I'm trying to make sense of a Stout recipe and one of the ingredient is:
1.00 Coffee Espresso Shot
Now, according to Wiki, one espresso shot is 25ml. Would this be the right amount for a 23L batch size?
The size can be a single, double, or triple, which corresponds roughly to a 0.8, 1.7, and 2.5 US fluid ounce (approximately 25, 50 or 75 mL) standard (normale) shot, and use a proportional amount of ground coffee, roughly 7, 14, and 21 grams
I don't see any way you could know for certain. IMO, the best way to add flavoring to beer is by taste. Wait until the beer is fermented and pour 4 2 oz. samples. Dose each with a different, measured amount of espresso and taste to determine which you like best. Then scale that amount up to your 23L batch size. I do this with every flavoring I try and it's a very easy, effective and accurate way to determine how much to use.
25ml is incredibly small in proportion to 23L. Imagine pouring an espresso shot into 1 liter of your favorite stout (think 2 full pints). You would definitely taste that, and it would probably be described as a bold coffee flavor, but probably not even overbearing. Now imagine that flavor but 23 times weaker. It would be subtle or gone entirely.
To answer your question, IMHO, a shot of espresso is 1 fluid oz. I would think this significantly too little espresso for 5g unless you are looking for a very delicate flavor.
More generally about espresso: In addition to D.C.'s sensible answer, I want to add that you can do whatever you want with coffee/espresso and it will probably work out at least ok. I have added espresso to all phases of brewing from wort to primary fermentation to secondary to bottling in all forms from grounds to shots to cold toddies. The advantage of after fermentation is control of flavor. The advantage of shots is no grounds. The advantage of just chucking in a 1 lb of espresso while boiling the wort is ease (for the record, that flavor will not be 'delicate' but coffee drinkers will probably like it). About the only thing you can do wrong is leave your bottles of coffee stout aging. The coffee does not, in my experience, improve with time.
For my last espresso stout I was unsure of how much to use. I opted to add varying levels, from about 1/3 of a shot per 12oz bottle up to a full shot per bottle. 1/3 of a shot was noticeable but mild and a full shot was quite pronounced but still not overwhelming.
Given there's a lot of variables (the flavor and strength of both the beer and coffee) I'd suggest you try the same. If you're adding at at bottling time (I did) then you can take a small sample of your finished beer and experiment with what concentration you'd prefer, or as I did you can make several sub-batches of varying strength.
