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Every cook praises how starchy pasta water is great for thickening sauces and helping the sauce cling to the noodles.

But no matter how much pasta water I add, it never thickens the sauce.Yesterday I cooked one pound of pasta in a liter of water (which should yield extra thick pasta water) and the pasta water was still not nearly as thickening as a cornstarch slurry.

Is it over hyped, or is something wrong with me?

  • I use Barilla and DeCeCo pastas
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You seem to have the wrong expectations. No, it will never be as thickening as a cornstarch slurry. If that's the level of thickening you expect, you are really better off using the slurry.

Don't forget that pasta water thickening is a traditional technique from the time when people did not go to the supermarket to buy a pack of cornstarch. They cooked down ripe tomatoes for several hours, and the starchy water saved from needing a few more hours of evaporation. Also, they cooked with homemade pasta, which had some flour residue sticking to it, not the perfectly-gelatinized industrial pastas we buy today.

If this is not how you cook, and if you prefer pudding-thick sauces, then the slurry is probably the better method for you.

I notice Kenji from Serious Eats has also tested pasta water and recommends it for flavor reasons. He also tested it for thickening - but against salted water, not against a slurry. That's what people mean by "it thickens" - it thickens when compared to random liquids, not when compared to thickeners.

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    My takeway from Kenji in The Food Lab was to cook the pasta in much less water than you usually use, then when the sauce is added it will bind / thicken onto the starchy pasta. Seems to work well for me. – Phil Jan 5 '17 at 18:19
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Think of your pasta water as a tool for emulsification, rather than "thickening." Adding pasta water to your condiment pan has the benefit of helping the condiment form an emulsified sauce that adheres to your pasta. Add it a little at a time and swirl the pan vigorously. It also allows you to control how "wet" you want your final result to be without having to create other liquid components. Also consider that praises of starchy water generally come from restaurant cooks who are cooking many servings of pasta in the same water. Dry or fresh, as the evening wears on, that water gets pretty starchy, thus dramatically increasing its viscosity. We just don't cook that way at home.

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    Emulsification, by definition, involves oil. That's not what's happening when you add starchy pasta water to a sauce. – Dan C Jan 5 '17 at 14:54
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    @DanC actually an emulsion only requires two immiscible liquids, not necessarily oil. We are probably still not talking pure emulsification here, but more colloidal dispersion (although pasta sauce can contain oil, and that can get emulsified) but cooks tend to overlook these fine distinctions and just use the "emulsification" term for any process which makes a sauce smooth. – rumtscho♦ Jan 5 '17 at 17:19
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    @rumtscho - given that one of your liquids is clearly going to be water and that the definition of "oil" includes just about anything you'll encounter in a kitchen that's immiscible with water, the distinction you draw is pretty irrelevant. :) – Periata Breatta Jan 5 '17 at 19:47
  • @PeriataBreatta I know - that comment was my way of saying "if we are going to nitpick, here are the exact details" but I think that nitpicking at both mine and DanC's level is irrelevant – rumtscho♦ Jan 5 '17 at 22:09
  • @rumtscho - out of interest, I'm currently trying to figure out what (room temperature) liquid there actually is that isn't either water-miscible or an oil, and the only thing I've come up with so far is mercury. – Periata Breatta Jan 6 '17 at 11:03
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As moscafj said, pasta water cannot be understood as a thickening agent at all. In fact, I understand it as a thinning agent: after your sauce has boiled down to more of a paste (great taste, but not very immersive to the pasta), you'll need some way to make it proper liquid again. What you do not want at that point is to make it runny, watery, hence adding pure water is problematic. Likewise with wine / juices / vinegar etc.: these can make a lot of sense for deglazing at the beginning of the cooking, but adding them at the end will make the sauce watery and also add too much of a raw, unsavoury note. And such pure hydrophilic liquids often don't completely merge with a hearty sauce with considerable fat content, making for an unappetizing phase separation: the water will tend to “wash off” the flavourful parts from the pasta on the plate.

Hence the pasta water: it liquefies the sauce, but at the same time improves contingency due to the starch content. Stock or cream can perform a similar role, but are less neutral. Depends on the kind of sauce what you want. Since you always have the pasta water, that is the first candidate.

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    I agree, in fact, what I usually do, I dump the noodles (2 or 3 minutes undercooked) directly into the thinned sauce and let them sit there for up to 5 minutes. You'll still get them "al dente", if you turn off the heat as soon as you add them. Of course, you need good quality pasta for this. – Oskar Limka Jan 6 '17 at 0:56
  • @OskarLimka : I totally agree about finishing the pasta in the sauce if it seems abnormally runny. Unfortunately if you gave it as an answer, people would likely downvote you for 'not answering the question' even though you solved the actual problem that led up to the question being asked. – Joe Jan 6 '17 at 3:38
  • @Joe indeed, this was not an answer, just a comment. – Oskar Limka Jan 12 '17 at 15:26
  • @OskarLimka : I know ... I just wish it could've been an answer so more people were likely to see it, as it solves the actual problem. – Joe Jan 12 '17 at 19:42
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All answers given here look right, and the folks that answered your question demonstrated they know what they are talking about. But there is a trick that was not mentioned: in case you have a proper pan and are cooking a short pasta (e.g., fusili or penne), you can use the sauce to cook the pasta. It is a different approach, but it is delicious - and the sauce will become thicker naturally. Give it a try!

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  • True, except you probably missed my comment above, which said essentially the same thing (but I still give the noodles a simmer on their own before dumping into the the sauce...) Starting from dry noodles you probably need a soup rather than a runny sauce, a bit like the "pasta e fagioli" which entered the hall of fame in the "soliti ignoti" movie. – Oskar Limka Jan 12 '17 at 15:31
  • @OskarLimka: Ops! Indeed, you have specifically mentioned that!... An additional comment: I've made some pasta directly in the sauce (without pre-cooking them beforehand) and it worked well. The result is surprising, without the "soup effect" you referred to. Anyway, I'll try the pre-cooking stage in my next experiences. Thank you for the tip!! – Humberto Fioravante Ferro Jan 12 '17 at 19:12

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