In essence, the idea is to save vegetable peelings and ends and use them to make delicious broths ‘for free’. We started doing this while locked down at home in 2020, and at a time when we were thinking about frugality, excess, and our planetary footprint, it seemed like an excellent idea. The very first time we tried it, we were wowed by what could be made of so little. And since then it’s become a regular part of our everyday cooking.
The foundation of this broth is onion skins – that’s how it gets such a deep, rich colour. Start collecting all the vegetable bits and bobs, seal in airtight containers, and freeze until you’re ready to make the broth. A basic vegetable broth is just a very diluted soffritto, so take your cue from that. Save carrot peelings, the heart and leaves of a bunch of celery, some parsley, perhaps a leek – and, of course, the onion skins.
This broth is defined by a brilliant clarity and rich brown colour with sweet, vegetal, and savoury flavours.
The magic tricks
Rich brown: onion skins are the magic ingredient for a deep bronze colour. The trick is to leave them in just long enough to benefit the colour without negatively affecting flavour.
Clarity: gentle cooking for a maximum of 30 minutes.
Savoury: roasting intensifies flavour. For savoury depth add mushrooms. And if, like us, you are a Marmite fiend, save the empty jars and when making stock fill with freshly boiled water, shake up to get all the marmite off the sides and add to your stock. (This will also turn the stock slightly darker.)
The method
Whenever you’re prepping veggies, gather up the peelings and trimmings from the chopping board, pop them in an airtight container, and keep in the freezer until you’re ready to make stock.
In general use whatever you have. This might include a couple of handfuls of skins and ends of onions together with the peels and ends of carrots, a celery heart or leaves, the green tops and tails of some big leeks or some spring onions.
And since it’s a great way to use things that are a little ‘sad’, that may include a rogue onion that’s started to sprout, a floppy fistful of parsley and a lone carrot that’s escaped capture for quite some time.
There is no rule for quantity, because the more you have, the more flavourful the stock will be, depending on the size of the pot you use and the amount of water. Just follow your nose. For a really big stock pot, the kind you’d use for boiling pasta, you want about four or five cups worth of veggie matter.
The first thing to do is to spread all of your trimmings around on a baking tray and put it into an oven preheated to 150°C (on the middle rack). You need to keep an eye on things and mix it up every 15 minutes or so, but after about 45 minutes, the mass should have noticeably shrunk and there might be edges that are browned and roasty. The idea is simply to ‘steam’ off some of the moisture in the vegetables and concentrate the flavours.
At this stage, you could just use the roasted offerings to make stock, but to take it to the next level I always add:
a bay leaf or two
5 or 6 peppercorns and, if you can find them, 3 or 4 juniper berries.
a few chopped mushrooms. If you have the time and inclination, fry them off first for an added burst of shroominess.
a star anise. Optional: I like what this flavour brings, Nikki thinks it can come over a bit strong.
Now all you need to do is remove any blackened or burnt bits from the baking tray and discard. Chop everything up roughly, put it in a big pot, cover with water, add the remaining ingredients and the spices, bring to the boil, then turn down to a simmer and wait. Stir occasionally and remove any scum from the top.
Very importantly, after about 10 minutes, fish out as many onion skins as you can. They are great for adding colour, but if you leave them in too long, they tend to impart a bitterness that isn’t pleasant.
At around 15 minutes, taste to make sure the star anise isn’t trying to take over the party completely. This will depend on the freshness of the spice. It should leave just a hint of perfume. If it’s not overpowering, leave it in for as long as you feel appropriate.
After 25 to 30 minutes, most of the goodness will be extracted. The longer you go, the more chance there is of it turning bitter, so call a halt to proceedings earlier rather than later.
Strain the stock through a sieve, preferably lined with fine cheesecloth, and return to the stove top. (This is when you can add your Marmite water!) Turn up the gas and boil away until you’ve got the intensity you want. Then season with enough salt to bring out and round off the flavour.
The rules of thumb
What to use
When you think about it, a basic vegetable stock is just a very diluted soffritto, so onion, carrot, and celery are always going to work. But we’ve also had good results with all sorts of things like squash and pumpkin bits. Use common sense when it comes to very strongly flavoured things like chillies. And in general, stalks are always better than leaves.
What not to use
The brassica family. Just leave them alone. We’re talking broccoli and cauliflower, cabbage, kale, kohlrabi and even turnips.
Considering colour
Chard leaves will turn a stock really dark and avoid anything beetroot. But pumpkin flesh lends a golden quality to the onion-skin hue.
Timing
We’ve already said it, but it’s worth repeating: if you leave it on the heat for too long, it can become bitter and that will ruin your stock. Rather extract less in the simmer and concentrate the flavour by boiling down the stock.