Author Topic: first principles question on starters  (Read 577 times)

Offline dertiefster

  • 1st Kit
  • *
  • Posts: 5
    • View Profile
first principles question on starters
« on: August 03, 2013, 12:49:42 PM »
I would like to understand the difference (and underlying reasons for any difference) between pitching a single vial of yeast into 5.5 gallons of wort vs. taking a half-gallon of that wort and making up a starter, then pitching the yeast into the remaining wort.  I do not presently understand.  I'm a physicist and would like to be further educated in matters of brewery.

From what I have read, one might view the process as fencing off 10% of the brew volume, pitching the yeast vial into it, and then at some nebulous time later (at or after high kraeusen) removing the fence.  Somehow the confinement of the yeast (the only difference I can see) results in something different from simply pitching the yeast vial into the original wort volume.

My most recent batch (#8 after a 30 yr hiatus in brewing) was also my first >5 gallon batch.  I made up 11.5 gallons of 1.044 wort for a saison-like brew.  I diverted 1.5 qts into a half-gallon glass jar, pitched the very fresh vial of WLP585 saison iii blend into it, and watched it while I gathered the rest of the wort into a 15 gallon fermentation vessel.  Very few hours later the foam on the starter had risen to about 3", very nearly overflowing the starter vessel, so I pitched the whole thing into the 11 gallons of wort.  Within a few hours, vigorous fermentation had begun (which means to me that the wort had become saturated with CO2 so that the excess was bubbling out of it).  By the morning of the second day (75F ambient temps, no chilling of the wort prior to pitch -- it was just room temp) all signs of fermentation had ceased.  The sp. gr. measured 1.006, an apparent 86% attenuation in 40-ish hours.  In the few days since then, no further attenuation has been apparent, and the beer is holding 1.006.  This mash did not exceed 150F, so I expected to have a high fermentable fraction of sugars, but that appears to be a phenomenal fermentation rate for a single vial of yeast in 11.5 gallons of wort.

The use of a starter-like process with so short a starter growth period seems to me to be indistinguishable from simply pitching single vial of yeast into the original wort.  Now, that's likely enough part of my lack of understanding.  I could perhaps understand if someone let a starter develop to full attenuation, let it floc' out, and decanted the liquid prior to pitching the starter into the wort.  But why discard the (in principle overpitched) starter beer?  The only function I can guess at would be to carry off the yeast reproduction products.  I could perhaps understand if there were some semi-magical difference in yeast characteristics from growing up in a limited environment and running out of food prior to floc'ing out.  Maybe.  But to my very linear mind, I don't understand the workings of making up starters to attain a certain pitch rate.  Do understand, I say "I don't understand," and am not saying there is no difference.  It's a good day when I learn something, and I'm hoping this august group can "make my day."

Michael T.

Offline bboy9000

  • Assistant Brewer
  • ***
  • Posts: 216
  • KCMO
    • View Profile
Re: first principles question on starters
« Reply #1 on: August 03, 2013, 01:34:29 PM »
There are a few reasons to potentially make a yeast starter.  One is the amount of yeast cells in a pack or vial of liquid yeast is around 100 billion cells.  Usually this isn't enough cells to ensure a fast, healthy fermentation for five gallons of wort. Making a starter gives the yeast cells time to grow and multiply, creating more yeast cells available for pitching.  Under pitching may result in pronounced esters which add flavor or a prolonged lag time which could give other microorganisms time to grow in the wort.


Another reason for making a starter is when the liquid yeast is old, or close to the expiration date.  In this case there would be fewer viable cells in the vial or pack.  If you suspect the has been mishandled, then a starter may be a good idea, even if it has been recently packaged.

Many brewers make a starter beer for the yeast a few days or a day before brewing.  Some let the starter ferment out and others try to catch it at high krausen.  I use 1g of dried malt extract for every 10mL of liquid when making a starter wort.  This keeps the gravity between 1.030-1.040.  I mostly brew 5G of ales with moderate gravity so I usually do approximately 2L of starter 12-18 hours before I plan on pitching the yeast into the finished wort.  I pitch the entire starter unless the starter is greater than 2L or if it is a lighter beer.  In those cases I do the starter a few day ahead of time, chill it until the yeast floc out, then decant and pitch on brew day.

I use two online yeast calculators to determine the proper starter size:
http://www.mrmalty.com/calc/calc.html
http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

There are people on the forum more qualified to give you an explanation and I'm sure someone may correct some of what I have said so stay tuned.  There are definitely brewers here that will hopefully offer a more detailed scientific explanation.

« Last Edit: August 03, 2013, 01:38:51 PM by bboy9000 »
Brian
mobrewer

Offline mabrungard

  • Senior Brewmaster
  • ******
  • Posts: 1097
    • View Profile
    • Bru'n Water
Re: first principles question on starters
« Reply #2 on: August 03, 2013, 01:35:58 PM »
The primary difference is that in a starter culture, you are aiming for an aerobic environment.  That condition promotes yeast growth and formation of an adequate sterol reserve in the yeast so that they can continue to bud and reproduce well in the anaerobic (or at least far less aerobic) environment in the fermenter. 

The objective of a starter is yeast growth and in the fermenter it is alcohol production and adequate yeast longevity and vigor.
Martin B
Carmel, IN

BJCP National
Foam Blowers of Indiana (FBI)

Brewing Water Information at:
https://sites.google.com/site/brunwater/

Like Bru'n Water on Facebook for occasional discussions on brewing water and Bru'n Water

Offline bboy9000

  • Assistant Brewer
  • ***
  • Posts: 216
  • KCMO
    • View Profile
Re: first principles question on starters
« Reply #3 on: August 03, 2013, 01:41:08 PM »
The primary difference is that in a starter culture, you are aiming for an aerobic environment.

And oxidized beer tastes bad so this is why some prefer to decant the starter wort before pitching.
Brian
mobrewer

Offline denny

  • Administrator
  • I must live here
  • *****
  • Posts: 11660
  • Noti OR [1991.4, 287.6deg] AR
    • View Profile
    • Dennybrew
Re: first principles question on starters
« Reply #4 on: August 03, 2013, 02:12:14 PM »
I would like to understand the difference (and underlying reasons for any difference) between pitching a single vial of yeast into 5.5 gallons of wort vs. taking a half-gallon of that wort and making up a starter, then pitching the yeast into the remaining wort.  I do not presently understand.  I'm a physicist and would like to be further educated in matters of brewery.

From what I have read, one might view the process as fencing off 10% of the brew volume, pitching the yeast vial into it, and then at some nebulous time later (at or after high kraeusen) removing the fence.  Somehow the confinement of the yeast (the only difference I can see) results in something different from simply pitching the yeast vial into the original wort volume.

My most recent batch (#8 after a 30 yr hiatus in brewing) was also my first >5 gallon batch.  I made up 11.5 gallons of 1.044 wort for a saison-like brew.  I diverted 1.5 qts into a half-gallon glass jar, pitched the very fresh vial of WLP585 saison iii blend into it, and watched it while I gathered the rest of the wort into a 15 gallon fermentation vessel.  Very few hours later the foam on the starter had risen to about 3", very nearly overflowing the starter vessel, so I pitched the whole thing into the 11 gallons of wort.  Within a few hours, vigorous fermentation had begun (which means to me that the wort had become saturated with CO2 so that the excess was bubbling out of it).  By the morning of the second day (75F ambient temps, no chilling of the wort prior to pitch -- it was just room temp) all signs of fermentation had ceased.  The sp. gr. measured 1.006, an apparent 86% attenuation in 40-ish hours.  In the few days since then, no further attenuation has been apparent, and the beer is holding 1.006.  This mash did not exceed 150F, so I expected to have a high fermentable fraction of sugars, but that appears to be a phenomenal fermentation rate for a single vial of yeast in 11.5 gallons of wort.

The use of a starter-like process with so short a starter growth period seems to me to be indistinguishable from simply pitching single vial of yeast into the original wort.  Now, that's likely enough part of my lack of understanding.  I could perhaps understand if someone let a starter develop to full attenuation, let it floc' out, and decanted the liquid prior to pitching the starter into the wort.  But why discard the (in principle overpitched) starter beer?  The only function I can guess at would be to carry off the yeast reproduction products.  I could perhaps understand if there were some semi-magical difference in yeast characteristics from growing up in a limited environment and running out of food prior to floc'ing out.  Maybe.  But to my very linear mind, I don't understand the workings of making up starters to attain a certain pitch rate.  Do understand, I say "I don't understand," and am not saying there is no difference.  It's a good day when I learn something, and I'm hoping this august group can "make my day."

Michael T.

Michael, start by looking at this...www.mrmalty.com .  That should give you some insight into what and why.

I also think you have a misconception about the timeline.  I generally make starters 5-7 days ahead of the day I'm going to brew.  That allows for sufficient time for yeast cell growth.  Another advantage is that after the starter ferments out, you can pour off the starter wort so it doesn't go into your nice fresh wort.  My experience has proven to me that I make better beer by doing that.  Another misconception is that you use part of the wort from your batch for the starter.  As you have found, doing that doesn't provide enough time for cell growth.

Although you didn't ask, I'll also mention that 75F ambient is far too warm to make good beer, and if you don't chill the wort first (unless I misunderstood), those negative effects will be exacerbated.
« Last Edit: August 03, 2013, 02:14:27 PM by denny »
Life begins at 60.....1.060, that is!

www.dennybrew.com

The best, sharpest, funniest, weirdest and most knowledgable minds in home brewing contribute on the AHA forum. - Alewyfe

Offline dertiefster

  • 1st Kit
  • *
  • Posts: 5
    • View Profile
Re: first principles question on starters
« Reply #5 on: August 03, 2013, 02:44:34 PM »
I have been enlightened significantly from your comments.  Thank you all.  The most significant issue I'd overlooked was (apparently) oxygenation of the starter.  I see clearly that one would, after raising yeast in an oxygenated environment, choose to decant the beer and "pitch it" elsewhere than into the fresh wort.  What I did with the WLP585 was essentially proofing the yeast (as a baker might say) rather than making a yeast-multiplying starter.  I used the wort I had so I could check for yeast activity, and got that in spades.

The WLP585 I used is one of the saison yeasts, and I thought that after reading about WLP565 and temps up to (or above) 90 F, that a 75 F fermentation would not be out of line for a Belgian farmhouse temperature.  My #4 (post-hiatus) was a blonde ale much like this saison-ish attempt, and I used WLP566 in that batch [addendum: and it turned out _very_ well from my standpoint -- its dwindling supply is what moved me to do this 11 gallon batch].  Without referring to the notes, I believe I left the beer in the carboy 4 wks overall.  It took _much_ longer to finish (1.050 to 1.002?), but the rate of CO2 generation in the last 3 weeks was very low from watching the lock bubble rate -- 1-2 bubbles per minute.  I think that's still too high a rate for it all to have come from simple diffusion of the CO2 from the lower reaches of the beer.

From my perspective, this WLP585 yeast (I think it's a blend) tore through the 1.044 wort in something around 40 hours.  That's not what I'd expect from under-pitching, but I'm absolutely NOT an expert.  I'm just curious about reasons and mechanisms.  I've read speculations about pH and CO2 content, and it is possible that this batch is stalled near F.G. due to CO2 saturation or pH.  I don't have a good way to measure pH, but I _could_ shake/swirl the barrel to try to dislodge some of the CO2.  It was Thursday when I last measured the sp. gr., and I probably ought to do that again before doing a hasty bottling of the brew.  I'd not like to have a bunch of points of gravity turn into CO2 in-bottle.  Ka-boom/splash.

with many thanks...

Michael T.
« Last Edit: August 03, 2013, 02:50:07 PM by dertiefster »