Today is the first day of the 2021 Sous Vide Summit, and I am one of Friday’s speakers. My presentation will be a summary of the blog post below.
For me there is no ‘right’ and ‘wrong’ when it comes to cooking and food blogging. It is not about following rules, it is about getting the results you want. This is why in my recipes I do not only tell you what to do, but also explain why a step or technique works. I try to make a strict distinction between facts and personal preference. For example, it is a fact that a steak will be well done if you cook it to a core temperature of 70 Celsius or 160 Fahrenheit. It is my personal opinion that means ruining the steak. But it doesn’t mean that it is wrong. It would be wrong if someone would state that a steak cooked to 70 Celsius or 160 Fahrenheit is medium rare though.
There are many rules for food and cooking that are incorrect or not significant. If a rule doesn’t make sense to me or if I wonder if it is worth the extra effort, I will do experiments to find out if I can taste or measure the difference, with a detailed report on my blog. Let me give you three examples:
- I have compared pesto made in a food processor and pesto made by hand with mortar and pestle. The hand-made pesto clearly had a deeper flavor, but in practice I still use the food processor because it is just too much work to do it by hand.
- A well-known example of an outdated rule that simply isn’t true is that searing meat will seal in the juices. Searing is an important step in many recipes to add flavor, but it does not seal in the juices.
- Some people put herbs and spices in the bag when cooking sous vide, others do not. I have done experiments that confirm that the herbs and spices do not penetrate deeply into the meat, they just flavor the outside. That does not mean however that putting those herbs and spices in the bag is wrong, because they still flavor the outside of the meat and you are going to eat that outside.
I find it very convenient to have a freezer full of sous vide cooked meats, that can be defrosted and reheated sous vide in an hour or less. Frequently asked questions regarding the combination of sous vide and freezing are:
- Can I freeze meat after cooking it sous vide?
- Do I have to thaw frozen meat before cooking it sous vide?
- Do I have to thaw meat that was cooked sous vide and then frozen before reheating it sous vide?
- Is it better to freeze raw meat or to freeze it after cooking sous vide?
There are two underlying issues: the first is the effect on food safety, the second is the effect on the result, especially the juiciness of the meat.
A comprehensive article on food safety is already available on my blog, so let’s keep it brief. There are many simplified rules out there that try to make sure you won’t get sick, but not following those rules doesn’t necessarily mean that you will get sick. For instance if you allow frozen meat to thaw in the refrigerator and then immediately freeze it again, from a food safety standpoint there is hardly any risk. The only rule to follow is to make sure you don’t go beyond the shelf life in the refrigerator, and that you have to make sure that the meat doesn’t spend too much time between 5C/40F and 52C/125F. So thawing at room temperature is OK for a thin piece of meat, but not for a large piece of meat, because it would take too long. And you should not freeze it again after thawing at room temperature rather than in the refrigerator.
This article is about the effect of different combinations of freezing, sous viding and thawing on the result. Freezing does have a bad effect on the juiciness of meat. You can think of meat as a stack of balloons filled with water. The balloons are the meat cells. If the meat freezes, the ice crystals will pierce some of the balloons so they will start leaking as soon as the meat thaws again. You have probably noticed that when you thaw frozen meat, there will be a lot of juice in the bag.
Some people that respond to Facebook questions say you must do this or never do that. However, from experience I know that all combinations will result in something that is edible. What I wanted to find out is, does it actually matter? Can you taste or measure the difference?
For this experiment I decided to use chicken breast, because it is such a homogenous piece of meat. This makes it easier to draw conclusions from experiments, as there are no confounding factors that can influence the results. I am confident that my results for chicken breast will also apply for other types of meat.
Salt is an important factor for the juiciness of the meat, as I had already concluded from earlier experiments. I seasoned the chicken breast before cooking sous vide with an exact amount of 1% of salt by weight (this works out to about 1/4 teaspoon for a chicken breast half of 180 grams).
After salting I vacuum sealed the chicken breast halves, and weighed them with precision scales. I labeled each bag with the start weight and the intended order of freezing and sous vide cooking.
I cooked the chicken breast halves sous vide for 90 minutes at 60C/140F. 60 minutes would have been sufficient to pasteurize the chicken, but I opted for 90 minutes to be able to freeze after 60 minutes and then defrosting and reheating the chicken breast sous vide for another 30 minutes, thus keeping the total time the same for each experiment. There are slight differences in cooking time between the pieces, because cooking for 90 minutes from raw means that the chicken breast will spend longer at 60C/140F than when cooking from frozen. To keep the experiment simple and close to practical purposes, I did not try to correct for that. I know from another experiment that I did with chicken breast that at difference of at least a whole hour is needed to get a significant difference, so it is precise enough for this experiment.
At the end I took each chicken breast out of the bag and pat it dry with paper towels. Thus all the juices that were lost are left behind in the bag, or are absorbed by the paper towel.
Then I used the precision scales to weigh them, and calculate the amount of weight that was lost, because that indicated what portion of the juices was lost from the cooking, freezing, and defrosting. The chicken breast that was cooked sous vide for 90 minutes without any freezing or defrosting dropped from 179.92 grams to 168.73 grams, a loss of juices of (179.92 – 168.73) / 179.92 = 6.2%.
Altogether I performed more than 20 experiments with different orders and methods, such as freeze raw and then cook sous vide, or cook sous vide from raw and then freeze. I also did some experiments to establish the effect of salting before cooking sous vide.
From these experiments, it is clear that the difference between cooking salted and cooking unsalted chicken breast, is much larger than the difference between freezing or not freezing an unsalted chicken breast that has been cooked sous vide. Other than you might expect, the meat loses more juices when it is cooked unsalted. One can just taste the difference between 6.2% loss of juices for a salted chicken breast and 11.9% for an unsalted chicken breast, but the difference between 11.9% and 12.8% is too small to be tasted.
The table below lists the results for the experiments with salt:
The main finding from all these experiments is that the differences are so small, that one can hardly taste them, if at all. And that is when tasting side by side; otherwise one would probably not notice the difference at all. The loss of juices is between 5% and 13% in all experiments. Personally I can just taste the difference between 5% and 13% when tasted side by side. They are both tasty and good. I am hardly or not at all able to taste a smaller difference of 2% of 3%.
The main conclusion is therefore that it doesn’t matter so much if you freeze first and then cook sous vide, or the other way around. And neither does it matter if you defrost meat before cooking or reheating sous vide, or put it in the sous vide when still frozen. Because the differences are so small, you can just do what is most convenient. Having said that, I do have three points of advice:
- To save time, you can put meat (raw or cooked) in the sous vide without defrosting first. Defrosting will be a lot quicker that way, it is safe, and there is hardly any difference in the result.
- Frozen thin pieces of meat that has been cooked sous vide already and only needs to be pan-seared to be served, can be defrosted quickly in cold water. Frozen thick pieces of meat will not be warm enough on the inside from pan-searing only, and should be defrosted and reheated sous vide before searing.
- You can use a lower temperature to (defrost and) reheat sous vide cooked meat, as that will slightly limit the loss of juices.
At first I did not understand all of the results I was seeing. Freezing first and then cooking sous vide resulted in a slightly lower loss of juices than just cooking sous vide without freezing first, while one would expect that freezing would cause additional loss of juices. That difference became even larger when I defrosted the frozen raw chicken breast before cooking sous vide. After giving it some thought, I suspected this was caused by the salt. During the freezing (and defrosting) of the raw chicken, the salt has more time to penetrate into the meat before the cooking begins. I confirmed this suspicion by salting the chicken 8 hours before cooking sous vide. That also resulted in a lower loss of juices.
The second conclusion from these experiments is therefore that salt, and the time the salt has to penetrate the meat before sous vide cooking, are more important factors for loss of juices than freezing and defrosting.
Furthermore, it struck me that cooking in two steps (first 60 minutes and then another 30 minutes after chilling or freezing) resulted in a greater loss of juices than cooking in one step (90 minutes continuously). From my earlier experiments I thought I was seeing the effect of the freezing, but then I saw the same effect when just chilling between the two steps. I subsequently found that this effect could be eliminated by using a lower temperature of 55C/131F for the final 30 minutes of reheating instead of the original 60C/140F. I guess the loss of juices by the second step of cooking at 60C/140F is caused by ‘squeezing’ the meat for a second time.
The third conclusion of these experiments is that it is preferable to reheat sous vide cooked meat at a slightly lower temperature than it was cooked at. This does not only apply to meat that was frozen after sous vide cooking, but also for meat that was only chilled.
Because of these results that confused me initially, I had to do many more experiments for this article, than I had planned originally.
I am not saying these were scientific experiments. For instance, the chicken breasts varied somewhat in size, and the time they spent in the freezer was not exactly the same. I repeated some of the experiments, and sometimes got results that were a few percentage points apart because of such factors.
But I am confident to say that for home cooks, my experiments have clearly demonstrated that there is no need to make a big deal about whether you freeze before or after sous vide, or whether you defrost first or sous vide directly from frozen. This is because the differences are small and hard to taste, if you can taste them at all.