How many of you grew up with the phrase “fish is cooked in lemon”? There are a lot of home cooks in my family, so I’ve heard for my entire life that cooking fish with heat wasn’t actually necessary because it could be done with lemon.
Frankly, I never questioned that theory until one day when I was in culinary school we were talking about cooking methods and the chef never mentioned lemon. At that moment I started asking myself how it was possible that no one around me ever stopped for a second and asked themselves if that theory was actually true! Of course this teaching was passed down generation after generation, so who in their right mind would question the great granny about that?
So if you’re one of those people who were taught that fish could be cooked in lemon, you’re in the right place. The answer for that unsettling question is no. Simply because to be able to use the word “cooked” that means you’d have to elevate that food’s temperature until its organoleptic properties (color, smell, taste and texture) are changed and it becomes digestible.
The saying that fish can be cooked in lemon juice has been incorrectly used for so long because when you leave fish resting in lemon juice for a period of time, it changes its texture and color. This doesn’t mean that it actually cooked, solely the lemon’s citric acid is reacting with the fish’s protein causing it to denature and to change its properties. Denaturation happens when a protein of animal origin comes in contact with a citric whose pH is less than 4.8.
This process also happens when the protein is exposed to heat. That's why we can encounter proteins that are often submerged in lemon juice for a certain time and then cooked. What happens is that this protein will require less cooking time than the protein that wasn’t submerged in lemon beforehand.
Now, you’re most likely wondering… if fish isn’t cooked in lemon, then what does it do? Well, it just marinades, since what we are doing is simply submerging a protein in a liquid for a certain period of time making the protein taste better.
Something very important to lay stress on is that this food would be eaten raw. There are several dishes that are served like that, such as ceviche, aguachile and steak tartar. Nonetheless, proteins like chicken should never be eaten like this, since the citric acid isn’t strong enough to kill certain microorganisms that could be potentially dangerous for humans. We must remember that chicken shouldn’t be ingested if its internal temperature hasn’t reached 165°F (75°C).
To make sure that your proteins are as clean as possible for your ceviche, make sure to buy the protein in large pieces and cut it yourself to your desired size at home. Also, try not to break the protein’s cold chain, this means that it should go straight from the supermarket’s freezer to your home’s fridge. Try to eat it that same day. Last but not least, make sure the place where you are buying your proteins from, is high quality, clean and hygienic.
Now you know, next time that someone says that fish is cooked in lemon, you’ll be able to explain that it is in fact not cooked, but marinated.