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How To Thicken Japanese Curry – I Test 10 Methods [Pics]

If you’re staring at a pot of watery Japanese curry – this article is for you.

I have experimented with over 10 different thickening techniques to find out what delivers the optimal consistency and taste with the least effort.

Most of these thickening techniques use ingredients you probably already own.

In a rush? Here’s the short answer.

The best way to thicken a Japanese curry is with a store-bought roux. Heat your curry sauce until it starts to simmer. Add a small amount of the store-bought roux to the curry sauce and stir until dissolved. Wait 2-3 minutes to see the thickening effect. One teaspoon thickens roughly 1 cup of sauce.

A note on my experiment

I cooked up a big batch of Japanese curry but purposefully went a little heavy-handed on the water.

The result?

A runny, watery sauce. 

Next, I tested ten different ways to thicken up the sauce.

Ten ways to thicken a Japanese curry:

  • More store-bought roux
  • A cornstarch slurry (similar to arrowroot)
  • A flour and water slurry
  • A beurre manie (a flour/butter mixture)
  • Pureed vegetables
  • Simmering the sauce for longer
  • Instant mash
  • A homemade roux (not recommended)
  • Coconut milk (not recommended)
  • Peanut butter (not recommended)

The best methods were adding more store-bought roux or adding a cornstarch (or flour) slurry.

Adding a beurre manie or adding pureed veg were close runner-ups.

Coconut milk and peanut butter didn’t really work. And making your own roux was a lot of effort.

Instant mash and simmering the sauce for longer worked, but with small issues. Instant mash changed the sauce’s texture too much and simmering the sauce for longer resulted in too much volume loss.

Results summary

MethodNotesRating
Store-bought rouxEasy and doesn’t affect taste or texture10/10
Cornstarch/arrowroot slurryVery strong thickening effect and quick9/10
Flour/water slurryStrong thickening effect and quick9/10
Beurre manie (flour/butter)Strong thickening effect and quick7/10
Pureed vegetablesWeaker thickening power, but very easy7/10
Simmering for longerReduced the volume of sauce significantly5/10
Instant mashGave the sauce a heavy texture5/10
Homemade rouxWorked well but a lot of effort4/10
Coconut milkVery weak thickener and altered flavor2/10
Peanut butterVery weak thickener and altered flavor2/10

How to thicken Japanese curry

Less is more with thickening agents, especially powerful ones. 

Start slowly, and add more as needed.

Also, keep in mind that the sauce will continue to thicken as it cools. If you plan to have leftovers, the sauce will thicken at least one level in the fridge overnight. 

If you go too far and the sauce gets too thick, simply add some water or stock to thin it out again.

I go into more detail on the ten different methods I tested below.

Thickening japanese curry with a store-bought roux

Rating: 10/10

Thickening power: strong

Taste/texture: a more concentrated flavor but no texture change

If you’ve used a store-bought roux to make your Japanese curry and you have some leftover, the simplest thing to do is add some more.

This was my favorite method because it was super easy and didn’t adversely affect the taste or texture of the curry.

How to thicken Japanese curry with a store-bought roux:

  1. Heat your curry sauce until it’s simmering.
  2. Add a small amount of the Japanese curry paste to the sauce and stir until it’s dissolved (around a teaspoon per cup of sauce). 
  3. Wait 2-3 minutes to see how the sauce thickens up, and then add more if needed.

As you can see from my picture, I went a bit overboard with the roux and ended up with a very thick sauce. 

Always wait a few minutes before adding extra roux to ensure it’s had time to take full effect. I didn’t and added more even though it wasn’t needed.

It’s perfectly okay (even encouraged) to mix store-bought roux brands, so don’t worry if you only have a spare of a different brand.

Thickening Japanese curry with a cornstarch/arrowroot slurry

Rating: 9/10

Thickening power: very strong

Taste/texture: no change in taste, but a slightly gloopy texture

Cornstarch is a powerful thickener, so be careful not to add too much. 

Go for less than you think you’ll need at first. You can always add more later.

I’ve given this method a high rating because it’s easy and works instantly. It loses a mark for altering the texture of the sauce.

How to thicken Japanese curry with a cornstarch/arrowroot slurry:

  1. Bring your curry sauce to a simmer.
  2. To make a cornstarch slurry, mix together cornstarch and water in a 1:1 ratio. For example: mix 1 tablespoon of cornstarch with 1 tablespoon of cold water. This will be enough to thicken 1-2 cups of sauce. 
  3. Mix the slurry into your simmering sauce and stir well for 1-2 minutes.
  4. Check the thickness.
  5. If it’s not thick enough after 2 minutes, add some more of the cornstarch slurry. 

It’s important to stir the slurry in quickly to avoid clumping.

Don’t leave the sauce simmering for too long after you’ve added the cornstarch slurry, or it will start to thin out again (I try not to go over 5 minutes).

Also, don’t let the sauce boil because this can reverse the thickening effect.

Cornstarch doesn’t taste of much, so it didn’t affect the flavor of my sauce. But it did give the sauce a glossy finish and a marginally gloopier texture.

(don’t worry, ‘gloopy’ sounds a lot worse than it is).

Avoid using cornstarch if you plan on freezing the curry because it can develop a weird texture after freezing.

It also loses some effectiveness if your sauce is very acidic (e.g. if you’ve added lots of tomatoes).

Cornstarch alternatives

Another popular starch-based thickener is arrowroot powder. Arrowroot powder is an excellent gluten-free thickener and freezes well. It works fine in acidic sauces, but you should avoid using it in dairy-based sauces. 

You can sub arrowroot powder in a 1:1 ratio with cornstarch in your Japanese curry.

Other popular options include:

  • Potato starch (sub in a 1:1 ratio)
  • Rice flour (use 2 tablespoons for 1 tablespoon of cornstarch)
  • Tapioca flour (use 2 tablespoons for 1 tablespoon of cornstarch)
  • Flour (use 2 tablespoons for 1 tablespoon of cornstarch, see more detail below)

Thickening Japanese curry with a flour slurry 

Rating: 9/10

Thickening power: strong

Taste/texture: no change in taste or texture

If cornstarch isn’t suitable for you, flour is an easy substitute. 

A flour slurry is very similar to a cornstarch slurry, and they both worked well.

However, there are some minor differences:

  • You’ll need to use more flour than cornstarch to get the same thickening effect.
  • The sauce will become a little cloudier after you add the flour.
  • You need to simmer the sauce for a few minutes extra to cook off the raw flour flavor. 
  • Flour is more likely to clump than cornstarch.

But really, it just depends on what you have in your cupboard. 

How to thicken Japanese curry with a flour/water slurry:

  1. Bring your curry sauce to a simmer.
  2. To make a flour/water slurry, mix together flour and water in a 1:1 ratio. For example: 1 tablespoon of flour with 1 tablespoon of cold water. This will be enough to thicken 1 cup of sauce. 
  3. Take a few spoonfuls of curry sauce and mix this into the flour/water slurry to form a smooth paste.
  4. Slowly mix the paste back into your simmering curry sauce and stir well for 2-3 minutes.
  5. Check the thickness.
  6. If it’s not thick enough after 2 minutes, add some more slurry.
  7. Simmer the sauce for 5 minutes after adding the last of the flour to cook off any raw flour flavor. 

The extra step of making a paste with the slurry and some sauce helps to ensure a smooth finish.

Thickening Japanese curry with a beurre manie

Rating: 7/10

Thickening power: strong

Taste/texture: no change in taste or texture

A beurre manie is a fancy name for a mixture of flour and butter. 

It’s very similar to a roux. The only difference is you don’t cook it before you add it to the sauce, making it more suited to thickening already-cooked sauces.

This method worked well, but was kind of fiddly to prepare and seems overkill when you can just use a flour and water slurry (see above).

How to thicken Japanese curry with a beurre manie:

  1. Bring your curry to a simmer.
  2. Mix together flour and softened butter in a 1:1 volume ratio (e.g one tablespoon of each) until it forms a smooth paste. Avoid microwaving the butter, soften it with your hands if you have to.
  3. Spoon out a small amount of your (hot) curry sauce and mix it into the beurre maine until it’s lump free. 
  4. Slowly add this mixture back into the sauce stirring to incorporate it.
  5. Keep stirring and let the sauce simmer for 2-3 minutes.
  6. The sauce should thicken. If it doesn’t thicken enough, add some more of the beurre manie in. 

You can use any flour in your beurre manie, so pick your favorite.

The step of adding a small amount of your sauce into the paste first helps to ensure your sauce remains lump-free.

If you have leftover beurre manie after thickening your sauce, you can wrap it in plastic wrap and store it in the fridge for up to two weeks (if you think you’ll need it again).

Thickening Japanese curry with pureed vegetables

Rating: 7/10

Thickening power: medium

Taste/texture: slightly diluted flavor with a heavier texture

Traditional Japanese curry is made with potatoes and carrots. 

A quick and easy way to thicken the sauce is to turn the potato and carrots into a thick paste, which you can mix back into the sauce.

Although this isn’t the strongest thickening method, I gave it bonus marks because it doesn’t involve any new ingredients. 

How to thicken Japanese curry with pureed vegetables:

  1. Mash or puree some cooked vegetables (ideally ones you have just removed from the curry sauce, I took the carrots and potaoes from my sauce).
  2. Keep mashing until you have a smooth consistency.
  3. Stir the mashed vegetables back into the curry sauce until it’s well incorporated.

You should notice the sauce has a thicker consistency.

If you don’t want to use the veg in your curry, you can cook some fresh vegetables to puree. Potatoes, carrots, and cauliflower are all good options. 

Pureed veg isn’t the best thickener, so it’s more suited to curries that only need a little help.

The sauce became sightly heavier in texture after I added the veg, and the flavor was somewhat diluted due to the extra starchiness, but nothing drastic.

Bonus point: this is a great way to hide vegetables from picky eaters!

Thickening Japanese curry with instant mash

Rating: 7/10

Thickening power: strong

Taste/texture: slightly diluted flavor with a heavier texture, a bit grainy

Instant mash or potato flakes work by absorbing liquid. As they absorb liquid, the flakes expand, and this gives the sauce a thicker texture.

This method worked well, but it changed the sauce’s texture more noticeably than other methods, so I docked it a few points.

How to thicken Japanese curry with instant mash:

  1. Bring your curry to a simmer.
  2. Sprinkle some potato flakes into your curry (a tablespoon per cup of sauce is a good guideline).
  3. Stir well and watch as the sauce thickens.
  4. Wait 2-3 minutes for the potato flakes to take full effect.
  5. Add more potato flakes if the sauce isn’t thick enough.

Going slowly is essential with potato flakes because they can alter the sauce’s texture, so you don’t want to go overboard.

The potato flakes gave the sauce a heavier feel and made it more filling.

After I’d added quite a bit of instant mash, the sauce started to get an unpleasant grainy feel to it. Although this only happened once I’d added a significant amount.

An alternative to potato flakes is to grate some raw potato into the sauce. The grated potato will cook almost instantly and release starch, which will give the sauce a thicker texture.

Thickening Japanese curry by simmering the sauce for longer

Rating: 5/10

Thickening power: strong

Taste/texture: more concentrated flavor but no texture change

Don’t want to mess around adding things to your sauce?

A tried and tested method of thickening sauce is to let it cook a little longer.

This method worked but left me with a lot less sauce, which is why I scored it so lowly.

How to thicken Japanese curry with pureed vegetables:

  1. Simmer the curry on low and wait for the excess water to evaporate (make sure there’s no lid on your pan). 
  2. Stir the sauce occasionally until it’s thickened up to your desired consistency.

If you’re worried about your vegetables or meat overcooking while you simmer the sauce, take them out and leave them on the side until the sauce is nearly thick enough. Then add them back in 2-3 minutes to heat through.

Despite how easy and accessible this method is, I don’t recommend it unless you have a decent amount of excess sauce or you only need very minimal thickening.

The sauce thickened, but I was left with a lot less sauce. And as a fan of saucy curry, this was a big downside for me.

It also took the longest because the thickening wasn’t instant like most other methods.

Thickening Japanese curry with a homemade roux

Rating: 4/10

Thickening power: strong

Taste/texture: no change in either taste or texture

If you don’t have any pre-made roux left or made the sauce from scratch, you can always make a new roux.

However, I don’t recommend this method because it’s more work than necessary. 

How to thicken Japanese curry with a homemade roux:

  1. Bring your curry sauce to a simmer.
  2. Measure out equal parts flour and butter (e.g one tablespoon of each)
  3. Melt the butter over a low heat in a small pan.
  4. Once the butter is melted, add the flour and stir it in until there are no lumps.
  5. Stir continuously for 5 minutes to cook off the raw flour flavor.
  6. After 5 minutes, spoon out a few tablespoons of your simmering curry sauce and mix it into the roux to make a smooth paste.
  7. Slowly add the paste back into your main sauce, stirring to keep it smooth.
  8. Wait 2-3 minutes for the sauce to thicken and decide if you need more roux.

If you don’t have butter, you can use a different fat such as oil.

A roux makes a great starting point for Japanese curry because they add flavor. 

But as you can see, making one is quite a bit of work. And if all you want to do is thicken an already flavored sauce, there are much easier ways (like a beurre manie or a slurry).

Thickening Japanese curry with coconut milk

Rating: 2/10

Thickening power: weak

Taste/texture: coconuty taste, creamier texture

Coconut milk is often suggested as a thickener for Indian curries, so I wanted to see if it would work with Japanese curry.

Of course, this is only an option if you like coconut and don’t mind altering the taste of your Japanese curry. The final result certainly wasn’t traditional tasting!

It also didn’t thicken my sauce much, so I only recommend it if you need a tiny amount of thickening.

Simply add the coconut milk into your curry and stir.

Thickening Japanese curry with peanut butter

Rating: 2/10

Thickening power: weak

Taste/texture: nutty taste, no texture change

The results of peanut butter were very much the same as coconut milk.

Overall, I don’t recommend using peanut butter for Japanese curry because it alters the taste too much and is only a weak thickener.

Again, all you need to do is add a few spoons of peanut butter into your sauce and stir until it’s incorporated.

Other thickening options I didn’t try

This list I’ve produced here is by no means exhaustive, and there are a few other options I want to mention.

Most of these methods are more common in Indian curries, but there’s no reason they wouldn’t work in Japanese curry.

  • Cooked and pureed lentils will thicken a curry sauce and add bulk.
  • Ground nuts such as cashews are a common thickening agent for curries.
  • Cooked and mashed beans work similarly to lentils, providing bulk and thickening power.
  • Xanthan gum. This is a popular keto thickner and a little goes a VERY long way. Make a slurry with a 1/4 of a teaspoon and 1 tablepsoon of water, this will thicken one cup of sauce.
  • Dairy products like sour cream or yogurt. These will significantly alter the taste of the curry and make it more creamy.

How to thin out a curry that’s too thick

Don’t worry. We’ve all been there.

If you accidentally go too far the other way, you’ll be glad to hear it’s easy to thin out a sauce that’s too thick.

All you need to do is add in some extra water or stock.

If the curry has become too concentrated, go for water to help dilute the flavors.

But if you think the sauce might become too watered down, use stock.

Tips for next time (how to avoid a runny sauce)

Hopefully, you’ve managed to fix your runny sauce with one of the suggestions above, but I also want to give you some tips on how to avoid this happening again.

Pay attention to the water/roux ratio

The curry roux (whether homemade or shop-bought) is what thickens your Japanese curry sauce. 

Add too much water, and the roux won’t be able to thicken the curry effectively.

Most shop-bought options will have instructions on the back of the pack telling you how much water to add per block of roux. 

Follow these! 

If you don’t, you can end up with an overly runny sauce.

If anything, add a little bit less water than it calls for (it’s easy to add more water in, but it’s impossible to take it out once you’ve added the roux).

If you’ve made your own roux, the standard ratio for Japanese curry sauce is:

1 tbsp butter and 1 tbsp flour per 1 cup of water. 

However, if you want a really thick sauce, you can increase this to 2 tbsp of butter and 1 tbsp flour per cup of sauce.

Beware of watery vegetables 

Customizing your curry with different veggies is common, with zucchini, tomatoes, and mushrooms being firm favorites.

But the problem with going off-piste is that you can run into unexpected problems.

Zucchini, tomatoes, and mushrooms all release water as they cook. 

By adding them to your curry, you’re inadvertently adding extra water, which thins out your sauce.

You can still add these veggies, but remember to reduce the amount of actual water you add to keep the sauce nice and thick.

Cook the roux less (for homemade roux)

The longer you cook a roux, the darker it becomes, and the less thickening power it has.

There are four roux stages:

  1. White
  2. Blonde
  3. Brown (similar to peanut butter)
  4. Dark (similar to melted chocolate) 

For Japanese curry, a dark blonde roux is ideal (between stages 3 and 4). It should take around 15 minutes of heating and stirring to reach this stage.

If your roux is darker than this, it might not thicken the sauce effectively.

You don’t need to worry about this with shop-bought roux because they’re pre-cooked for you.

Ditch the lid

Most Japanese curry recipes assume you’re using a pan without a lid, and the quantity of water reflects this.

Lids prevent water from evaporating, so if you use one, the end result will be a runnier curry than you were expecting.

What if I’m using a slow cooker?

If you’re using a slow cooker, the best option to get a thick curry is to use less water than called for in the first place.

Check your roux instructions and see if they have a note about cooking in a covered pot. 

If not, I’d use 25% less water.

Your second option is to leave the lid off the slow cooker for half an hour at the end of cooking to let the water evaporate.

However, be aware that this can put your curry in the ‘danger zone’ for bacteria because the slow cooker will cool down.

How To Thicken Japanese Curry

If your homemade Japanese curry is just too thin – I have the answer.
In this recipe, I share the best method to regain a nice thick consistency in your Japanese curry.
No ratings yet
Prep Time 5 mins
Cook Time 5 mins
Total Time 10 mins
Course Main Course
Cuisine Japanese
Servings 1 person
Calories 70 kcal

Ingredients
 

  • 1 portion Japanese curry
  • 1 portion store-bought roux

Instructions
 

  • Heat your curry sauce until it’s simmering.
  • Add a small amount of the Japanese curry paste to the sauce and stir until it’s dissolved (around a teaspoon per cup of sauce).
  • Wait 2-3 minutes to see how the sauce thickens up, and then add more if needed.

Nutrition

Serving: 100gCalories: 70kcal
Tried this recipe?Let us know how it was!

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