Hi guys, I'm fairly new to the home barista setting and am, for the most part, enjoying myself. The issue is the last few days I've been getting fairly slow shots that are pretty darn sour. They hit strong then mellow out into a flavor I'd like to be for fronting my espresso.

My setup is a Rancilio MD-50 ST grinder and Delonghi EC702 espresso machine. Shortly after I was given the machine as a gift, I got myself a handy bottomless portafilter to access my extractions. First few days were disastrous but I've finally gotten myself to a pretty even extraction. It's by no means great, but now that I've at least come that far on my own I've come here for help.

I'm using a 14 gram dose and pulling about 1.8 oz of espresso in 30 seconds. My current theory is that my machine is running on the cool side of things. I had planned to try brewing at a higher temperature the next time I did things and see where that landed me. Aside from that I'd just like any tips/advice that could be given to me concerning my setup and just anything that will help me out.

A few more notes for some questions that I anticipate. My beans are purchased from a local Cafe that roasts all their beans weekly. That being said I just picked some more up today so they are probably 4-5 days after roast. The owners weren't in the shop when I stepped in and I didn't ask their other employees for the exact roast date.

30 seconds is not exactly a slow pull. Kinda standard, imho.

Are you sure your beans are not underdeveloped?
And you're right it could also be too low temperature. If it's too hard to raise the temp, grind finer and pull longer. If that doesn't help, lower your dose, grind finer and you might even consider pulling longer than the previous longer...

Hello and welcome!

There is a sticky right at the top of this page - Espresso 101: How to Adjust Dose and Grind Setting by Taste

The idea of a sticky it's in the most obvious place the site admins can put a Hall of Fame thread. From my perspective, this thread is worth double the price of admission. Study and master this content and you're in espresso graduate school.

This particular thread squarely addresses your question. And, it goes further because it also explains why one can get a bitter shot. Sour and bitter are kind of the polar opposites in espresso - or I can say that from my personal experience, I've created bitter espresso and sour espresso, but never sour & bitter espresso. It's really easy to go too far, (ask my wife), and this will guide you to nirvana.