Attenuation in big beers.

[Dave70]

I'll be doing a slightly tweaked version of Brewdogs Old world RIS shortly and the recipe calls up for Wyeast 1272. The beer finishes at around 9.5% and the ABV tolerance of the yeast is shown at 10%, which seems to be sailing a little close to the wind.
In general my beers never go any higher than 5.5% with a 2L starter and good temp controll, so under attenuation isn't an issue. However the last beer I remember dumping was a disastrous 10% Belgian dark that seemed to come out of the fermenter much the same as it went in, even after a month.
Any tips or methods for helping the yeast along its way? Bigger starter? Starting cold and ramping up the temp? ???

{edit -speeling}

 

[Yob]

2 x 2lt starters at least, (start the second off the back of the first)

4-5 mins with a paint stirrer for aeration..

repeat at 6 and 12 hours if you can, definitely at 12 hours...

my last RIS, (1.135 OG) was finished in 7 days on this method (1275) and got over tolerance (%10) which I was pleased and surprised about. I had a cake ready to throw it on to finish off but just left it in the end.

 

[eldertaco]

Agreed on the re-oxygenation after pitching, it seemed to work really well on the last belgian I did, and got fermentation off to a crazy vigorous start.

I did it twice, at 4 hours and 8 hours, went to bed and the next morning it was going absolutely mental. After a few days it had slowed right down and looked like stopping at 1.020 so I started to bump the temperature up by a degree or two a day and it ended up finishing at 1.008. Then again 3787 is a hungry beast.

 

[Lyrebird_Cycles]

Watch the temperature at the end: warm is good, too warm is very bad.

This is because the lipid bilayer in the yeast cell wall is a liquid crystal which has a melting point and alcohol toxicity increases markedly above the melting point.

The melting point is dependent on lipid makeup, which in turn is dependent on strain, nutrition and oxygen (amongst other things). Oxygen in the growth phase increases ergosterol synthesis, ergosterol stabilises the cell wall raising the melting point and thus improving alcohol tolerance. Two O2 saturations 12 hours apart as suggested above sounds like good practice to me.

Similarly a large pitch reduces the number of doublings the yeast must do which reduces the dilution of ergosterol. In the absence of oxygen the yeast can still reproduce but it can't make ergosterol so every time the yeast buds it must spread the amount of ergosterol it has across two cell walls.

 

[Dave70]

Cool. I recon this wouldn't be a bad way to go either.
As luck would have it, I just happen to have a brand new stick blender. With plenty of warranty left.

https://www.youtube.com/watch?v=cqM_rpXTk7A