When I read you should try 1:1 , 1:2 , 2:3 to taste the differences, if my dose volume is fixed be it 7grams for example; should I keep coffee grind or extraction time fixed to achieve the desired volume?

I also understand the Italian standard for a single shot normals is 7grms, 21 millilitres in 25 seconds. This is 1:3 and I understand to be technically a Lungo. Is a 1:1 risteretto 7 millilitres?

Firstly, singles are much harder to pull, and 7g singles in particular. I highly recommend mastering your double basket before you mess with singles.

Secondly, these ratios are in terms of weight. 1g of water has a volume of 1ml, but espresso volume is highly variable because of dissolved CO2 and crema. A 7g espresso shot is going to have a volume greater than 7ml.

Finally, the answer to your actual question is: it depends. Leaving your grind unchanged and simply letting your shot run longer to get more output is a legitimate experiment that can yield good results. But there is no one size fits all rule. You basically have to experiment with the entire parameter space and see what works. Be sure to read Jim's guide here: Espresso 101: How to Adjust Dose and Grind Setting by Taste

Taking it further then, does using bottomless vs single vs double portafilter impact time? I appreciate the guidance in the 101 suggests going by taste and weight over time.

I pull 7.5g, 3:1 singles at my coffee bar. I have to grind finer than my 15.5g doubles to get them to run the same 28s. I use bottomless portafilters unless I get multiple single orders. Then I split doubles with the double portafilter.

Matt Perger's video covers your exact questions.
http://www.youtube.com/watch?v=-BT7-yOUMDM

myso wrote:Matt Perger's video covers your exact questions.
http://www.youtube.com/watch?v=-BT7-yOUMDM

What a great video and working example. Thanks for this.