Butter scotch taste

[rathskellar]

I brew all grain and extract. Why do I get butterscotch taste sometimes with all grain but never with extract? Example made a Blonde in full grain and another in extract, same recipe and fermented side by side. Again all grain butter scotch but with the extract. Confused.

[jawbox]

Sounds like diacetyl. It would give a pronounced butterscotch flavor in high enough concentrations.

[slothrob]

One possibility I can think of is that your water is lacking some trace mineral (zinc, maybe?) and stressing the yeast. The extract contains the minerals from the mash water used by the manufacturer which may be supplying this need. You could try adding some Servomyces yeast nutrient and see if it solves the problem.

Another possibility is that you're contaminating the brewing area with grain dust and getting a diaceyl producing microbe in the beer.