There's probably no more tired yet important topic- how to manage a shot. I read Jim Schulman's excellent article: The Home Barista's Guide to Espresso. What got my attention was about ending a shot by color. But it seems that more baristas go by weight. Weight is precise and color is very subjective. Do people use color and if so, how reproducible are your results? Thx!!

I used to go by colour and sometimes by volume. I now nearly exclusively go by weight. I do watch the colour though; if it blonds early, then there is likely something wrong (old coffee, grind, temperature, preinfusion length...

Jim's article gives excellent advice for its time:

Time the shot, and run it into a cup from which you can tell the volume. Stop the shot when the flow lightens to "blonde," a tan color showing some transparency. This flow color indicates that the proper amount of coffee has extracted, about 20% of the puck. Try to get into the middle of the acceptable range: 1.5 to 1.75 ounces in 25 to 30 seconds. If the shot takes longer, or delivers less volume, grind coarser; if it delivers more volume or happens in less time, grind finer. More precise adjustment requires tasting shots and diagnosing them. This is explained in the next section.

Back in the day, the generally accepted practice was extraction by volume or color. That's what I used to do: extract until the shot blonded (which typically resulted in shots with a brew ratio of ~2:3). But volume is imprecise due to variation in crema, and blonding is subjective.

Andy Schecter's wonderful post on brew ratios made a fundamental difference in the espresso community. Nowadays, dosing and extracting by weight is far more common. For a given coffee dose and brew ratio, the extraction amount (liquid weight in the cup) is predetermined.

The good news: ground coffee dose is more critical than amount of extracted liquid. So I always weigh my dose, but sometimes extract by volume (or color) for convenience. Once dialed in for a specific bean/grind/basket/coffee dose, the volumetric dosing on my espresso machines seems good enough for daily driving. But when dialing in or testing, I always weigh both dose and extraction to achieve my target brew ratio.

I found volume in the cup to be a very poor method, as far as repeatability goes.

I use visual clues, color changes throughout extraction, shape of the pour, coalescing and thinness of the stream, a "bell" at the basket, as clues about grind, prep, and length of extraction. Going with visual only, my notes show around a 5-10 g window. On 30-40 g, that's not very tight.

With a machine that is very repeatable with at least temperature, PI volume and resulting flow rate during extraction, I get very repeatable taste and texture going with weight in the cup once a coffee is dialed in.

In a commercial setting, volume in is "good enough" for repeatability. Volumetric metering is part of many commercial machines, or is closely approximated with a timer.

On the other hand, a skilled barista using a manual lever can get fantastic results varying the pressure based on the look of the pour alone.

Jeff wrote: a "bell" at the basket

I get a bell shape at my basket pretty often. What does that generally tell you about the brew? Seems to happen more with lighter roasts for me and I haven been able to get rid of it.

I often find that lighter roasts require a finer grind, higher temperature, and "more water" to extract to my taste than comfort blends or darker "espresso" roasts. They tend to look less viscous to my eye during extraction. For me, it's not so much the bell itself, but the changes that I take note of.