details? Was it too raw, too cooked, too dry, too chewy, etc? What cut did you use? How thick was it? How long did you cook it? What sous-vide set up do you have? How long did you sear? When did you salt?

Cheers,
-Helen

Niki said...

Hi Helen
Just to make myself clear here are my answers:
Can't you give me more details? Yes
Was it too raw, too cooked, no, it was cooked to perfection.
too dry - yes
slicing the steak the way you did it, didn't make it shed any "blood" (miyoglobin)
too chewy - yes
What cut did you use? Ribeye steak
How thick was it? same as yours in your test
How long did you cook it? 100 and 130 minutes
What sous-vide set up do you have? I don't understand the question.
How long did you sear? 50 sec per side
When did you salt? did not salt

Helen Rennie said...

Hi Niki,

Thanks for your answers. Now I can help :)

Note that I cooked steak B for 50 minutes at 126F and you cooked yours for 100 min at 130F (I wasn't sure -- you said 100 and 130 minutes). This idea that you can't overcook using sous-vide is a myth in my opinion, and that's what my blog post was about. You can't get above a certain temperature. But the steak will start to lose liquid and the longer it sits in the bag, the more liquid it will lose.

Another thing to note is that the temperature will rise during sear, so I prefer to sous-vide my beef below 130 to give it a chance to finish cooking in the skillet.

About the sous-vide set up: some people use a sous-vide supreme machine, some use a huge beer cooler, some use a pot of water on the stove with a thermometer. The accuracy of temperature can vary depending on the method. Sous-vide supreme is usually the most accurate method (short of a real immersion circulator).

The chewiness can be effected by temperature, but since you were in the ballpark temperature wise, I am guessing the quality of the steak had more to do with it. In the experiment, I only used the eye (the center muscle) of the rib-eye. All rib-eyes have a gristle running through them. It will be chewing no matter what you do, but it's easy to remove after cooking. If the entire piece was evenly chewy, I am guessing it was a fairly lean rib-eye. Where was it from?

Cheers,
-Helen

AzHP said...

I posted this in your article about why sous vide sucks but I think this is a more appropriate place for it: but did you use a vacuum sealer or the zip loc method for this? I have noticed this same phenomenon of juiciness leaving the meat when using a zip loc bag for many hours, but I am not sure if this is caused by the cooking method or the lack of a true vacuum seal. It'd be interesting to know the comparison between a vacuum sealed steak and a zip loc sealed one both cooked for the same amount of time in the same water bath.

Helen Rennie said...

The steak was vacuum sealed, not in zip lock bags. The loss of juice would happen either way.

Trabob said...

I am real curious about the dryness in steaks as to where the juices go, as I was unaware that water (juice) could escape plastic sealed, as my reason for considering sous vide is to keep the vitamins inside for health reasons, so if liquid is escaping I am now concerned about losing vitamins, also would it help to inject water into the meat prior to cooking it sous vide< thanks
Trabob

Helen Rennie said...

The liquid is in the bag.

Trabob said...

Ok thanks
so does anyone know if the juices have the nutrients in them as that was one reason I went from a juicer to a blender because so much of the nutrients are in the pulp left over from the juicer, and if a lot of the nutrients are lost in the juices would it at least add juice back in by injecting water or oil into the meat? Thanks

Helen Rennie said...

I don't know about nutrients. I only know about taste. Try not to hold the food in a water bath longer than necessary and you won't lose much juice.

Trabob said...

OK thanks, you should get a job as a food tester, sounds like you would be good at it