The better the machine, the more control and stability you'll have with water temperature.
Our machine, a Simonelli T3, is meant to stabilise at 0.2 degrees Celsiusover 15 shots. It has 14 pounds of brass in each group head to give it serious thermal mass and three temperature controllers per group to help keep the water within point two of a degree of a set-point temperature. For us this is usually around 93-94 degrees. So the more you spend, the more control you'll have.
A traditional Italian single shot is made with seven grams of coffee, and a little pod on averagecontains about five grams. The average dose in a speciality coffee shop would be more like 18 to 20 grams. We try to keep our dose within point two of a gram; a really accurate dose has been proven to improve consistency.
Also, make sure the coffee is evenly distributed, and tamped firm and flat to prevent 'channeling' or uneven 'washing' of the grinds occuring. The level of pressure the coffee is put under in a commercial machine is about 135psi.
3. Extraction time
Time is the only parameter you have control over with capsule machines because you can turn the button on and off whenever you want.
In general, with the light roasted, newly cropped coffee we use, our shot time is usually between 28 to 32 seconds. To produce a normal 25-35ml shot, extraction time with the average home pod machine is 12 to 15 seconds. This is because there's so little coffee in the average pod and the grounds aren't as fine as a barista would use.
It might be worth running shots a little longer on a pod machine to achieve better extraction yields at the expense of body. Which brings us to step four...
The parameter that most speciality coffee shops use to affect flow is the grind; if you have a courser grind, water will flow faster. We zone in on the optimum shot time by changing the grind. The optimum espresso is simply the most balanced shot with the best crema, the nicest flavour and the roundest, smoothest body.