Promoting ester formation - temperature, aeration, pitch rate, etc.

[thecebruery]

So I'll be brewing a 1.069 Belgian Dubbel soon with the new Safbrew Abbaye yeast this week. This thread has a nice collection of peoples' results and opinions, but a few things seem to be common to all (or at least, most): a) it's a sulfur bomb but that it cleans itself up in time; b) it attenuates like a beast (83% - 93%); and most importantly to me, c) it's pretty mild, or that it tends towards the phenolic rather than the estery, though it does seem most people in that thread fermented on the cooler side of things (I see a lot of 62F - 65F fermentation temps).

My goal is a balanced Dubbel with a lot of yeast character. The recipe I'm using is about 70% pilsner, 10% caramel aromatic (20L), 10% munich, 8% amber candi sugar, 2% Special B, and a hint of chocolate thrown in to the mash late for color. I'll mash at 154F.

Before anyone says it, I'm in the Philippines, so running down to my LHBS for a vial of WP500 is out of the question. And yes, I've even tried propagating from bottles of Chimay Red - by the time they make them over here, the bottles are a year or two old and the yeast are dead dead dead. So short of paying $150 to FedEx in a vial on ice (which I'm not prepared to do - yet), this 500g brick of Abbaye will have to do me.

With the production date on my brick of last March, Mr. Malty estimates 68% viability, and suggests 176 grams of dried yeast for 1.6 barrels of 1.069 wort.

I'm thinking I'd like to gently stress this yeast to encourage it to produce esters. Though there are plenty of threads that talk about it in general terms, my question to y'all is about facts and figures.


1) When you underpitch to encourage ester formation, how much do you underpitch by? 25%? 50%? Safbrew's data sheet for Abbaye suggests 50 to 80 g/hL to pitch, and 1.6 barrels is 1.91 hL, or a range of 96g to 153g, perfectly in line with Mr. Malty's recommendation assuming 68% viability. Would hitting something about 100g (near the low end of the manufacturer's suggested range) be ok? 17 plato and 191000 mL of beer with a pitching rate of 0.75 million cells/mL/P is 168g ... but this article says Westmalle has a pitch rate of 0.25 million cells/mL/P and Duvel a pitch rate of 0.44 million cells/mL/P. Has anyone had success pitching at around 0.25 million cells/mL/P (which would be only 56g of 68% vitality yeast)?


2) When you ferment high to encourage ester formation, at what temperature do you pitch, and how fast do you let it rise to what temperature? Safbrew's data sheet for Abbaye gives a temperature range of 12-25°C, or 53.6-77°F, and an ideal range of 15-20°C, or 59-68°F. I have deep thermowells and a homemade glycol chiller of several HP that can knock temperature off no problem, so I'm not going to overshoot anything. The same article mentions Duvel and Westy both pitching low (~64F) but then letting them free rise up to as high as 84F over the course of five days. Has anyone had success letting their Belgians rise this high? What fermentation schedule did you follow? Did you do this in lieu of or in conjunction with underpitching?


3) When you aerate less to encourage ester formation, at which flow rate do you add oxygen/air to your chilled wort, and for how long? Normally, I aerate at around 3 L/min - should I cut this in half? By 75%?


I know this is a tricky question - this yeast is very new, and every yeast behaves differently - but I'm hoping that the collective wisdom of this board will help generate some guidelines about numbers to never go beyond, or good starting points.

 

[tagz]

I tend to worry about fusel alcohol production so I've always been hesitant to stress out yeast by under-pitching. Personally I would pitch a healthy amount and focus on temperature to achieve your desired profile.

 

[grathan]

Dry yeast is tough to coax ester from lack of aeration. Why not shoot for ester production on a repitch?

 

[thecebruery]

Dry yeast is tough to coax ester from lack of aeration. Why not shoot for ester production on a repitch?

That's a fair point. You think it'll be easier to manipulate on the first generation after harvest?

 

[grathan]

I think you would have more control. I have never repitched dried yeast before. But you don't really know the sterol reserves built into the dried yeast on the first pitch.

I think underpitch the first batch. Re-use for second batch and skip aeration. There is a decent thread here on this yeast, some people reporting bubble gum and phenols depending on pitching temperature. I am not a fan of raising initial ferm temps due to higher alcohols forming. I would start mid to upper 60's and then let it raise up into mid 70's-80s pretty much the 1st/2nd day. This will also help with diacetyl cleanup which will be necessary if you don't aerate. I've never used this yeast, but all yeast seem similar enough.

 

[thecebruery]

I think you would have more control. I have never repitched dried yeast before. But you don't really know the sterol reserves built into the dried yeast on the first pitch.

I think underpitch the first batch. Re-use for second batch and skip aeration. There is a decent thread here on this yeast, some people reporting bubble gum and phenols depending on pitching temperature. I am not a fan of raising initial ferm temps due to higher alcohols forming. I would start mid to upper 60's and then let it raise up into mid 70's-80s pretty much the 1st/2nd day. This will also help with diacetyl cleanup which will be necessary if you don't aerate. I've never used this yeast, but all yeast seem similar enough.

Due to the difficulty of obtaining yeast here, I'm harvesting everything I pitch, so I'll definitely be using this one again (even if it sucks, unfortunately - I'll just keep tweaking it until I make it work). So reusing and seeing if minimizing aeration on the second generation works is doable.

If Mr. Malty suggests 176 grams (and a pitching rate of 0.75m cells/mL/P), do you think a pitching rate more in line with some of the sources I linked to (say, Duvel @ 0.44m cells/mL/P) would be a good place to start? That's 103 grams of dried yeast, or 58% the "recommended" dose.

 

[grathan]

You really gonna make 1.6 barrels of a recipe and yeast you've never tried? I'd say try the 103 grams. It's not a perfect science measuring old dried yeast.

 

[thecebruery]

You really gonna make 1.6 barrels of a recipe and yeast you've never tried? I'd say try the 103 grams. It's not a perfect science measuring old dried yeast.

Heh, it's the size of my system. The grain bill is one I've used many times before (with a few minor tweaks), so I know and trust the wort. I suppose I could do a pilot sized batch in a bucket (there's no such thing as a glass carboy where I am), but I'd have no ability to do any sort of reasonable temperature control on it, so the validity of any results would be questionable at best. Thanks for the input!

 

[madscientist451]

If you haven't already seen this, here's a pretty good source of information about esters using Belgian yeast:

http://byo.com/hops/item/636-fermenting-belgian-style-beers

I've also been studying open fermentation, but haven't done it yet with beer, it is reported to increase ester production.
If you are saving your yeast, open fermentation and top cropping the yeast may be something you want to try.

 

[RM-MN]

This article might be of interest to you as the author explored both over-pitch and under-pitch compared to a "proper" pitch. Note the amount of over and under pitch. http://sciencebrewer.com/2012/03/02/pitching-rate-experiment-part-deux-results/

 

[thecebruery]

Thanks to everyone - I pushed this brew back a few days so I could spend a little more time thinking/do a little more research on this issue, but I'll be brewing it Sunday.

I think I've decided to underpitch slightly (say, 0.56 million cells/P/mL, which is 25% under the "recommended" 0.75 million cells/P/mL), under-aerate slightly (say, at the same flow rate, but for only 75% of my knockdown period, or about 22 minutes out of my typical 30 minutes - I run medical O2 in-line through a 2 micron sinter stone welded in to a tee-joint on the cold side of my plate chiller), and pitch around 65F but let it free-rise up to 75F and then keep my glycol chiller on it to hold it between 73 and 75F. At my ambient that should probably take a day or two, so it should be in the throws of fermentation by the time it reaches that apex, particularly since I've read this one's a fast starter.

I think this is a restrained approach, not pushing the yeast too hard in any one particular direction. I will, of course, report back once she's done and ready to drink. Thanks for the input!