We're reader-supported. If you buy through our links, we may earn a commission at no cost to you.

Do You Simmer With the Lid On Or Off To Thicken?

Whether you’re trying to thicken up a luscious leek and cider sauce, reduce a tongue-tastic red wine jus, or make a rich and robust gravy, the absolute best way to do it is to go lidless. That’s right, friends. Pop your tops!

Searing with the lid on keeps the moisture in. The cooking liquid in your pot still turns to steam, but that team gets trapped by the lid and, as it cools, turns into water and drips back into the soup or stew.

In light of this, simmering with the lid on is a godsend when you’re cooking ingredients directly in the sauce, and you don’t want to reduce it too much. But it’s not ideal for when you want it to thicken.

To reinforce that sauce, remove the pot’s lid, set it to one side, and let the steam rise freely into the air. We’d crack a window or turn on an extraction fan if you have one, otherwise, you’ll have a real Titanic situation on your hands—you know which scene we mean.

Once a certain amount of moisture is out of the equation, you should notice that your sauce is adhering more to ingredients, and it’s not as watery.

When you simmer with the lid off, you’re not just altering the consistency of your sauce, you’re concentrating the flavor, ensuring it packs as much of a punch as humanly possible.

Reducing a liquid such as wine, juice, or stock in a pan before the rest of the ingredients are added follows the same principles. Leave that lid in the cupboard, and let the moisture cook off. You should be able to see the original level of the liquid faintly on the wall of the pan.

You can use this to help judge how much longer the reduction will take.

Remember to stir frequently, especially if you’re using an unseasoned pan. The last thing you want is for your sauce to catch, as the burnt flavor will pass into the meal at large, ruining your hard work and wasting all your lovely ingredients.

Although reducing and thickening are done for different purposes and at different stages in the cooking process, the physics of the process is exactly the same. After you’ve hit it with a spot of controlled evaporation, your sauce isn’t just thickening, it’s losing mass.

You’ll need to account for this saucy shrinkage before you start thickening, otherwise, you may end up with a beautifully full and flavorful final product that simply doesn’t stretch far enough.

What to Do When You’ve Thickened the Sauce Too Much

However, try not to panic if you’ve ‘Honey, I’ve shrunk the sauce’-ed your meal, as there are ways to bring its volume back up. 

Adding water is the easiest option. It will dilute your super concentrated flavors a little, but the benefit is that it doesn’t muddy the meal with its own flavor.

If you’re working on a creamy sauce, a drizzle of cream or perhaps a spill of white wine will do the trick, but unlike water, these ingredients have a distinct taste.

Adding more into your food is going to change the flavor profile, so in this scenario, it’s best to pour with great care and keep tasting your sauce as you go.

As pot lids have a small hole in them to equalize the pressure, if you kept it on, eventually enough moisture would escape, thickening your sauce, but it would take a really long time, and you run the risk of overcooking your food.

Do bear in mind; however, that even without a lid, reducing a sauce the au naturale way takes time, especially if it was exceedingly thin to begin with. Evaporation is a gradual process, so if you’re stuck in a time-sensitive situation, it’s good to have a backup.

The best alternative to thickening liquids over time is to use a pinch of cornflour. It’s fast, effective, and completely gluten-free—hurrah! Simply scoop a couple of teaspoons (tablespoons if you’re cooking for the masses), into a jug, and stir in a sprinkle of fresh, cold water.

You don’t want to use too much water as it will dilute the flavor of your sauce. You only need enough to give the cornflour the consistency of a loose paste. Now you’re ready to get thick, but wait!

Before you stir in your miracle thickening tonic, you need to make sure your soon-to-be delicious sauce is bubbling away. If you add your cornflour and water concoction to a cool pot, the flour won’t cook into the sauce, and it won’t thicken.

Once you can see the bubbles a-risin’ in your saucepan, you can gradually tip your cornflour in, stirring as you go. Within seconds, you should feel more resistance against your stirring utensil. This is your sauce thickening at breakneck speed before your eyes—amazing, right?

Don’t worry if you don’t have any cornflour to hand, because we have another quick thickening fix you can use when you find yourself in a tricky situation.

What is it, you ask? Well, it’s nothing special, we’re afraid, just good old-fashioned plain flour. That’s it, culinary chums; the answer was under your noses the whole time.

It’s no good going hell for leather with the plain flour in your painstakingly concocted sauce, though—we found that out the hard way.  The thing about plain flour is that it tends to clump, forming infuriating little lumps that are impossible to stir into your sauce.

So, unless you’re planning to blitz your sauce with an immersion blender or pass the whole thing through a sieve, give adding flour directly a miss.

Instead, grab that sieve, sprinkle some plain flour into it, then gently tap some powdered flour into your sauce, stirring it in as you go. It’s not quite as fast-acting as cornflour, but stick with it, adding the flour in increments and stirring until you reach the desired viscosity.

Butter is another fantastic way to thicken up something like a soup or, say, a beef broth. Simply simmer until it reduces around a centimeter, then add a knob to a small stick of butter depending on the size of the meal.

Be wary though, adding fats into a sauce too quickly will cause it to split.