If you add spices to boiling pasta, will it absorb spices/flavours?

Poorly. Pasta doesn't absorb all that much flavor from spices in the water, other than maybe salt (and even then you must add excessive amounts of salt to make the resulting pasta evidently salty.) Add spices to whatever sauce you pour on the pasta, otherwise you're wasting like 90% of them.

An alternative would be kneading the spices into the pasta dough. There are several pasta brands with spices/herbs in the dough like that.

One important fact to note here is that many spices are oils or oil-soluble. Pepper, for example, will dissolve effectively in oil, and thus the flavor of pepper can be imparted into other things thereby; however, if you attempt to dissolve it in water, you'll mostly end up with the pepper just staying in the peppercorn (if whole or large pieces) or floating to the top/sinking to the bottom if ground.

That's one reason why you have sauces: they're ways to get oils onto the food. The sauce has some oil in it, the pepper oil dissolves into that oil, and tada, you have yummy tasting food.

Only certain things will dissolve in water, like sugar and salt. Some things, like coffee, will dissolve partially in water (sometimes that's helpful, if the oil doesn't taste very good). But many spices are oils or oil-soluble, particularly chile/pepper type spices (the "hot-as-in-spicy" ones).

That will work only for water-soluble spices, and you will still end up pouring a lot of spices away with the water.

I once took a cooking class with Bavarian chef Alfons Schuhbeck, and his recommendations were:

• Always oversalt pasta water, as this is the only way of getting flavor into the pasta. (Which implies most of the salt is poured away with the water.)
• Instead of salt water, you can also use broth if the flavor fits your dish.
• Boil the pasta for 4 minutes less than indicated on the packaging. Then strain, pour on a baking sheet or similar, add some oil and mix well so the pasta gets covered with oil. Then finish cooking the pasta in the sauce, so the pasta will absorb the flavor of the sauce.

The last point can be taken one step further by preparing a somewhat watery sauce and cooking the (raw) pasta in the sauce. It will take a bit longer than usual, and you have to develop a feeling for just how much liquid you will need (or keep and eye on the pasta and add more water as needed—a bit like making risotto). However, the pasta will absorb a lot of flavor from the sauce, and no starch from the pasta will end up getting poured out with the water (it all goes into the sauce).

As an additional benefit, you have only one pot to clean in the end instead of two.

In my experience, not really. Most of your spices end up in the water.

Now, something that I have tried that has worked is sauteing the pasta in spiced oil. The downside to this is that your sauce won't stick to the pasta as well. If you really want to give your pasta that extra kick of spice, you would need to either season the pasta dough before you cook it - I've done this with bread and it works wonderfully -, season the oil that you add to the pasta after you've combined it with sauce, or add it to the sauce itself.

A potential positive benefit to adding spice to the water is that you get a starchy flavored water that you could add to your sauce. Not really sure if you'd want to do that though honestly. I've never noticed any problem with getting the sauce to stick to the pasta so long as I didn't add oil to the pasta before mixing it with the sauce.

Bonus fact: Sous vide spaghetti turns into a brick and is a lot harder to separate than sous vide rice.

It depends on the spice, and how exactly you add it.

As a general rule, if the spice dissolves well in water, you can do this with it, though you will only get a subtle flavor this way, and most stuff this works with is not widely used for flavoring pasta. Salt is the primary example. Other possibilities that come to mind include sugar (of almost any kind), vinegar, and matcha (though just getting green-tea flavored pasta is much cheaper than using matcha to flavor your pasta).

Broths can also be used to achieve a similar effect. Bullion (of almost any type) and daashi can both be used for cooking pasta, and impart part of their flavor to the pasta in most cases.

For most stuff though, it doesn't work very well if you just add it to the water. A vast majority of 'spices' have flavors produced by chemicals that are not readily soluble in water. Classic examples that might otherwise be used with pasta include all types of pepper, garlic, saffron, paprika, cumin, and curry. In general, the spice will just not properly diffuse into the water enough to be absorbed by the pasta.

Depending on the desired flavor however, and how much prep-time you have, you might be able to get there, though it will still be a subtle flavor. Depending on the spice, you can:

• Create a decoction or infusion using water, producing enough of the resultant liquid to cook the pasta in. This works well with certain spices that are often used for making herbal teas, such as ginger, cloves, or cardamom. I've done this before with ginger when making udon noodles, and can say it works reasonably well, but it's a pain to prepare (you have to let the decoction steep for multiple hours usually), and it tends to use a lot of the spice, making it impractical for expensive spices like cloves or cardamom.
• Create an infusion using alcohol, producing a reasonable amount of concentrated liquid that you then add to the water while cooking the pasta. This works best with high-proof (150 or higher, higher is better up to about 190 proof) unflavored vodka as the base, but also takes a very long time. If you add it in at the right time while cooking the pasta, the alcohol will boil off but leave the flavor behind. Works best with very oily spices like pepper or cloves. This doesn't use quite as much of the spice as either of the first option.
• If you can find a liquor or liqueur with the flavor you want, you can use that as part of the cooking stock, similar to the above. Pepper-infused vodkas are not hard to find and work great for this. I've seen some other rather unique recipes that do this with more unexpected flavors too (one of my slightly less than normal friends has this amazing pasta dish that uses gin of all things when cooking the pasta).

An alternative approach would be to double-cook the pasta, first boiling or steaming it, and then sauteing or frying it, and adding the spices to the oil used in the second step. Yakisoba and chow mein are the closest standard dishes to this approach, but it's rare to see either of them use the spices when cooking instead of as part of the sauce.

Of course, the best option is to just add the spices to a sauce. Most sauces have enough oil in them that the flavors diffuse well, so it's not an issue of the pasta absorbing them or not. It also gives you a lot more control over the exact amount of flavor in the dish. Keep in mind that a sauce can be as simple as some oil infused with whatever spices you want to use, it doesn't have to be complex to be good.

The answer is yes. Those saying otherwise most likely never tried doing this. However, you need a considerable amount of spices, say 12 peppercorns, 6 cloves, and a cinnamon stick. The effect is enhanced if you let the spices simmer in the water for a some time before adding the pasta. Why don't you just go ahead and try it yourself? Half a package of pasta and the aforementioned spices shouldn't add up to much more than a dollar.

As many answers note, this is not recommended. However, a variant that is used in many recipes is using the same water to boil vegetables and then pasta. In this way, some of the flavour of the vegetables that would go lost with boiling is transferred to the pasta. For instance:

• Pasta con le sarde (fennel)
• Pasta with pesto, potatoes, and green beans (potatoes and green beans)
• Pizzoccheri alla Valtellinese (cabbage/spinach/chard and potatoes)

The best way is to finish cooking the pasta in the pasta sauce. Then the sauce and the pasta will blend together and you will taste of sauce in every bite of the pasta.

Generally it's almost always wasted to add spices to the water while boiling as 99% of the spices will go down the drain. You need tu use a lot of spices to get any effect. It's better to just add the spices after you have boiled, or in the case of pasta, to the sauce. Another great way when you for example boil potatoes is to boil sous vide with a little water and spices in the bag. Then the potatoes will absorb almost all of the spices. Boiling potatoes sous vide is awesome by the way, even without spices.