[Homebrew_kev]

does that affect flavour?

For the most part, i don't think it would.

but

If you had designed a recipe for 80% BH efficiency and it ends up at 40% - then yes, I imagine it would affect the flavor.

But If you''re shooting for an OG of 1.055 but it comes out 1.035 - then that could be an issue. Although, if you're shooting for 1.085 and it comes out 1.065 - the finished beer won't meet your expectation, but it's probably still pretty good.

[denny]

I believe a wider gap does add to the beer. I only have my anecdotal brewing experience to rely on for this statement.

I intentionally opened my mill gap to increase the grain bill as well as increased mash duration to account for the larger grits when I began brewing lower ABV beers. When I was crushing finer to get the same OG the beers came out thin.

Based on this experience I believe there’s more created/extracted in the mash than just sugars converted from starch.

Counterpoint...for nearly 25 years, my mill has been set as tight as it will go. I have never noticed "thin" beer. My only point is that people can't generalize based on either of our experiences.

[chinaski]

does that affect flavour?

For the most part, i don't think it would.

but

If you had designed a recipe for 80% BH efficiency and it ends up at 40% - then yes, I imagine it would affect the flavor.

But If you''re shooting for an OG of 1.055 but it comes out 1.035 - then that could be an issue. Although, if you're shooting for 1.085 and it comes out 1.065 - the finished beer won't meet your expectation, but it's probably still pretty good.

I think if the efficiency decrease was solely due to particle size in the mash, then the flavor wouldn't be all that different especially if there aren't a lot of specialty grains.  If the efficiency decrease was due to other factors, temperature, pH, etc. then you are more likely to have flavor differences.  I think this because I'm guessing that with particle sizes being larger, the enzymes can't access the starches as readily.