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Ryan
04/05/08 08:40 AM  
New yeast pitching idea
Maybe not so new? I was thinking yesterday that homebrewers have an option that is not likely available to most commercial breweries. If the ideal yeast pitch results in 4 generations of growth before the primary fermentation really kicks in, but the more yeast pitched the safer/cleaner/ etc... the beer...

Could one pitch a small amount of yeast (say 1/4 of a starter) and let it go for about 4-6 hours and then add the rest of the starter? I'm thinking this would result in greater ester production but the larger second pitch would get things ramped up quickly thereafter.

Al B
04/05/08 09:18 PM  
Re: New yeast pitching idea
I'm not sure thats the way to go Ryan....unless the other 3/4 of the starter is still being aerated and growing nicely. I only say this because other factors influence ester production such as total pitch, aeration levels, amino acids, and temperature. You may be receiving more esters than ya want (and other off-flavors?).

Ryan
04/06/08 07:36 AM  
Re: New yeast pitching idea
Hey Al-

thanks for the response. The starter was on a stir plate and was just churning away. I had added pure 02 and nutrients, so the conditions you outlined are all met.

The reason I Thought about doing this is that my lag times have been under an hour for my last 5-6 batches and I know that that is not necessarily a good thing. SO I figure I must be over-pitching. I thought one way to account for that would be to do this double-step pitch.

I've used the pitch calculator on mrmalty.com but I guess it is just impossible for me to interpret was thin vs. thick slurry might mean and how to make cell counts per ml. without using a scope (which I am not want to do at home on a weekend).

Al B
04/06/08 12:13 PM  
Re: New yeast pitching idea
Pitch count can get alittle monotenous - and technical. Some articles lately describe underpitching SLIGHTLY for belgian strains as growth w/ O2 plays a role in flavor/ester production (Belgian strains). Getting to know a particular yeast strain and practicing consistency is alot of brewing.
Baums
04/07/08 11:01 AM  
Re: New yeast pitching idea
Hey Ryan,

You said "If the ideal yeast pitch results in 4 generations of growth before the primary fermentation really kicks in...", which I think is a misunderstanding (a very common one that's maybe even made its way into some homebrewing books).

The 3-4 generations of growth don't happen before the primary fermentation really kicks in--it actually happens as the yeast ferment the whole batch. As the old brewing scientist Karl Balling found, under "average" conditions about 5% of the sugar the yeast ferment gets turned into new yeast cells (the rest goes mainly to alcohol and CO2 of course), and this happens pretty much continuously.

For an average batch pitched at average pro rates, this 5% turns out to be 8-16 times the initial yeast mass (which is 2^3 or 2^4, or 3-4 generations). You can actually do the math using Balling's 5% ratio and assuming a pitch rate of 1M cells/mL/P, and that 20B cells of yeast weigh 1 gram, and see that this is true.

(One source of the intitial confusion are the plots in various books--I think there's one in Papazian's--that show suspended yeast cell count as a function of time. But these plots don't tell the whole story because they don't account for the yeast that's piling up on the bottom of the fermenter...)

As for esters, if you want more acetate esters (isoamyl = banana, ethyl = pear/solvent, phenylethyl = rose) then it's easy--just follow the exact same practices you have been, but cut your pitch rate by some amount (maybe try a 25% reduction to start, or 50% if you're brave). No question this should work.

The other kind of esters in beer (other than acetate esters) are ethyl esters, and controlling these is harder--it's a current area of research at KU-Leuven. They are not regulated by the same enzymes and processes as the acetate esters. Where acetate esters are tied to (reduced) yeast health at the end of end of fermentation when the yeast run out of gas, ethyl esters (ethyl hexanoate = apple, for instance) are not. They seem to be produced at a more constant rate, and I believe the best current advice for increasing these is to increase temp and/or specific gravity.

And along the lines of what Al said, none of this means jack if you change the yeast strain at the same time. For that matter it may even be next to worthless if you make major changes to the recipe. It's more useful for fine-tuning a recipe once it's already pretty close to what you want.

Oh yeah, for a continuously aerated 1.040 starter 100B new cells per liter of starter is a good guess.

Ryan
04/07/08 11:31 AM  
Re: New yeast pitching idea
Thanks Baums

Given everyone's trepidations, I eventually decided not to take this approach. Rather, I under pitched. I decided that since my starter was really blasting away, had been oxygenated and on a stir plate for two days, that the yeast were healthy.

I only pitched about a third of the yeast. The lag time was closer to 8 hours and it was two days (not till this morning actually) before I had blow off. Now things are going nuts in there. I am fermenting a trippel with WY3787 which is purported not to make much in the way of iso-amyl acetate, but it smells like a chaquita factory in my bathroom this morning (oh and there was yeast on the floor and walls...).

Seanywonton (Sean White)
04/07/08 12:03 PM  
Re: New yeast pitching idea
What kind of pitching temp are you normally doing? If you were too hot, that could account for a lesser lag time too.
Baums
04/07/08 12:18 PM  
Re: New yeast pitching idea
Do you know what your pitch rate was (assuming you got 100B cells per liter of starter)? The last time I used 3787 (a tripel also) I pitched at about 1.4 M cells/mL/P (first few days of ferment at 66F) and the ester levels were pretty low which (not surprising).

BTW you can get more iso-amyl acetate than normal, if the yeast first produce more isoamyl alcohol than normal. 3787 can definitely produce this and other fusels in abundance. Primary ferment temp, and FAN levels, are two variables that matter there. (Too little or too much FAN should give lots of fusels. Moderate FAN should minimize them.)

Ryan
04/07/08 01:15 PM  
Re: New yeast pitching idea
Sean: I probably pitched about 67 degrees. My other batches have been warmer (high 70's).

Baums: I figure I pitched about 50B cells (300 mls of a starter that was about 2.5L of total wort (decanted the first half after about ten days and then added a liter of fresh wort and put on a stir plate).

I figure this is about half of what would be optimal given the 1.08 OG.

Baums
04/07/08 03:24 PM  
Re: New yeast pitching idea
Well, 1.080 OG is 20P, so if it was a 5 gallon (19L) batch the US pro rate would be 380B cells, while the lowest reported pitch rate in BLAM (from Rochefort I think) would be about 190B cells.

While stir plate starters (with loose tops for continuous aeration) should make about 100B cells/L, if you're not continuously aerating then the numbers I've seen are more like 35B cells/L. Maybe I'm mistaken (and guessing) but it sounds like your starter procedure was like this:

1. start with Wyeast XL pack (100B cells or maybe less, depending how old it was?)

2. make 1.5L starter NOT continuously aerated(grow about 50B more cells)

3. decant spent starter and propagate into 1L of continuously aerated wort (grow about 100B more cells)

for a total of 250B cells, or 0.63M cells/ml/P. Sound about right? In this case I think you're at the low end of what might be used for some strains in Belgium. I'll be interested to hear how it turns out, especially cause I've decided I want to mess around with 3787 more myself.

Ryan
04/07/08 03:43 PM  
Re: New yeast pitching idea
I pitched a smaller smack pack (propogator) into 2L, not continuously stirred but to which I had added o2 (i left town).

Then I decanted and added to another 1.25L with 02, yeast nutrient, and continuously stirred (loose top).

I don't see how you got 250B cells though. 20P * 19L (19000ml) * 1.4 =53B no?

What am I missing?

Baums
04/07/08 04:08 PM  
Re: New yeast pitching idea
I think you're missing a factor of 10 somewhere... 20*19*1.4 = 532. (?)

It sounds like you started with a Propagator pack (25 B cells) and put it into a once-aerated 2L starter (growing about 2*35B = 70B more cells). Then propagated that into a continuously aerated 1.25L starter (growing 125B more cells) for a grand total of 220B cells?

(plus or minus 20% or more, cause all these numbers are approximate...)

Anyway, I liked the beer I made at 1.4 M/ml/P a lot, but I want to see if I'll like it more with a few more esters. I may try about 1 M/ml/P next time. You're around 0.6 M/ml/P, which I suspect might be dabbling with the lower limit, but then again it might not be--anyway I think you'll get the increased esters you're after.

Ryan
04/07/08 06:35 PM  
Re: New yeast pitching idea
Add to that the fact taht I only pitched about 1/2 to 2/3 of the yeast cake and I'm way down there, but its churning away like made and that lag time wasn't terribly long (6-8 hrs ish).

I'll certainly let you know how it turns out and I'll likely re-brew this with a bigger pitch to see the effects with this yeast.

I have found that Abbey ale II is pretty tolerant to different pitch rates.

Baums
04/08/08 09:53 AM  
Re: New yeast pitching idea
Oh yeah I forgot you only pitched a fraction of that. Thought you said 300 mL but maybe it was the thicker part of the starter.
Ryan
04/08/08 09:57 AM  
Re: New yeast pitching idea
I don't know why I wrote that bit about abbey ale 2 since I'm using 3787 on this go. I guess what I was noting is that the other strain I've used a lot is prety tolerant so this one might be too?

I usually make starters from the yeast dregs from a previous batch. If I dump a small bit of slurry into a flast of fresh wort and then put that on a stir plate is there a quick way to calculate yeat abundance?

Baums
04/08/08 10:58 AM  
Re: New yeast pitching idea
Well like I said 100 B cells per liter is a decent guess for the new cells you grow on the stir plate. But I don't have a decent estimate for how much you start with in a given amount of yeast cake. I HAVE seen numbers for that, though, and a web search should turn them up. Problem is how dense your particular yeast cake is vs another...
Ryan
04/08/08 11:49 AM  
Re: New yeast pitching idea
exactly

density...

what is a thick vs. thin slurry

 
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