Russ Parsons: Are caramelised onions the peak of human endeavour? They’re up there

Making this amazing building block to flavour takes time, but you’ll end up with edible gold

Ancient alchemists sought without success to turn base metals into gold. I think I have done it. Granted, it’s a bit harsh to call the ever-so-useful brown onion a base metal, no matter how common or inexpensive they may be. But I don’t think it’s going too far to call caramelised onions culinary gold.

All it takes to create this magic is a good heavy pot and a lot of time. When you’re done, you’ve got an ingredient with such a deep savoury flavour and buttery texture that you’ll want to have a jar of it in your refrigerator at all times. Spread it on a pizza or a toastie, layer it in a gratin, use it as a base for all kinds of sauces, soups and stews – even spread it on steaks as a kind of onion jam. All it takes is a tablespoon or two to transform a dish.

Now you may have seen recipe references to “caramelised onions” that can be accomplished in five to 10 minutes. These are not those. In fact, those are not truly caramelised at all, but at best lightly browned.

True caramelisation is a chemical process in which simple sugars are cooked to a high enough temperature that they break down and reform into complex, sweet, buttery flavours. Combine that with a trace of onions’ native burn and you’ve got something special.

In outline, these caramelised onions couldn’t be simpler to make: slice onions, put them in a pot, cook them over low temperature until they turn a deep brown the colour of oak or even mahogany.

And in truth, that’s pretty much all there is to it. But the process does take careful minding. Too high a heat, or if you leave the onions too long without stirring, you risk scorching. At which point they turn so penetratingly bitter the only thing to do is throw the whole thing out, wipe the pot clean and start over.

So take your time and pay attention. Back in Los Angeles, caramelising onions was always a rainy day project for me. Which meant I made them only a couple of times a year. Here in Ireland, we've got no excuse for not having a fridge full.

Start with a one kilogramme bag of regular brown onions – the cheapest ones at the grocery. Top, tail and trim them, then slice them roughly one centimetre thick (much thinner and the risk of scorching increases).

Dump them into the heaviest stew pot you have and add a sprinkle of salt and a splash of oil. Cover and put it over medium-low heat to start the cooking, stirring every 10 minutes. After about 30 minutes, the onions will start to soften. Another 30 minutes and they should be velvety and positively swimming in liquid.

Grab a book

At this point remove the lid, turn the heat down as low as it will go and, stirring frequently, wait patiently for the liquid to evaporate so the caramelising can begin (this starts at about 110 degrees, so almost all of the water has to be cooked away).

Do your laundry or read a good book (I heartily recommend Luke Cassidy’s Iron Annie – not only is it beautifully written, but the chapters are just about the perfect length to remind you to stir every 10 minutes).

After another 30 minutes or so, the liquid will begin to disappear. The onion mixture will feel thicker when you stir it and the colour will very subtly start to darken. Keep going slowly.

Eventually, after about 2½ hours, the onions will be noticeably drier, the consistency of marmalade, and the colour will be a deep khaki, with flecks of mahogany beginning to appear. Careful now. Gradually the colour will darken further. Keep stirring and watch carefully. With so much of the liquid evaporated, the onions will want to stick and scorch.

Finally, after about 3½ hours, the colour should be deep enough to think about stopping. The colour will be a reddish-brown and if you listen carefully you’ll hear the onions sizzling as they fry. How much further to push them will depend on how brave you are. Improvement in flavour from this point is incremental, but the risk of burning and ruining increases dramatically.

My initial kilo sack of onions cooked down to a little less than a cup of onion jam. Covered tightly, this will sit in my refrigerator for several weeks – theoretically at least. Even using it just a couple of tablespoons at a time I find that it disappears quickly.

Thank goodness we have no shortage of rainy days fit for cooking.

THE ONION IS TRULY A MULTILAYERED MARVEL

If ever there was an example of a miracle hiding in plain sight, it is the onion. We rarely give it a second thought, yet it is a marvel of chemistry. Have you ever wondered why a raw onion is hard as a sliotar, but cooks away to satiny ribbons? Why a whole onion has a very mild smell, yet as soon as you cut it is so acrid that it makes you cry?

The basic brown storage onion is about 90 per cent water, held in tight little packets under such pressure that it feels hard as a rock. Think of a balloon inflated to the point just before it pops. When an onion is cooked, the water expands, bursting out of the packets and leaving behind just a thin vegetable skin.

Mixed with all of that water is a complex assortment of chemical components. When an onion is cut, those chemicals combine and recombine to form new compounds, one of which is a near relative of sulphuric acid.

One onion scientist (yes, there is such a thing) waxed poetic, telling me it is “a cascade of chemical reactions that occur in the blink of an eye”. The result is so volatile that, even at room temperature, it evaporates into the air – usually winding up right up your nose and in your eyes, which causes the famous onion ugly crying.

There are many folk tales about how to avoid onion tears, but if you follow the science, there are only a couple of things that will help. Chilling the onion will reduce the risk. But the most effective way is simply making sure your knife is extremely sharp – that way it slices through narrow band of cells rather than crushing a broad swathe.

Want to lessen the bite of raw onions in a salad? Rinsing the slices in ice-cold water will remove most of the acid. And soaking them in a bit of vinegar will offset the natural bite, making them seem sweeter.

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