Halibut Escabeche

This is a subject that can be simple or complex, depending how deep you want to go. Basically, foods go bad because of a combination of internal factors (enzymes and other compounds that break down a food from within), and external factors (bacteria, fungi, the rat that bit one of my cucumbers on the vine last year, etc). Internal factors are particularly common in fruits and vegetables - an apple WANTS to rot and fall apart so that its seeds can get to the ground. External factors are common in all kinds of foods, primarily because bacteria and fungi want to eat your food just as much as you do. Food processing aims to stop or slow these factors.

Cooking the escabeche kills a lot (but not all - never all) of the bacteria and fungi, especially on the surface of the fish. This helps to sterilize the fish. Obviously this effect is temporary - leave the cooked fish out on the counter on a bare plate and it will be re-colonized by microbes in the air, and they'll break down the food.

Cooking also inactivates enzymes like protease that might be in the fish, preventing them from breaking down the tissues of the fish itself. This factor is not so important in the short term, but fairly important in the long term.

On the opposite side of the equation, you've got the elimination of heat - a concept we're all quite familiar with now, and one which was once a significant luxury. Bacteria and fungi grow slowly in cold environments (though they obviously still grow - we've all found something fuzzy and awful at the back of the fridge). Putting cooked food in the refrigerator retards spoilage, allowing us to hang onto foods longer - if you refrigerate the escabeche before serving it, you're taking advantage of this. Ironically, the prevalence of this type of preservation is probably at least partially responsible for our uncertainty and unfamiliarity surrounding other methods. A refrigerator is easy to use, and it doesn't add any flavour to foods, unlike oils, vinegars, salts, sugars, etc.

The well-cooked fish is now a much more neutral environment. You've eliminated a bunch of the factors that would like to spoil the fish. Now we need to prevent others from showing up. The refrigerator is part of that process in the long term, but there's a lot more going on with the escabeche.

Bacteria and fungi are everywhere. That's not meant to sound scary - in fact it's fundamental to the existence of life on Earth. But as far as food preservation is concerned, the ultimate goal is to eliminate as many of these spoilage agents as possible, and prevent the remaining ones from replicating. This is important because bacteria and fungi spoil your food by succeeding. Eat, reproduce, repeat. One bacterium would never spoil your food, but logarithmic growth means that a single bacterium turns into billions over a very short period of time, and this prokaryotic collective can render  your food inedible in no time. Fungi don't work exactly the same way, but the idea is similar - grow, eat, repeat. (Hopefully the aforementioned rat isn't a problem in this setting). Heating gets rid of a lot of spoilage agents (in some cases, like pressurized canning, nearly all of them), but food preservation is largely concerned with making things very inhospitable for the remainder.

Water Activity - Like us, bacteria and fungi need water to do their thing. Water availability is measured in terms of something called 'water activity,' which is measured between 0 (absolutely no water is available) and 1 (pure, distilled water). Most bacteria require water activity of 0.91 to live, while most fungi require about 0.7. What does this mean for food? If you leave a cracker on the counter, it's probably going to be fine for a VERY long time. It has very low water activity. But get that same cracker wet (even with pure, distilled, clean water) and it will start to mold up pretty quickly. Foods with high water activity spoil faster. But the difference is not just wet vs. dry - other factors can reduce water availability too. Sugar and salt make good preservatives because they want to suck up water to such a degree that they'll draw it out of the cells of bacteria and fungi. That's why a salted piece of meat can sit out at room temperature for a year or more - the surface of the food is salted to the point of utter inhospitability. It might as well be the surface of Mars as far as bacteria are concerned.

Cooking the escabeche eliminates some of the water, while the oil (which doesn't mix with water) helps keep any additional water (e.g. in the air) away from the fish.

Acidity - Spoilage agents like to live at very specific pH ranges. Too high or low, and their metabolic processes don't work (the same is true of us incidentally). Vinegar is a very popular preservative because it creates a highly acidic environment that's extremely inhospitable to most bacteria. The vinegar in the escabeche does precisely this, in addition to adding a distinctive and pleasing sour tanginess. For what it's worth, sourness is actually a hallmark of acidic compounds.

Oxygen - Most bacteria and all fungi require oxygen for their metabolic processes. If you can eliminate oxygen from your preserved food, you can prevent a lot of spoilage. In the case of the escabeche, olive oil creates a low-oxygen environment around the fish that prevents bacterial proliferation.

While oil is great for creating low-oxygen environments, it's not enough on its own. Some bacteria live just fine without oxygen, Clostridium botulinum, the VERY dangerous species that causes botulism poisoning. The spores of this bacteria are incredibly hardy and can survive boiling temperatures, but it can't replicate in an overly salty and/or acidic environment. In the escabeche, the combination of vinegar and oil creates a one-two preservation punch.

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So now that your fears have, hopefully, been soothed by science (science is really good at both reducing AND inducing terror), let me point out a REALLY great reason to make escabeche - you cook once (and note that it only takes about 15 minutes), and you could literally eat this all week.  Pull a piece out, leave it on the counter (or microwave it for expediency) and voila.  Serve it with green rice, make tacos, add some beans - it's all good, and it's all easy.

To close I want to say one last thing about just what we're doing here: we're turning fresh food into preserved and processed food.  There's a really good chance that the word processed makes you feel spectacularly uncomfortable, but let me explain.  Fantastically fresh food is sublime; there's nothing like a strawberry fresh from the garden, or a fish filleted moments after it's been caught.  But many successful animals, ourselves included, have figured out that it's a good idea to keep some extra food around for those times where fresh food is scarce.  It behooves us to think of ways to feed ourselves not just now, but tomorrow, next week, or next year.  When we cook, can, pickle, smoke, freeze, ferment, dry, or otherwise preserve and/or modify our food, we are processing it.  It's bizarre to think of our food that way but it's true.  The problem is not the word 'processed,' it's the quality of the food going in, and the end-goal of the processor.

Escabeche isn't crazy. It's just a different way of thinking about food - in fact, it's an older way of thinking. True, it still uses the refrigerator to stay safe for a week (or more - I'm actually being conservative). But the other processing and preservation methods actually make it shockingly stable even at warm temperatures - after all, this recipe is originally from Mexico.  It's simply an example of how we can apply scientific principles to create great food that also happens to be rather enduring.  Sadly, many of us are more familiar with these principles as they are applied to some spectacularly unhealthy foods, and that really needs to start changing.  When I put up 12 jars of pickled peppers in the Fall, I'm making preserved, processed food.  And that's not a bad thing.  Instead of recoiling when we hear the p-words, it's time to reclaim them and differentiate them from the industrial processes used to sell us heavily modified, nutritionally poor, environmentally questionable 'food.'  Processed and preserved food can be good, even great food - especially when you're the one in charge.