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Why is boiling water needed to cook pasta?


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#1 sygyzy

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Posted 03 October 2009 - 12:22 AM

We know from Harold McGee that we don't need nearly as much water as previously though. We also know to salt heavily because to flavor the pasta, not to speed up the boiling.

But why do we need boiling water at all? I have seen someone put dry pasta in a pot with cold water and turn on the heat. They wait until the pasta is soft and take it out.

I laughed quietly and wanted to point out how that was all wrong but I didn't have an explanation as to why.

#2 Blether

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Posted 03 October 2009 - 05:03 AM

Let's recap on a basic piece of kitchen physics.

Liquids rise in temperature as they absorb heat. In the same pan over the same heat, different liquids will warm up (their temp will rise) at different rates. Once a liquid starts to boil, its temperature remains constant as it absorbs more and more heat. This heat goes to changing the liquid into gas, boiling it off.

Different pots and pans will absorb different amounts of water in order to heat up.

So, not 'wrong', but a question of communication. How can we write a repeatable recipe ? Boiling water at 100C is a known quantity - if you adjust the heat so it stays on the boil, that's a bath of water at 100C, regardless of the temperature of the room, the min & max heat-producing capacity of the stove, the size & shape of the pot, or crucially the actual rate of heat input over quite a wide range. So I can give a recipe that has a timing for any given pasta - or put another way, pasta makers can quote a cook time. What's a little unclear to me is whether the timing is meant to start once the pasta is entirely submerged or once the water boils again (or something else). IME (and cooking on powerful gas) there's not a big time difference between the two, and timing factory pasta from immersion gives good results: we are encouraged to judge our pasta by testing to the bite, and that's entirely correct and one of the reasons why the method you saw isn't 'wrong'. My practice is to set a timer based on the factory-stated cook time (adjusting for any final cooking together with a sauce) anyway. If I have hands enough and time to test diligently, that's one thing; if the timer catches me I have a backstop: anyway you need the bite-testing when you make your own pasta, but De Cecco's products - and those of others - are consistent and I'm quite relaxed about it.

Secondly, in a field with so many a la minute sauce preparations, it's often vital to be able to predict when each piece will be ready in order to get best results - so again, predictability is important.

Lastly, I like to follow the advice to use a rolling boil, because after a first stirring as the pasta first softens and the water boils again, it means I don't have to stir any more.

The kitchen is full of - brimming with - myths of every colour. I've been indebted for some time to Aidells & Kelly for their advice on pre-salting meat. Isn't one of the beauties of food work, that we can 'suck it and see' ? There's always an ultimate proof - for each individual cook :biggrin:

Edited by Blether, 03 October 2009 - 05:08 AM.

QUIET!  People are trying to pontificate.

#3 David A. Goldfarb

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Posted 03 October 2009 - 05:20 AM

I think McGee's article showed that it was possible to soften dry pasta and cook it to an acceptable temperature with less water than traditionally recommended, and that smaller amount of water would contain more starch and could be added back to sauces, but McGee did not demonstrate that the pasta would have the most desirable texture by cooking in a small amount of water, at least not if you like your pasta al dente.

Unlike some other things, I think you want pasta to cook unevenly, so it softens on the outside and retains a thin firm core and has a gradation from soft to hard. The way to do that is to cook it quickly in a large amount of boiling water, removing it from the water before the center gets too soft. Cook it in too little water as McGee tested in his article, or too cold water, and it will cook to the same boring mushy texture all the way through.

#4 RobertCollins

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Posted 03 October 2009 - 07:27 AM

I really think the two answers above are really good but they lead me to a follow up.

Does it matter whether you fill the pan to start with hot water or cold. This query is because a friend saw me filling a pot on my stove top and noticed that I had both hot and cold faucets there. His proclamation was he would never consider filling a cooking pot with hot water as it had off-gassed the oxygen and would spoil the flavor of the food.

My hot water comes to my stove top faucet straight from the hot water tank and is recirculated so it bypasses the hot water mixing devices. I run my tanks at 150°, this saves about 20 minutes for a gallon and a half or two to come to boil.

I think I read long ago some where that the reason for a lot of water was to return the pasta water to the boil as quick as possible to avoid the soggy texture.



#5 gfweb

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Posted 03 October 2009 - 07:38 AM

Off-gassed the oxygen??

Boiling will do that better and more completely than any hot water heater. And how does he know that O2 contributes to the flavor of pasta? It doesn't get oxidized as in a maillard rxn in a pan.

#6 Darienne

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Posted 03 October 2009 - 07:47 AM

So then why were we taught to start with cold water and heat it to the boiling, not just for pasta, but everything pretty much?

We do it in our house because our country well water is very hard and is run through a water conditioning process which uses salt. Only our kitchen cold water tap bypasses this treatment and has water straight from the well...which explains our constantly plugging coffee machine.

learn, learn, learn...

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#7 David A. Goldfarb

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Posted 03 October 2009 - 08:44 AM

Hot water, by the time it comes from the boiler through the pipes to the tap is likely to bring more things with it than cold water, as I've always understood it, and that's why it's usually recommended to start with cold water for anything in the kitchen, unless you have a hot water heater at the tap.

#8 qrn

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Posted 03 October 2009 - 09:04 AM

If you have ever drained your hot water tank,you are aware of all the "stuff" that comes out, you could be cooking your pasta in that "stuff"


#9 OliverB

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Posted 03 October 2009 - 10:27 AM

I used to use hot water from the tap until I read in one of Andrew Weil's books that hot water might contain all kinds of things picked up in the heater or the pipes, which made some sense to me. Our house was built in 1950 or so, who knows what pipes they used. He also suggests to let the cold (standing in the pipes) water run out first, which I don't always do, but since I read that I only use cold water. Aside from the fact that it takes a good while for the hot water to get hot in the kitchen, the plumbing seems to do a round about under the house (the water heater is only maybe 20ft away from the kitchen sink) or something.

As for the original question here, I never measure the water I use, I use my "large" pot and fill it up to maybe 2/3, bring that to a boil, pour in salt, and throw in the pasta. I always find that the instructions on the packages overstate the cooking time so I cook pasta several minutes short at times. I don't really see a point in playing with the amounts though, or to get all scientific about it? I did not see McGee's article, but this almost seems a bit like he's running out of ideas? Pasta would probably get soft just fine if you just soak it in cold water for an hour or so, but does it matter? Sometimes he seems to overcomplicate things a bit, as much as I love his work :-)
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#10 Katie Meadow

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Posted 03 October 2009 - 11:10 AM

I've eaten pasta cooked a variety of ways by many different people over the years; cold water to start, minimum total water, cooking at a simmer. The best taste and texture seems to result from starting pasta in a generous amount of water that's at a rolling boil, with salt added when it starts to boil. That way the water has the best chance of keeping at a continuous boil and the most consistently al dente pasta results. If you aren't convinced, try cooking pasta in cold water or very little water, and see what you think of it. It's a relatively cheap experiment.

I was taught never to drink or use hot water from the tap except for washing dishes; my mom believed that the hot water tap carries more impurities than cold. I don't know if that's really true, but like so many other things I do I don't have science to back me up. So, it takes a few extra minutes to bring cold water to a boil. Yes, that can definitely be annoying with a gas range that is underpowered, and I can see the temptation to start with the hottest water possible. But I don't. And I don't pay much attention to the recommended cooking time on the box. I just taste it frequently during the final minutes. One thing I've noticed is that spaghetti often continues to cook while draining (and I learned to NEVER rinse pasta with cold water if you are eating it hot), so I take it out about 30 seconds before I think it's perfect.

#11 sygyzy

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Posted 12 October 2009 - 02:45 PM


Sorry for not checking in sooner. There is a wealth of information presented in the replies but sadly I don't think any answers my question. I was not asking about the amount of water or whether to start with hot or cold water. I was asking why we drop in pasta to boiling water instead of starting it off in a pot of cold water set over a flame. Even for those who start with cold water, you don't add the pasta until it's boiling. Nobody ever starts pasta in cold water then heats it up ... except my roommate. That's why I am asking.

#12 Tri2Cook

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Posted 12 October 2009 - 02:57 PM

I think Blether did answer that question quite nicely. If the recipe/package tells you to drop it in boiling water then it can tell you to pull it from the water in x amount of time and be sure of the desired results +/- a very small margin of variance because it knows the precise temp of the cooking liquid. If they tell you to toss it in cold water they have no way of knowing the actual temp of your cold water, the power of you heating device, the ambient room temp, etc. so they have no way of knowing how long it will take the water to heat. Without that knowledge, the best approximation of cooking time they can give you is "cook until done" which is a valid statement but not sufficient for many consumers who want to be told to set the timer for x number of minutes and go watch tv without worry.
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#13 plattetude

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Posted 12 October 2009 - 03:40 PM

Not to mention what David explains:

Unlike some other things, I think you want pasta to cook unevenly, so it softens on the outside and retains a thin firm core and has a gradation from soft to hard. The way to do that is to cook it quickly in a large amount of boiling water, removing it from the water before the center gets too soft. Cook it in too little water as McGee tested in his article, or too cold water, and it will cook to the same boring mushy texture all the way through.

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