I like to drink both espresso and cappuccino.
Recently I have been playing around with dosing in my silvia - using a rocky grinder (ranging from 12g to 16g in the standard silvia basket). I have been splitting each shot so I have an espresso - which i drink while waiting for the boiler to get to steaming temperature and a cappuccino.
I have noticed two trends emerging.
1. I find a flat dose (overfilling the basket leveling off and then tapping the grinds down) - around 14g - is my least favourite dose. It seems no matter what I do there is more initial bitterness to the cup and is quite bright in a milk based drink.
2. A short dose 12-13g is slightly more acidic and seems to lack body (as compared to higher doses) in its espresso form but with milk the acidity is negated - from the sweetness of the milk I presume - and it appears to bring more body to the drink. :-?
3. A longer dose 15-16g seems to have less initial acidity and more body in espresso but a slightly (not bad) bitter aftertaste (back of the tongue) but this does not carry through to a milk based drink - tastes fairly flat. :-?
What I was wondering is if anyone could suggest why even though a larger dose has more body black it has less in milk and vice-a-versa for a low dose?
All of this was done with fresh beans - roasted 24 hours before they were bought and have been resting for a couple of days since then - from cafe pronto. When served in the cafe as an espresso it is quite bright and acidic (not bad).
(I presume youre keeping the extraction time similar in each case?)
I would suggest that the sensation of body in the cappuccino is an illusion, since body really comes from the creaminess of the milk (which, itself, can be illusory). So, it might have to do with the different types of flavours you are experiencing. I dont know the coffee you are using, but the higher doses can lead to underextraction, dulling down the taste and adding dull bitters. You could also try playing around with the temperature, though, to see if you can flatten the bitterness. The Rocky will tend to be best with lower doses, it seems, and this will also make the shots sweeter, lighter, clearer and brighter. However, there could also be less in the way of solubles, which will affect body. But, in higher doses, if they are underextracted, the solubles will be down, too.
Is the effect youre noticing consistent? I would still tend to think it is the type of flavour rather than real body, but I dont really know why.