I have tried adding bicarbonate to the espresso and it makes a massive difference. I used to add a tiny amount of sodium bicarbonate and magnesium on top of the puck screen as I was under the impression that they are required to enhance extraction. However my experiments have shown that it is possible to achieve the same results by adding the minerals to the espresso.
I live in Manchester where the water is very soft. I use tap water in my machine (please don’t judge) as I do not think scale will be that much of an issue. I never see scale in the kettle that is used several times a day. My coffee machine is used 2-3 times/week..
These calculations might be way off. Please correct me if I am mistaken. I find it quite difficult to understand these water calculations.
According to the water services, the average alkalinity of the tap water is 17.5 in terms of CaCo3. I used Rob1’s calculator to estimate the amount of bicarbonate required to produce alkalinity of 40 which was 48 mg/litre.
I then used the calculator to determine the amount of sodium bicarbonate required to achieve this level of bicarbonate. To produce a 50 ml concentrate we need about 0.1 gm of bicarbonate of soda in 50 ml of deionised water. Adding 1 ml of this concentrate should elevate the alkalinity of a 30 ml solution (average espresso volume as I use 15 gm coffee and generally a 1:2 ratio) to 40mg/litre.
Adding 1 ml of this concentrate made an improvement to the taste. Adding 2 ml made more of a difference. The espresso was less harsh, more rounded, sweeter and complex. I tasted the espresso before and and after adding the bicarbonate. The difference was obvious with 2 ml.
I appreciate this method is far less accurate than making your own water.