Imperial A09 Pub - don't oxygenate for maximum diacetyl

[Mer-man]

For giggles, in lieu of a proper fast ferment test, I pitched some wort with a massive pitch of A09 - but unlike the main batch, did zero oxygenation.

Butter-scotch Mountain. It also finished several points above the main batch.

The main batch, not bad. Just English character.

I'd heard that English strains need more oxygen, hence the historical practices of double dropping, open fermenters, rousing, etc. But take this as a single data point warning -- unless you like butterscotch!

 

[Mer-man]

Following up, nobody should try the CYBI Union Jack recipe with A09. Use a Whitbread strain at least. This Pub/Fullers crap is not suited for hop heavy beers

 

[RPh_Guy]

massive pitch

High pitch rate increases diacetyl.

See here:
https://onlinelibrary.wiley.com/doi/full/10.1002/jib.84

 

[Mer-man]

Yeah, so rather than seeing the effect of not oxygenating, I made a diacetyl sample. Haha - thanks dude.

 

[Vale71]

High pitch rate increases diacetyl.

See here:
https://onlinelibrary.wiley.com/doi/full/10.1002/jib.84

And so does increased oxygenation. In general anything that promotes yeast replication will lead to higher diacetyl levels.
IMHO the most common cause of diacetyl issues with homebrewers is dropping the temperature too soon, too far and too fast thus negatively affecting diacetyl reuptake by the yeast.