Why I preheat my portafilter when making espresso

I'm trying to dial in my espresso with more accuracy. When I started, I just used the default auto two shot button and let the expresso pour. With this method sometimes it was great and sometimes it was terrible. The espresso was never consistent, so I went down the rabbit hole of manually pulling shots. On this journey, I discovered that pulling a cold portafilter shot was completely different than pulling a warmed portafilter shot.

This blog post is about how you should warm the portafilter before pulling espresso shots. I'm usin gthe Breville Barista Pro espresso machine (in blue if you are interested).

This all started when I was dialing in Verve Streetlevel roast. At first, I was doing it with a cold portafilter and not getting smooth shots. The grind size was 14 on the built in grinder. The first shot was bitter and poured way fast. It came in under 20 seconds. So, I'd adjust to grind finer to a 12. However, the second pull took 46 seconds and it was clear that it was clogging up.

Then it occurred to me that I had read someone saying to heat your portafilter before pulling that first shot. A throw-away shot as they called it. Then it clicked and it all made sense. I wasn't comparing two comparable shots. A cold portafilter against a warm portafilter is going to act totally different.

Why should you preheat the portafilter?

By using a cold portafilter, the portafilter draws heat away from the brew water on contact. This drops your brew temp immediately. Lower temp means less extraction and can cause sour tastes.

If the cold portafilter is causing less extraction, then you might be tempted to change grind size to try fixing the extraction. One grind size on a cold portafilter will produce a significantly different coffee than on a warm portafilter. You can't accurately dial in if this variable is in flux. This will cause you to spin your head until it falls off because nothing makes sense anymore.

So that's why I warm up my portafilter by pulling an empty shot first. This sets the baseline temp so everything after will be consistent. The temperature changes the flow and fast water moves through the puck. If time is a measurement, we won't get the same time from one shot to the next—even when the grind is the same.

My process now

Now that I'm warming up my portafilter before I pull my first shot. Here is my new routine when dialing in espresso.

Put portafilter in the group head

Run an automatic single shot through the empty portafilter into espresso cup

This warms the portafilter and warms up the cup

Remove portafilter

Use WDT tool to separate grounds

Tamp & put into group head

Run a manual double shot by holding down the double shot button for 8 seconds pre-infusion. After 8 seconds let go.

Let run until I reach 34 grams of liquid. I'm going for 1:2 ratio as the baseline to start. The last two grams will flow after letting go of the button.

Hopefully I end up with 36-40 grams of espresso in 25-30 seconds. If the time is less than 25, grind finer. If it's more than 30, grind coarser.

Repeat until I find a taste I like and the time is somewhere in that range of 25-30.

Now I've started preheating my portafilter and can work on a level playing field as I move through my coffee brewing journey. I look forward to applying these lessons on my next couple shots to see if I can dial in at Street Level. Once and for all.