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tdatta

Sous vide caramelized onions for soup

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So I thought I would try out caramelizing onions in a water bath. I had seen a number of references to this online in a number of places like http://emilysculinaryadventures.blogspot.com/2013/01/another-sous-vide-trick-uber.html or  http://www.orgasmicchef.com/soup/sous-vide-caramelised-onions/ as it seemed like a great way to save some effort and explore another SV technique. 

 

One of the things that I have read is that onions can release gas and cause the SV bag to balloon and possibly explode. I don't know the mechanism behind this, but I have read that one possible way to avoid this is to pre-sauté the onions a bit. Again, not really sure why. But I did so to be safe, I sautéed the onions with no added fat, I used yellow onions and waited till they got a little bit of color but were mostly dry (for vacuum sealing purposes). Then I sealed the onions with about a teaspoon of chicken stock concentrate, here is the before picture:

 

before.jpg

 

I put it in the bath at 86 C, just to see if any bubbles would form, it was stable after 4 hours, so then I increased the temperature to 96 C and monitored it for another couple of hours, again no bubbles. So i left it at 96 C overnight for a total time of about 10 hours at that temperature. When I went to bed I had not seen much difference. In the morning I notice a lot of brown liquid in the bag but the onions themselves appeared to not have gotten much darker.

 

I tried an experiment where I increase the bath temperature to 98 C for a short while, within minutes I noticed bubbles of gas forming inside the SV bags. The bubbles appeared to be produced similar to the bubbles produced during the phase change of boiling water at the bottom of a pot, but again I don't know for sure. The bubbles caused the bags to start floating, and then I reduced the temp back down to 96 C at which temperature the bubbles stopped forming, I let it stay there for about another hour. During this time the bubbles gas slowly disappeared.

 

The end product looked like this:

after.jpg

 

As you can see there was a great deal of total color change. The onions themselves were mostly translucent, I assume that this is because when caramelization is done in a pan the brown bits stick to the onions and in this case they remained in the liquid. Interestingly, the bubbles were completely gone when the bag was brought down in temp. A possible hypothesis is that there is something in the onions that is reducing the boiling point of water, or that has a lower boiling point than water and thus is boiling within the bag. However, upon cooling it changes phase back into liquid? 

 

The end product was incredible for making French onion soup. My possibly unorthodox method was to get a roux (with some thyme and bay leaves) to the desired color, then add the stock (beef and pork) and SV onions (including liquid). And then simmer for about 30 minutes. I must say that this soup had an incredible depth of flavor that I have not achieved in soups made with traditionally caramelized onions (that were simmered for much longer).

 

I am definitely going to do this again, possible freezing the bagged onions so that I can make french onion soup supper quickly in the future.

 

To summarize:

1. Onions sauteed with no fat till just a little bit of color on the edges.

2. Vacuum sealed with a little bit of concentrated stock.

3. Sous vide for about 10-12 hours at 96 C. (Keep an eye on it to see if bubbles form, reduce temp if needed).

4. Use as needed for soups or whatever.


Edited by tdatta (log)
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They look and sound great!  Is there a reason you sautéed them with no fat? 

 

I wonder whether the addition of a small amount of baking soda might contribute to the maillard reactions taking place, and add even more depth of flavour?


Edited by Matt L (log)

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Yes I think baking soda might help. I just need to learn how to use it properly. Last time I overdid it while caramelizing onions in a pan and found that it totally broke down the pectin and left me with mush.

I used no fat because I didn't want to add any additional liquid. I reasoned that I could get any water from the onions to evaporate but that fat would stick around and make it difficult for me to get a good vacuum. The sealer that I have is pretty limited in its functionality.

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Though I haven't tried to caramelize onions themselves in a circulator, I have used one to create a caramelized onion water (and subsequent fluid gel) that I used for a final dish. I cut a bag of white onions very thin using a mandoline and then sealed it under high pressure with nothing else. Then I cooked the onions at 85C for 96 hours. The onions started out white, were yellow on day 2, brownish on day 3, and deep brown by the end. Here's the bag after 96 hours. All the liquid in there is from the onions themselves.

 

onion_water-1.jpg

 

I strained the liquid at this point. The onions were pretty much spent. I thought about trying to dehydrate them, but they had given up all of their flavor to the liquid. I moved the water to a pot on the stove, brought it to a boil, and added 1% of its weight in salt and agar agar.

 

onion_water-2.jpg

 

I transferred the liquid to a container and let it set up in the fridge. After a few minutes, I had this:

 

onion_water-gel.jpg

 

Then I blended it up and transferred it to a squeeze bottle. The resulting fluid gel had the texture of ketchup but tasted like really intense French onion soup. It's great on a grilled cheese. Here's the dish I made it for --- hangar steak (SV -> grill sear) with SV braised daikon and baby bock choy, SV enoki mushrooms, onion fluid gel, and sesame seeds.

 

onion_water_dish.jpg

 

It's a fun condiment. I'd use gellan next time rather than agar, but otherwise I'd make no changes... though I might try adding some sliced garlic next time. If I was just trying to caramelize onions for soup, I'd still use the stovetop. It's faster and I think the texture would probably be better.

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Unless I misunderstand what you are saying, I believe we have done the same thing, apart from forming a gel. I think that caramelizing onions in a pan is actually caramelizing onions, whereas doing it in a bag produces the caramelized water as you referred to it. The difference being whether the surface of the onion takes up the brown bits or whether the liquid retains the color (and flavor). I think that the primary advantage this method yields is that the onions flavor comes out into the liquid, which results in what can be perceived as a soup that has simmered for longer (uniform flavor instead of distinctly flavored components).

From a texture perspective, I found the spent onions to actually be ideal for the soup. Maybe crunchier onions produce better soup, but this worked quite well.

I really like your idea of converting it into what is essentially an onion concentrate condiment, I think I will give it a shot.

Could you please explain the reasoning behind blending it after it set? Was the result a thickened liquid, and if so could that be achieved with something else. I'm not familiar with gellan, so could that be what you meant? What I remember about agar is that the gels are quite "brittle".

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Though I haven't tried to caramelize onions themselves in a circulator, I have used one to create a caramelized onion water (and subsequent fluid gel) that I used for a final dish. I cut a bag of white onions very thin using a mandoline and then sealed it under high pressure with nothing else. Then I cooked the onions at 85C for 96 hours. The onions started out white, were yellow on day 2, brownish on day 3, and deep brown by the end. Here's the bag after 96 hours. All the liquid in there is from the onions themselves.

 

attachicon.gifonion_water-1.jpg

 

I strained the liquid at this point. The onions were pretty much spent. I thought about trying to dehydrate them, but they had given up all of their flavor to the liquid. I moved the water to a pot on the stove, brought it to a boil, and added 1% of its weight in salt and agar agar.

 

attachicon.gifonion_water-2.jpg

 

I transferred the liquid to a container and let it set up in the fridge. After a few minutes, I had this:

 

attachicon.gifonion_water-gel.jpg

 

Then I blended it up and transferred it to a squeeze bottle. The resulting fluid gel had the texture of ketchup but tasted like really intense French onion soup. It's great on a grilled cheese. Here's the dish I made it for --- hangar steak (SV -> grill sear) with SV braised daikon and baby bock choy, SV enoki mushrooms, onion fluid gel, and sesame seeds.

 

attachicon.gifonion_water_dish.jpg

 

It's a fun condiment. I'd use gellan next time rather than agar, but otherwise I'd make no changes... though I might try adding some sliced garlic next time. If I was just trying to caramelize onions for soup, I'd still use the stovetop. It's faster and I think the texture would probably be better.

 Love this!

 

Why not use xanthan to thicken it and cut out the chilling and re-blending?

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The purpose of blending was to turn the gel into a fluid gel, something that behaves like a gel when it's sitting still but will still pour like a fluid when subjected to shear forces. It's not just a thickened liquid, but one thickened in a particular way that gives it different properties. Ketchup is a common example of a fluid gel... it sits in the bottle as though it were a set gel until you smack or shake the bottle and it begins to pour. ChefSteps.com has a great class on fluid gels but it's behind a paywall. But they have a bunch of videos on YouTube that you can view for free (as well as recipes on their website). Here's a video on how to make an orange fluid gel using low acyl gellan (Kelcogel F) and xanthan.

 

 

And here's a beetroot fluid gel recipe:

 

 

They've got other fluid gel recipes if you search on YouTube or their website. Pretty fun to play around with. Gellan has a better mouth feel and flavor release than agar, and it has a more neutral inherent flavor.

 

I didn't use xanthan by itself because I find that to thicken the liquid to the thickness I prefer, it turns things snotty and has an unpleasant texture.


Edited by btbyrd (log)
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Ah so you wanted a fluid that would exhibit shear-thinning. Cool idea, I'll try it out.

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Brilliant guys!  I bought extra onions to give this a try.  Thanks for the work at posting everything.   Gotta love Egullet.  Great bunch.

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Interesting post!  In Modern Cuisine they have a recipe for caramelized onions using a pressure cooker with canning jars and little baking soda.  I tried it once and thought the traditional way of caramelizing onions produced a more complex and richer flavor.

 

I'll have to try the sous vide version to see if it's better then the pressure cooked version or traditional version.

 

Anyone else try the pressure cooker version?


Edited by torolover (log)

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I tried the PC version. It was OK. Traditional was better.

 

Adding base sped up the reaction, but even a tiny bit broke down the pectin into an onion slime. Not attractive or tasty.

 

I'm pretty satisfied with the stove top or oven methods.

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What's the point of having two circulators if you're not going to use them?

 

I had a big bag of brown onions from Costco and decided to cook sliced onions and onion juice at 85 & 96C respectively. For the sliced onions, I sliced them with a knife and vac packed them raw. Contrary to internet opinion, they don't "blow up", when done this way. there's a small amount of air space inside of the cell walls which comes out as they cook, leaving a small amount of air in the bag. It's not enough to cause them to float substantially. The advantage of packing them raw is that they're dry so you can seal them in a clamp style vacuum machine. If you have a chamber style machine, I'd microwave them until soft, then seal.

 

The onion juice, I made by pureeing in a food processor then passing through a sieve and pouring into ziplock bags. The bags remained completely free from gas throughout the entire cook.

 

Onion Juice at 85C for 16 hours:

IMG_0898.JPG

 

 

 

Onion Juice at 96C for 8+ hours:

IMG_0897.JPG

 

 

 

Sliced Onions at 85C for 16 hours:

IMG_0899.JPG

 

 

 

Sliced Onions at 96C for 8+ hours

IMG_0901.JPG

 

Unfortunately, the 96C cook evaporated off too much water during the overnight cook and the circulator shut itself off so I don't know how long they cooked for.

 

It's interesting how the onion juice browns so much faster than the sliced onions and that the onion juice developed protein clumping like you would see with meat. The 96C onion juice smelled clearly overcooked and burnt, the 85C onion juice smelled wonderful. Unfortunately, when I went to taste them, they tasted one dimensionally sweet, insipid and watery. Not useful for anything. So much for that experiment.

 

The sliced onions are continuing to cook and I'll check back with them after another 12 hours.

 

I also tried baking soda onions and normal onions in the PC a la modernist cuisine and they were a failure. I let them cook for an hour and the baking soda onions were overcooked and burnt while the non baking soda ones were basically white. Given that I have no visibility inside of a PC as it cooks and that reports are the flavor is underdeveloped, I'm going to steer clear of PC for now.

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tdatta:  I used your method with six bags of onions and they turned out marvellous.  The bags did not leak but a strong smell of onions came out of the water bath.  You really have to watch the water level as it evaporated quickly at that temperature.  The onion soup was deliciously favoured with caramelized onions.  I used a little chicken stock and Parmesan brodo for the broth.  Five more bags in the freezer :biggrin:

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tdatta:  I used your method with six bags of onions and they turned out marvellous.  The bags did not leak but a strong smell of onions came out of the water bath.  You really have to watch the water level as it evaporated quickly at that temperature.  The onion soup was deliciously favoured with caramelized onions.  I used a little chicken stock and Parmesan brodo for the broth.  Five more bags in the freezer :biggrin:

 

Thats really great to hear. I was starting to think that maybe I had a one-off experience because of the other posts mentioning lack of flavor and burnt taste. Did you do it at 96 C? Also, did you put stock concentrate in the bag with the onions, or was it just the onions? Im am trying to figure out why others had unsatifactory results.

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What are the advantages of SV over a pressure cooker for this kind of intense maillard effect?

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Thats really great to hear. I was starting to think that maybe I had a one-off experience because of the other posts mentioning lack of flavor and burnt taste. Did you do it at 96 C? Also, did you put stock concentrate in the bag with the onions, or was it just the onions? Im am trying to figure out why others had unsatifactory results.

 

I did them at 96C and I used Modernist Cuisine @ Home beef stock.  There were around 2 large onions/bag and I used 1 tablespoon of stock/bag.  I did brown them a bit in a teaspoon of butter before putting in the bag.  Should have taken a picture of the browning.   Maybe that's part of the difference or even the onions themselves.  I have a Polyscience SV rig and temperature is stable...wonder if temperature variation while cooking played a part.  I had no gas forming at all.  Here is a picture of the finished product.

DSC00679.JPG

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