Greetings fellow brewers,
I brewed up my first batch of beer in about 10 years this last weekend. I bought Jamil's Evil Twin extract kit from Northern Brewer. My original gravity was 1.071, a bit higher than the 1.064 that the recipe calls out. I pitched a smack pack of Wyeast 1056 on 3/25. I have the carboy in a frige with a Johnson controller set to 68*. I had good active fermentation going on 3/26 and then yesterday there was no bubbling going on. I took a sample and it measured 1.023. I am pretty sure that it needs to attenuate more. The smack pack says it is good for 5 gallons up to 1.060 (should have read that part before pitching). Did I underpitch? So I don't know what to do here. Should I pitch another smack pack? should I leave it alone? wait and take more readings? or what?
Any help is GREATLY appreciated.

You probably did underpitch, but probably not a big deal at this point. You could bump up the temp a couple of degrees and rouse the yeast (by rocking/swirling it) and let it go another week, see where you get to.

You also only pitched 4 days ago, so give it another weekish regardless.

I agree...you probably underpitched. But, If I were to guess it is more an issue with lack of Oxygen or other nutrients. How did you aeriate your wort? Shake it? add O2 or filtered air?

Try buying some Servomyces from White labs or the Wyeast yeast nutrient, it does wonders for getting your yeast jacked!

One more thing. If you haven't checked your water, you could be low in Calcium. Maybe try adding 1 tsp of gypsum to your mash next batch. You want a minimum of 50ppm of Calcium.

Cheers!

I did aerate the wort before pitching and I live in San Diego CA so the water is AOK. I think I will try rousing the yeast and raise the temp a few degrees and get a reading in a few days. Thanks for all the advice, I really appreciate it.

+1 on warming it up and rousing it up.
At this point, no worries on warm temps. In fact, the yeast will work harder cleaning up after themselves.

Chances are you will still have some fermentation over the next few days but one of the biggest culprits in under-attenuation is not fully aerating your wort before pitching yeast.

During the later stages of any fermentation where your gravity has made a sizeable leap in a short span of time such as your case of 1.071 to 1.023, the easier fermentation work has just been completed at this point which is what you witnessed with the vigorous airlock activity in the first few days. Now the harder work for the yeast has begun where they have to break down more complex sugars. This process is slower and there is less CO2 being released which is why the airlock show intermittent activity. So just because your airlock isn't bubbling like crazy doesn't necessarily mean the yeast aren't working to further ferment.

If you only pitched 4 days ago don't do anyting, just let the yeast do their thang. The OG and pitching rate is an issue but nothing to worry about. I say do nothing just yet and take another reading in 7 days time.

You may even want to bump up the temp then just to make sure things are done.

I generally let my primary go for at least 2 weeks (with ales before I take the readings if there is activity in the fermenter.

I also wear no pants during the Sunday Sho and roll commando on weekends. Just sayin'

love

g