How Sous Vide Meat Heats and Delta-T Cooking Explained

Hey everyone! I'm Jason Logsdon from Amazing Food Made Easy and president of the ISVA. I'm so excited to be speaking at my third Sous Vide Summit!

Today I wanted to dive into a topic that I think is really fascinating, and that is "How does meat actually heat".

There is always a ton of confusion about this topic, especially with sous vide. In my Exploring Sous Vide Facebook group we get a ton of questions along the lines of "How long do I sous vide my steak?"

What you'll normally see is a wide range of answers. For example, some of the answers from my Facebook group were:

• 45 minutes
• 2 hours
• 1 hour
• An hour per inch

But no one can really seem to agree on what the right answer is and we are ranging from 45 minutes to 3 hours.

So what is happening here?

That's is what I wanted to dive into today. Fifteen minutes from now you will have a much firmer grasp of how meat heats and have a lot of ammo for your next social media argument!

What Are the Goals of Sous Vide?

But first, when does this actually apply?

This information generally applies to all kinds of meat, with a very slight variance here and there, but it's important to remember that this really only helps with one of the goals of cooking food.

Now, there's 3 potential goals when you are cooking.

First Goal: Heat Meat Through

The first goal is to heat meat through. This applies to things like traditional steaks, many types of fish, great sous vide pork chops, and an entire beef tenderloin.

Cooking is more nuanced that this, but it's basically anything you'd be safe eating raw - beef tartar and sushi for example.

But even though you CAN eat it raw, many times we prefer to heat it to a specific temperature because of how it changes the proteins in an appetizing way or just increases the temperature in your mouth.

You can argue which version is better, but cold pizza does not taste the same as hot pizza.

And this goal, heating the food through, is what today's presentation is really all about.

Second Goal: Make Food Safe to Eat

The second goal is to make food safe to eat, usually through pasteurization. This applies to things like sous vide chicken breasts, turkey, less-good pork chops, and some fish.

These are things that you would NOT want to eat raw, and could make you really sick if you did.

Today's presentation also applies somewhat to these items, because all of the sous vide pasteurization charts times are based on thickness as well, so knowing how long something takes to heat can be very helpful.

Third Goal: Make Food Tender

The third goal is to make food tender. This applies to anything you'd traditionally braise, smoke, or cook "low and slow" like sous vide pot roast, BBQ brisket, pulled pork, anything that you have to cook over a longer period of time.

Throwing some thick short ribs on the grill and heating them through will still result in an incredibly tough piece of meat. Even though they are hot, you need to tenderize them.

Today's talk doesn't apply to this goal too much, because does it really matter if your short ribs heated through after 2 hour or after 3 hours...when you're cooking them for another 72 hours anyway?

But, if you cook those sous vide short ribs for 72 hours then chill them, you can use everything we are talking about to know exactly how long to reheat it for the next day!

So this presentation will be highly focused on that first goal, heating it through, because it's fascinating in its own right and it applies to all the other goals.

Sous Vide Heating Times Are All About Thickness

So back to figuring out how long it takes to heat meat through!

There's a few things that go into this, but the biggest one is pretty simple and even makes intuitive sense.

And that is the thickness of the food. How thick is the steak. It's the most important aspect for determining how long it takes to heat food through.

And this isn't just a sous vide thing. If you've ever tried to cook a double thick pork chop on a ripping hot grill you know how hard it is to get the center up to temperature without charring the outside of it. It's a lot harder than it is with thinner pork chop, right?

With sous vide, we have the added benefit of not overcooking the food, from a temperature perspective at least, and knowing the exact temperature we are cooking at.

So the first question you ask yourself when starting to sous vide a tender cut is "How thick is it?".

One of the tools we created is our Sous Vide Timing Ruler, and it's made to help with this. Or you can use a regular ruler and make sure you wash the raw beef off of it before your kids start playing with it again!

Once you know the thickness, you can figure out how long to cook it for. There are tables like this for how long to sous vide red meat and pork, how long to pasteurize chicken and poultry, and how long to heat fish.

This was spearheaded by Nathan Myhrvold and Douglas Baldwin's work in the eGullet message boards more than a decade ago when I was getting started. It's one of the main reasons they are both in the Sous Vide Hall of Fame today.

Now there are several tables adapted from their work. On my website I have several streamlined and simplified charts that work for the majority of cooks, as well as that Timing Ruler.

Or if you really want to dive into the science and thermal dynamics of meat I highly recommend checking out Douglas Baldwin's website directly.

How Long to Sous Vide a Steak For

So here's the times from my Sous Vide Timing Ruler, which are also in my free online sous vide charts.

If we look at the first column, "a slab of meat out of the fridge". A slab is just a steak-like shape, compared to like sous vide beef tenderloin or a sous vide roast, which heats slightly differently and is in the column next to it.

So down at the bottom you can see a 1/2" thick steak takes about 30 minutes to heat through.

If you double that thickness, the time more than doubles, it's now at an hour and 15 minutes so about 2.5 times longer.

Double it again to a nice 2" thick steak and now we are looking at 3 and a half hours, again, more than 2.5 times longer.

So if the steak you asked about in the Facebook group was 2" thick, then every recommendation you were given above was wrong. Though people don't realize this due to some interesting things we will discuss next.

But for now, we know what the final answers to "How long to heat a steak for" are. You simply measure the thickness and cook it for however long one of the reputable tables says.

That's really all there is to it for tender cuts of beef, lamb, and other red meats. Anything that just needs to be heated through will work perfectly using this method. There are also similar tables for pasteurization of chicken, pork and turkey that we'll get into.

But simply measure the thickness, look up the time, and you are done!

So why is there so much confusion! It's because, like most things, especially in cooking, what "works all the time" is usually a pretty big simplification. But it's accurate enough for almost all cooks, especially home cooks that don't have to deal with a HACCP plan.

Weird Things Happen When Meat Heats

But for fun, let's look at all the weird stuff that is going on that tends to confuse people.

All this weird and nuanced stuff is where people tend to go down rabbit holes on social media arguing with each other and trying to sound smart about stuff that really doesn't matter much to the poor parent that just wanted to know how long to cook their dinner for!

So while we cover this, remember that all you really need to know is what we've already discussed - measure it, look it up, and cook it. For tender foods thickness equals time...and now onto the weirdness!

Ending Temperature Doesn't Affect Cook Times When Just Heating Food

The first thing you might notice is that there is no mention of the temperature you are heating your food to. We have the shape of the food, if it was frozen, but nothing about the final temperature.

And that's because it just doesn't matter.

Weird, right?

If you are going to 120°F or 130°F or 140°F it's all the same.

I don't know how universal this is across all possible temperatures from absolute zero to the center of the sun, but if you take the teeeeeeny range that we use for sous vide, it all behaves the same. So for heating meat you don't have to worry about the ending temperature.

That said, as I mentioned earlier we are concerned with goal #1, heating food through. Once we start talking about goal #2, making that food safe through pasteurization, then the end temperature does matter.

And that's because high temperatures pasteurize faster...but they still heat through at the same rate, which leads to some interesting timing.

You Can Fully Pasteurize Meat BEFORE it is Heated Through

So this 1" thick timing also generally applies to a chicken breast, and it will also heat through in an hour and 15 minutes. But now because we want to pasteurize it we have to throw the temperature into the mix.

So remember this hour and 15 minute time while we switch to the chicken pasteurization times.

So here we have the same 1" thickness of the meat that heats through in an hour and 15 minutes.

But if you are cooking it at 137°F it will take 2 hours and 15 minutes to pasteurize it. So a full hour after it's been heated through. If you just heat it through it will NOT be safe to eat. It's still got a lot of bad stuff living on it and needs that extra hour until it's safe.

But If you bump that temperature up to 145°F then due to the hotter temperature it WILL be pasteurized and safe after that hour and 15 minutes.

So the heating through and pasteurization times converge at that point, but only for that thickness.

But get ready for more weirdness... if you bump the temperature up to 149°F, it'll be safe to eat... after 55 minutes... even though it's not heated through all the way through!

Awesome, right?

And that's because once the middle of that chicken got to the 130°F to 135°F range the pasteurization process started, and it completed while the chicken was still on it's way up to the final temperature of 149°F.

Starting Temperature DOES Matter if it is Below Freezing

Now, on the other side, the starting temperature DOES matter!

But this only holds true if the food is frozen!

And that's because in physics, weird stuff happens when something goes from frozen to liquid, so those times are a lot different, but the end temperature doesn't matter.

So let's compare times.

Looking at frozen, it adds about 50% to the cook times.

• A 1/2" thick steak takes about 40 minutes instead of 30.
• A 1" thick takes almost 2 hours instead of an hour and 15 minutes
• A 2" thick steak takes 5 and a half hours instead of 3 and a half

Again, the thicker the food, the more of an impact cooking from frozen has, but a good rule of thumb is to add 50% more time to the cooking time.

So now you can easily cook your sous vide steaks from frozen...just don't tell Chef David Pietranczyk.

The next thing is, these look like exact times, right? But they are not.

None of These Numbers Are Exact

It's so important to remember these are estimates. Depending on the exact piece of meat you have, the circulation in your bath, the hardness of your water, and the fat content of the meat it can all affect the heating times. The truly exact times depend on "thermal diffusivity", a "heat transfer coefficient", the density of the food and specific heats of all the elements involved.

Now, none of this really matters to a normal cook, but some people love to talk and argue about it.

So if you see a sous vide heating chart that recommends 55 minutes, don't hold it as gospel, just know it's a good rule of thumb and should be used as a minimum time.

Because remember, this is sous vide! You have a wide range of time before your food gets over tenderized so the exact timing rarely matters!

Sure, if you take the amazing CREA class with AJ and Bruno so you can make 3-star Michelin meals then you might want to be pretty dang exact...

But for the rest of us, don't stress!

Sure, that 1" thick strip steak heats through in 75 minutes, but it's still amazing after 3 hours!

Oh, and if you were cooking above 130°F, then after 3 hours that strip steak is also pasteurized and safe to eat for anyone with a weakened immune system...even if it was from Costco and blade tenderized!

Also, a little bit of tenderization from sous vide, even for tender cuts, can be a great thing! Sure, you can just heat a sirloin steak or strip steak through, but another 3 to 5 hours tenderizes just enough that I enjoy it even more.

So this "to the minute" accuracy people are so concerned about rarely matters to most cooks.

Food Bloggers Are Not Scientists

Also, I am not writing a scientific article!

Neither are most food writers! We are cooks! This seems to come to a shock to a lot of critics but we are simply trying to help people make great food.

So yeah, I error on going a tad too long or a tad too hot, for safety. I use rounded numbers to make it a little easier on you. I generalize the science so people don't get confused with things that really don't matter for making great food.

My charts and rulers and articles are guides to help you make amazing food. If you follow them, your food will be incredible. If you use them as data in your college physics course you are going to FAIL!

So if you want to argue with me that my time is off by 38 seconds or my degree conversion isn't exact, then great, have a blast, but my response will be "It just doesn't matter to most cooks".

So don't stress about it.

Almost All Sous Vide Charts Are 1°F Less

Also, one thing that most people forget is that these charts are actually the time it takes to heat to 1°F less than your water bath temperature.

Which is why I love when people are arguing about a degree or two in the doneness of their steaks while quoting these charts in the same breath...they are almost always arguing against themselves.

But why is this true? Why do these charts go to 1°F less? I think it's so fascinating.

It is because the rate at which meat heats is actually not uniform.

We often think of meat heating like this: if it takes 2 hours to heat through, then after an hour it's halfway heated, right? But the reality is that it heats on a curve.

In a two hour cook, after an hour the meat is really about 80% of the way heated. This blew my mind when I learned it at the CREA course. It's so counter intuitive to what I thought.

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To highlight this for you all I measured a 2.5 thick piece of meat, so a big honkin' one, and put in the bath with a probe in it.

The charts say it should take about about 5 hours and 10 minutes to heat all the way through.

Here's the graph of the actual temperature over time, and the data for the last 3 hours of the cook.

I was pretty happy that it took 4 hours and 57 minutes, so pretty dang close to what my charts said. My guess is most of the difference was because my probe wasn't exactly in the middle of the meat.

But look at this data...of those 5 hours a full hour of it was going from 130°F to 131°F.

And 25 minutes going from 129°F to 130°F.

That means if you were happy with a 129°F steak you could have pulled it out of the bath in 3 and a half hours instead of 5! That's an entire hour and a half you just shaved off your cooking time.

The last 2 hours of cooking only raised the temperature 5°.

In comparison, the first 2 hours of cooking raised the core temperature 70°F. So 2 hours in the cook we were already at 114°F, which is 80% of the way to our final temperature.

So as you get closer and closer to the target temperature the heating process gets slower and slower and slower.

I think it's Modernist Cuisine that theorizes that due to ambient heat loss the core of the food NEVER gets up to the temperature of the water bath...our thermometers just aren't exact enough so they eventually give up and round it off. Dang lazy thermometers!

This is also why that chicken breast we pasteurized earlier only took 55 minutes to be safe, even though it hadn't heated through. It got up into the 140°F range pretty dang quickly and chicken only needs to be held in that range for like 10 to 20 minutes to be safe to heat.

Delta-T Cooking Explained

So this is all well and good, but where can this weirdness apply to you?

Delta-T cooking.

What is Delta-T Cooking?

Taking advantage of this difference in heating times is where the phrase Delta-T cooking comes from.

What it basically boils down to is that you set the temperature of the water bath above what you want your food to come out at, which greatly accelerates the cooking process.

At the most basic, maybe you like your steaks at medium-rare, but instead of setting it at 131°F you set it at 132°F, 1°F difference and your steak will be done 15 to 20% faster.

And most people would never be able to tell the difference in the parts of the meat that got up to 132°F instead of 131°F, so there's no loss in quality.

Delta-T Speeds Up Your Sous Vide Times

Here are a few other temps that are easy to do at home. And again, these are estimated time saving, if you want to be 100% exact or have a HACCP plan then a probe is required, but most home cooks will be fine estimating it.

So setting it 2°F over reduces the cooking time about 25 to 30%.

At 4°F you are now reducing it by 30 to 40%.

I think at 4°F you are right on the edge of where people might be able to tell a slight difference in the doneness, especially in a side-by-side test, but the meat will still come out as expected.

Above 4°F though your time savings are much smaller and the difference becomes much more noticeable if your timing isn't spot on, so I don't recommend going above this without a probe.

But at the most complex level, you can start to use a probe to monitor the core temperature. Some devices like the Anova Precision Oven and the PolyScience HydroPro Plus have built in probes and cooking programs that can set the bath temperature 10 to 20 to 30 degrees higher until the core nears the temperature then they automatically reduce the oven or water temperature so it doesn't overcook most of the food.

Once you sear the outside, the little temperature difference is still not noticeable but you can shave 50% to 60% off the cook times doing that.

As I said, for that advanced Delta-T cooking you really need a probe, and Chef David Pietranczyk actually has a great article about doing that, but for a 1 to 4°F difference you can pretty easily wing it and knock off the amount of time needed, greatly speeding up your food prep.

Delta-T Speeds Up Reheating Times!

These time reductions also actually come into play for reheating food!

Most food doesn't have to be served at the cooking temperature, so if you've already cooked your steak to 135°F you can then chill it. You can set the circulator to 135°F for reheating but pull it at the halfway mark of the timing, knowing that the core will be within about 10°F, more than hot enough to serve it.

It helps you to shave off the times that we have on our Sous Vide Timing Ruler

Conclusion

So now you know how long to cook a steak, lamb chop, pork chop or piece of fish for...and even pasteurize chicken and poultry!

Measure the thickness, look it up in a chart, and you're ready to go!

And you also know all the science and nuances that everyone else is arguing about while you're enjoying your perfectly cooked meal!

For more on the details of sous vide cooking, please check out my free sous vide quick start class or any of my favorite sous vide cookbooks.

If you like this you can get more than 85 inspiring recipes to get you on your way to sous vide success. It's all in my best selling book Modernist Cooking Made Easy: Sous Vide - Get Your Copy Today!

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This article is by me, Jason Logsdon. I'm an adventurous home cook and professional blogger who loves to try new things, especially when it comes to cooking. I've explored everything from sous vide and whipping siphons to pressure cookers and blow torches; created foams, gels and spheres; made barrel aged cocktails and brewed beer. I have also written 10 cookbooks on modernist cooking and sous vide and I run the AmazingFoodMadeEasy.com website.

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