I just did a bit of research and it seems they do it with a printer! The company says the colour extracts are odourless and flavourless, the brown ones are made either from coffee or malt extract which would be a similar flavour profile than Guinness, and (a bit of educated guessing from the top of my head) I would put the quantity of ‘ink’ in these prints in the tens of micrograms, like 0.01-0.1 mg. I think the flavour and aroma wouldn’t be affected.
I just did a bit of research and it seems they do it with a printer! The company says the colour extracts are odourless and flavourless, the brown ones are made either from coffee or malt extract which would be a similar flavour profile than Guinness, and (a bit of educated guessing from the top of my head) I would put the quantity of ‘ink’ in these prints in the tens of micrograms, like 0.01-0.1 mg. I think the flavour and aroma wouldn’t be affected.