Mahi Mahi al Pil Pil

I think we may have broken new ground here: the classic Basque Pil Pil sauce is always made with bacalao -- salt cod. We repeated the modern poaching-in-olive-oil technique that we used recently, but this time for mahi mahi. It rendered a lower quantity of the gelatin required to make this wonderful emulsified sauce than bacalao, but it was plenty to sauce the fish: like bacalao, the fish -- along with good olive oil -- produced its own hollandaise/mayonnaise-like sauce, super rich. In tonight's experiment, we also tried a sea trout because it had a thick subcutaneous layer of fat, but it didn't render the gelatin like bacalao does, so it could not make its own sauce.

Mahi Mahi and Sea Trout with Pil Pil sauce, shishito peppers, potatoes

We reasoned that a cold-water fish with a layer of fat would work like cod, from which bacalao is made, so we got sea trout (150g); it looks very much like salmon.  We also wanted to try a warm-water fish like we find when we visit Florida, so we got mahi mahi (270g). The quantities don't really matter here, the technique does.

We put each fish in its own small pan, skin side up (the skin sticks if it's touching the bottom), and covered with tasty extra virgin oil; we added a couple cloves of garlic to each. Heat up each to poach the fish, and hopefully release some precious gelatin which will act as an emulsifier.  Keep the oil well below boiling of water so you don't evaporate off any rendered gelatin. The trout released no gelatin, but the mahi mahi seemed to release a little.  The oil was about 90C/194F.

We pulled the trout out after about 15 minutes, but the mahi mahi is a more dense fish so we left it for about 30 minutes. Our theory is that the gelatin comes from just under the skin, so we pulled off the skin and added it back to the hot oil to cook another 10 minutes. We strained the oil into a measuring cup and let it settle, and after another 10 minutes or so were delighted to see oil on top and something that looked like heavier, water-based gelatin on the bottom. I separated most of the oil off and poured the gelatin portion into a tall narrow glass to separate further.

Oil on the top, gelatin on the bottom

I slurped the bottom layer of what we optimistically assumed was gelatin with a turkey baster and transferred it into a cool skillet. I then whipped this a few minutes with a fine mesh strainer to beat air into it and was very happy to see a foam form, the precursor to an emulsion. I added some of the now-cooled oil little by little to establish the emulsified sauce.

Whipping the gelatin until a white foam is established

It seemed more thin than the bacalao-based emulsion but I kept adding oil and it built up nicely. I had the heat on as low as it can go on my cooktop, but I'm not sure I needed any heat at all -- I think too much heat would cause the sauce to break.

Add the fishy oil little by little at first, more aggressively when the sauce is established

Once well-established I could add more oil with impunity. This 19 second video should show the sauce coming together.

The sauce was rich with olive oil flavor, a fine quality oil pays off here since it's really the only ingredient.   It wasn't seasoned with anything, so when we plated, we added some salt and a squeeze of fresh lemon juice.

What did we learn?

I've not seen recipes for pil pil using anything than bacalao. There are "shrimp pil pil" or "gambas al pil pil" but these are really shrimp in oil with garlic and hot chili pepper: "gambas al ajillo" and not an emulsified sauce at all.

Bacalao isn't the only fish from which gelatin can be extracted to use as an emulsifier for pil pil sauce. but not all fish will release gelatin. We have no idea which will and which won't, but mahi mahi definitely will. 

Next Steps

We'd like to repeat the experiment with the easier-to-find dried bacalao, the kind that's as hard as a sheet of plywood, and encrusted in salt. This is the classic form, and has to be hydrated with fresh water for a couple days. It has skin, and usually has bones which we're hope will be easy to remove once poached.  This is the baseline that all other work should really start from, and we're quite certain that will work fine.

Can we cook the bacalao with a minimum amount of olive oil using a sous vide technique? Use only the amount of oil you'd need for the sauce, maybe 200 ml, not the pots full we need for poaching. Freeze the olive oil solid (so it doesn't squirt out) and place in a vacuum bag with the hydrated bacalao and a couple cloves of garlic. Cook at the same 90C/195F for 30 minutes or so and check for rendered gelatin.

If sous vide works, can we use a lower, fish-friendly temperature, e.g., 50C/125F instead of the 90C/195F we used today?  We could hold the fish almost indefinitely without fear of over cooking, as long as we need to render gelatin.

Can we get gelatin from skinless, boneless bacalao that's now showing up in regular gringo grocery stores? This would make it much more accessible.

Can we season the sauce as we're building the emulsion? Salt seems easy, since salt cod's full of it. Can we add some lemon juice or white wine, or would those denature the gelatin and ruin the sauce?

Is the garlic important? In old school Catalan and Provençal aioli, garlic is the emulsifier. It's a very difficult sauce to make as it's a weak emulsifier and it breaks in the blink of an eye. Once we've established above what works with garlic, does the quality suffer without the garlic?