I lose the flavor of basil when I make pesto sauce Okay, I am writing this question as a result of a long experience in trying to make pesto at home :p I like pesto sauce alot and that is why I have decided that I should make this at home. But for some reason when I make the pesto sauce I almost completely lose the flavor of the basil. It tastes more like oil. And yes I have tried varying amounts of oil and basil and still it tastes atmost like oil with grass in it. Here are more details:

1- I stay in UK at the moment so my basils are nearby and they seems to be grown in Wessex if what is written on them is true. When eaten as a leaf they have quite alot of flavor.

2- I have tried using a blender, mortar and pestle and also manual chopping to create the basil paste. After the chopping is complete, I tried tasting the basil paste before mixing it with oil and other ingredients and it tastes like grass more or less, with very little flavor left. I wash the basil leaves before making the pesto as the package itself says so. I use the mediterennian type basil.

3- It tastes slightly better when it is cooked a little bit or left in oil for some weeks but I have seen instances where freshly made uncooked pesto also tastes great, so I must be doing something wrong.

4- I have never grown the basil myself however to increase freshness I have tried buying already grown basil plants in pots. 

Since I have exhausted all possible methods of pesto making it seems to me that either:

a- Since its quite rainy and not so sunny in UK the basil leaves from here have too much water content and to little plant oil content and they need to be dried for some time before being chopped. This might be supported by the observation that when I chop them on wooden board I get quite a lot of wetness marks on the board. And when I use fresh basil from the pot they are usually well watered.

b- UK basil is not good for pesto? 

c- I am somehow mistreating the basil, I should put much less pressure when using a blade or mortar.

Any suggestions is most welcome :)
I don't have a definite answer, but here are a few thoughts on things that might help.

First, are you drying the basil after washing it?  Shake out the extra water, and pat it dry, maybe let it sit for a bit to evaporate.  The extra water will dilute the pesto a bit, and not be good for the flavor - and if you think the problem might be too much water in the basil, no need to make it worse with extra water on the surface.

Also, are you adding basil stems?  Depending on your variety of plant and the steps you take in your recipe, the soft stems or tips might have more flavor that you're loosing by leaving out, or more plant matter to dilute your basil paste if you leave them in.  Taste the stems, and check your process, and consider if it would help to take the stems out/leave them in once and see if that helps.

Also, it might help to check your salt content.  Some pesto recipes use salt, others use salty cheese, I don't know what your recipe calls for - but salt brings flavors out, and one symptom of under-salting is "watery" flavor, so you might just need a bit more.  Adding salt might help your basil paste taste like "basil" instead of "grass".

I was wondering, given your comment on seeing a lot of water on the cutting board from the basil, if you might be losing flavor from the basil juice when cutting.  Preparing the basil on the cutting board seems the method most likely to have this problem, but even if using the mortar, if you crush ingredients separately then mix in a different container, you might be losing some of the flavor in juices.  On the other hand, most blender recipes (and some mortar and pestle ones) make the pesto in one container, which means the flavor should still be in the mix and not lost- so that might not be the problem, or at least not the only problem.

If the basil is just too mild for your tastes, or has a higher water/flavor oil concentration than you'd like, you might be able to address this by letting the basil dry a little, maybe till wilting, before making pesto to concentrate the flavor a bit.  You might also consider adding some dried basil to strengthen the flavor - I would think completely dried basil would not give the right consistency, but a mix of fresh paste and dried flakes might give the flavor profile you're looking for.

If the basil tastes like the basil you expect when you take a leaf and taste, and grass after it's made into paste, then the flavor must lost somewhere along the way - then you can look at your process and guess where the flavor is going (like sap left on the cutting board, or whatever).  If you taste the leaf and find it doesn't taste basil-y enough to begin with, then it might just be you prefer a stronger basil or a different variety, and doctoring your basil paste with flakes (or even other herbs/spices) might be the only way to get the pesto you want if no other basil varieties are available to you locally.