infusion time of Gaggia Classic too long

[SPN]

It’s generally said that extraction time should be 20-30 seconds. When they say “extraction time,” it sometimes includes infusion time (steeping time), i.e., the time from pushing the button until it starts extracting (dripping); and sometimes they count from when it actually starts extracting (i.e., extraction time does not include infusion time).
Either way, I’m wondering how long the infusion time is supposed to be. I have Gaggia Classic Pro and I think my infusion time is too long. It takes about 15 seconds from pushing the button until it starts extracting (dripping). Then once it starts extracting, it takes 20-30 seconds to get a right amount of shot, which seems fine.
The problem is that my espresso tastes bitter. I tried different combinations of grind size, coffee grams etc. and they are all bitter. I’m using good beans freshly roasted in the local roaster who knows Gaggia well. I’d like to control infusion time and see if it solves the bitterness problem. How can I control the infusion time and what does too long infusion time mean?
I'll appreciate your comments!

 

[shadow745]

Honestly it's best to ignore what time/volume/yield 'should be' as every setup, coffee, environment, expectation will vary. The bitterness you are experiencing could be a number of things, not just time alone. Yes if the water is in contact with the coffee a bit long it can overextract, leaving you with less than great flavor. Water temperature, brew pressure, etc. can affect that as well. I have my setup dialed in to give quite long extractions time-wise, but low volume. I have pump pressure a bit lower, grind quite fine, updose and lightly tamp so I don't see the first drip until upwards of 20 seconds and the total extraction averages at least 50 seconds and gives me a yield around 1 oz. or so. I never go by time/volume/weight of extraction, but have checked those things a handful of times out of curiosity. I like very bold/heavy textured ristretto style extractions, but it's not for everybody and doesn't take much variance to throw things off quickly.

You mentioned 'good beans freshly roasted'... how long post roast have they mellowed out before using them? Of course fresh is best, but with espresso using coffee that's too fresh can make quite a negative impact. For what I like/roast I let each batch mellow out 7-8 days post roast before using, otherwise it's not very smooth/balanced.

 

[SPN]

Thanks Shadow 745! Your comment is very helpful. I cared about the numbers and conditions, but to be honest I agree with your opinion. My condition is out of what is generally recommended, but similar condition as yours makes better results. I'll trust my taste (I like ristretto, too) and won't care about the number and conditions. Thank you!!