Mexican Quick Pickled Red Onions

This is a pretty simple recipe, so there's not much need for detailed notes here. The biggest factor is generally going to be the availability of bitter orange juice, so I'll deal with that first and foremost.

I love bitter oranges and I use them as much as I can. I've even written an extensive guide to them here on the site, so I'd encourage you to check that out if you're new to the topic.

First of all, let me address what these oranges are so that we can avoid any confusion.  Bitter oranges (also called Seville, sour, marmalade, or bigarade oranges) look and smell a lot like their sweet, cousins, but they are decidedly NOT sweet.  Bitter oranges have actually been around a lot longer than sweet oranges, and while they've been eclipsed in many ways by their more fructose-friendly relatives, they still hold a prominent position in a number of cuisines and recipes around the world.  The fragrant, sour, bitter, somewhat herbal juice is particularly important in the Yucatan peninsula of Mexico, where it's used in a variety of recipes, including pickles, salsas, and the ever-popular pork dish known as puerco (or cochinita) pibil.  I personally think that bitter oranges are a deeply underappreciated ingredient, and if you can get a hold of some, I hope you'll give them a try.  They make amazing contributions to both savoury and sweet dishes; marmalade simply wouldn't be the same without the peels of bitter oranges, and one of my absolute favourite desserts is made with a mixture of lemon and Seville orange juice.

All that being said, I know it can be tricky to find these lovely oranges, so let's address substitutions in the next section.

Fortunately, there's a very simple substitute for Seville orange juice that requires only commonly available citrus types.  A 1:1:1 mixture of grapefruit, lime, and sweet orange juice makes a very good substitute in this recipe, and in any recipe that calls for bitter orange juice.  I will note that many modern grapefruit varieties emphasize sweetness over the more 'old-fashioned' bitter/sour components of the fruit, so you may want to adjust the ratio slightly with a bit of extra lime juice if you find it too sweet.  Pink grapefruit is nice for colour, but I find many of the white varieties are a little more bitter/herbal, and better suited to use in this mixture.

It's important to note that sweet oranges alone do NOT make a good substitute for Seville oranges.  While they certainly have a similar orange-like fragrance, the juice is far sweeter, and lacks the acid tang and bitterness of Seville oranges.

So what can you do if you only have sweet oranges available? Well, fortunately you're not out of luck.  The recipe can be modified by reducing the amount of orange juice to about 1/3 cup, and increasing the amount of vinegar from 1 tbsp to approximately 1/2 cup.  This doesn't produce identical results, but it still makes for a great pickle with some of the citrusy punch of the original.  I would recommend using white wine vinegar if you do go this route, as I find pure white vinegar a little too sharp and overpowering when used in such large quantities.

No citrus available? No worries, my friend. Check out my recipe for fish tacos with white-wine pickled onions.  Those onions are very similar to these, but with a different flavour profile thanks to the use of wine and wine vinegar.

Yep! No editing trickery here folks, these pickles really do come out a vibrant pink colour.  The chemical compounds that give red onions their beautiful colour are called anthocyanins.  These compounds are weakly acidic on their own, and react with acids and bases in ways that produce variations in colour.  In acidic environments (for example, a mixture of vinegar and citrus juice), the anthocyanins grab a hold of hydrogen ions (a process called protonation), and in this state they produce an intense red colour.  That red leaches into the white cells of the onions, producing the brilliant magenta colour you see in the pictures.  Similar reactions can be found in a variety of other anthocyanin-loaded foods too; purple cabbage, for example, is often used for simple DIY acid-base indicator experiments at home or in classrooms.

The food photographer side of me has a hard time imagining these pickles in a more subdued palate, but you can swap out red onions for sweet white ones (e.g. Walla Walla onions).  The resulting pickle will be similar in taste, though obviously lacking the bright colour of the original recipe.