[S. cerevisiae]

Being that beer is a mix of art and science, I think scientific studies can be misleading for brewers when they just focus one aspect: yeast health.  Case in point: it is better from a yeast health perspective to pitch an active starter, but from a tasty beer perspective it isn’t always the best option, because the starter wort has undesirable flavors.

There's nothing art about fermentation.  Fermentation is an area of brewing that is bounded by science.  Fermentation is little more than controlled spoilage.

One does not have to wait until fermentation is complete to settle the yeast cells and decant.  I have yet to encounter a brewing strain that will not cease to ferment and start to sediment when placed into a refrigerator set at 3C to 4C, which is what the temperature at which the average home refrigerator is set in the United States.

If you want to get testimony from a convert, ask Jim about his experience with crashing, decanting, and pitching at the end of the exponential phase.

[JT]

Being that beer is a mix of art and science, I think scientific studies can be misleading for brewers when they just focus one aspect: yeast health.  Case in point: it is better from a yeast health perspective to pitch an active starter, but from a tasty beer perspective it isn’t always the best option, because the starter wort has undesirable flavors.

There's nothing art about fermentation.  Fermentation is an area of brewing that is bounded by science.  Fermentation is little more than controlled spoilage.

One does not have to wait until fermentation is complete to settle the yeast cells and decant.  I have yet to encounter a brewing strain that will not cease to ferment and start to sediment when placed into a refrigerator set at 3C to 4C, which is what the temperature at which the average home refrigerator is set in the United States.

If you want to get testimony from a convert, ask Jim about his experience with crashing, decanting, and pitching at the end of the exponential phase.

The art referred to in my post was in regards to the taste of beer with an entire starter pitched into it. 
At any rate we appear to agree here, crash earlier rather than later.  Looks like I can crash even earlier than I thought, which is fine by me.  I made a starter Friday night with WLP002, crashed it Saturday night in the fridge, decanted and pitched it Sunday around 5pm.  When I checked on it today at 6am it already had a helluva krausen on it and I have the temp controlled at 65. 

[Wort-H.O.G.]

I just leave on stir plate 18-24 hours and then put it in fridge. Mostly because I'm not home to pull it off earlier, and just throw it in fridge when I get home. Some yeast do need longer to floc, and since I decant I give myself the appropriate time for this before brew day.


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[duboman]

This is all well above my microbiological pay grade.... My question is when comparing scale of home brew pitch and commercial pitch, how relevant is the detail in all this?

I make the appropriate starter, ferment, crash, decant and pitch with proper aeration etal... The beer is really good

[Wort-H.O.G.]

I'd imagine most commercial is using slurry, not starters? My hunch is on the small scale side, starters fermented out vs partial likely not discernible - all other things considered like healthy appropriate quantity of yeast for the particular beer, good aeration of wort, proper fermentation temps, yeast nutrient, etc.


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[S. cerevisiae]

Here's another tidbit.  I rarely decanted in the decade that I brewed before taking a hiatus from the hobby.  I started to decant religiously after I started using a stir plate because the supernatant (clear green beer) from a continuously stirred culture is just foul.  However, I since gone back to using well-shaken starters because I did not find that continuous stirring resulted in a significant improvement in performance, and I do not have to be as meticulous about decanting the supernatant with a well-shaken starter.   A well-shaken starter takes like unhopped beer instead of metabolite stew.

[duboman]

Right, but we are simply decanting and pitching the yeast, not the supernatant clear green beer.

I can't imagine that here is a discernable difference in 5-10 gallons of finished beer at home brew scale.

[69franx]

Please clarify for me: the science says to refrigerate at end of exponential phase rather than when fully fermented. Exponential phase generally over 18-24 hours after pitching into starter? Or 18-24 hours after first signs of activity in the starter? What am I looking for to know that exponential phase is over? What changes will I see?

[S. cerevisiae]

proper fermentation temps

I know that what I am about to say is going to go over like a lead balloon, but the "proper fermentation temperature" argument is way over overdone in modern home brewing.   Far too many new brewers are led to believe that they have to have a temperature-controlled fermentation chamber in order to make high-quality ales.  Anyone who is having to start 5-gallon ale fermentations in the high fifties/low sixties with extremely forgiving strains like BRY 96 (a.k.a. Balllentine "Beer," "Chico", Wy1056, WLP001, and US-05) in order to produce a clean tasting product has a house microflora or yeast management problem.  To this day, I do not start ale fermentations that low on purpose. In fact, I do not artificially attemper ale fermentations (I ferment in a below-grade unfinished basement).   What starting an ale fermentation that low does is hide yeast management and sanitation problems because it favors domesticated microflora.  If one is meticulous about yeast management, sanitation, and post-boil wort handling,  BRY 96 will produce a cleanly flavored product when started at 68F and allowed to ferment up into the low seventies.

I personally believe that all brewers, whether professional or amateur, should learn basic aseptic transfer technique.   The reason why I do so is because it has a ripple effect on how one approaches yeast management and propagation as well as brewing hygiene.

[JT]

Please clarify for me: the science says to refrigerate at end of exponential phase rather than when fully fermented. Exponential phase generally over 18-24 hours after pitching into starter? Or 18-24 hours after first signs of activity in the starter? What am I looking for to know that exponential phase is over? What changes will I see?

In my test, I transferred to a cylinder and used a hydrometer.  A 2 liter 1.040 starter was done 18 hours after pitching when run on a stir plate around 70 degrees. 
This was a throwaway batch of yeast used only for testing fermentation time to get me in the ballpark.  It is very possible that not all yeast would have the same result, but 2 liters isn't a lot of wort for the yeast to go through, so it doesn't take long. 

[S. cerevisiae]

Please clarify for me: the science says to refrigerate at end of exponential phase rather than when fully fermented. Exponential phase generally over 18-24 hours after pitching into starter? Or 18-24 hours after first signs of activity in the starter? What am I looking for to know that exponential phase is over? What changes will I see?

If we assume that a White Labs vial contains 100 billion viable cells when shipped, a relatively fresh vial contains 50 billion viable cells, the maximum cell densities for 1L and 2L starters are 200 billion cells and 400 billion cells respectively, and yeast cells bud every ninety minutes after the lag phase has been exited, then we are looking at two and three propagation periods for 1L and 2L starters under perfect conditions.  Adding one ninety minute propagation period to each count to account for cell death during propagation results in three cell division periods for a 1L starter and four cell division periods for a 2L starter.


propagation_time_for_a_1L_starter = lag_time_in_hours + (3 x 90 / 60) = lag_time_in_hours + 4.5
propagation_time_for_a_2L_starter = lag_time_in_hours + (4 x 90 / 60) = lag_time_in_hours + 6

The reason why the exponential phase (a.k.a. log phase) is called the exponential phase is because the cell count grows are a rate of 2ⁿ, where n is the number of 90 minute time periods that have elapsed since the end of the lag phase.

With that said, let's calculate how long it takes 200 billion cells to reach maximum cell density in a 5-gallon batch of wort.  Five gallons is roughly 19 liters (19,000 milliliters); hence, the cell count from a 200 billion cell 1L starter has to increase by a factor of 19.  Now, we are dealing with exponential, not linear growth; hence, the number of 90 minute time periods that are required to increase the cell count 19 fold is equal to log₂(19), where log₂ is the log base 2 function.  Most calculators do not support log₂, but we can take the log₂ of n by taking the log(n) over the log(2) (i.e., log(n)/log(2)); hence, log(19) / log(2) = 5 (rounded).   Five ninety minute replication periods after the lag phase has been exited should be enough time to reach maximum cell density.

Now, anyone who is following this thread closely has probably figured out that the phase over which we have the most control in a fermentation is the time spent in the lag phase.  By stepping a culture at the end of the exponential phase, we are pitching yeast cells that require very little in the way of replenishment. Hence, we will experience a shorter lag phase than we will if we pitch a culture that has reached quiescence because a quiescent culture has to undo the morphological changes it underwent in preparation for hard times.  A quiescent culture also has to replenish the ergosterol and UFA reserves that were spent post-exponential phase, which increases dissolved O2 requirements.

Here's another thing to think about when propagating a culture.  Bacteria cells divide every thirty minutes on average.  Hence, the bacteria cell count grows by a factor of 8 every time the yeast cell count grows by a factor of 2.  Add in the possibility of a shorter lag phase for house bacteria, and it should be painfully obvious why pitching at the end of the exponential phase is preferred to waiting until the culture has entered quiescence.

[Wort-H.O.G.]

[/quote]
propagation_time_for_a_1L_starter = lag_time_in_hours + (3 x 90 / 60) = lag_time_in_hours + 4.5
propagation_time_for_a_2L_starter = lag_time_in_hours + (4 x 90 / 60) = lag_time_in_hours + 6
[/quote]

so a 4L starter = lag_time_in_hours + 12? so roughly 24hrs from pitch yeast in starter to cold crash is what you would do?

[klickitat jim]

Regarding "ask Jim", First off, its an akward honor that my brewing would be referenced as any kind of benchmark. What I did a while back is put his method to the test. I oxygenated my starter wort, pitch a smack pack, and put it on the stirplate the day before brewing. At 18 hrs (which was moring of brew day) I moved it to the fridge. Its difficult to tell for sure on a stir plare but it looked to be at high krausen at that time. Once I was done brewing and had my wort chilled I decanted and pitched. At that point the starter had about 75% settled out, there was a pile of creamy yeast at the bottom and about a 2" layer of less floculant yeast in the column above it. I decanted all but about an inch of liquid, swirled that up and pitched. By the way, that starter smelled like lovely fresh bread rather than disgusting spent starter wort. That beer took off like a storm and made a really nice beer ahead of normal schedule.

From that I learned
1. Stir plates dont do much in the way of aeration. I used to not oxygenate my starters, I do now
2. The starter is to make healthy young recruits not battle weary vetrans.
3. The reason to decant is to keep nasty spent wort out of your beer, if you crash at high krausen there's less worry about that. Some folks pitch the whole shebang at high krausen, right?

My pitching method is
1. With a new smack pack, I make a starter the day before and crash it at 18hrs
2. If I'm stepping (like for my current Helles) I crash step 1 at 18hrs and step 2 at 18hrs.
3. If im repitching and I rebrew the day after racking the first beer I do a direct measure and repitch
4. if im rebrewing more than a day later I follow the same process as if it were a smack pack.

Im not claiming this is THE way to do things, its just my way.

[S. cerevisiae]

so a 4L starter = lag_time_in_hours + 12? so roughly 24hrs from pitch yeast in starter to cold crash is what you would do?

No, you are treating cell growth as a linear process.  The cell count grows exponentially because each cell buds (divides) into two cells every growth period; hence, one additional growth period is required every time we double volume.

propagation_time_for_a_1L_starter = lag_time_in_hours + (3 x 90 / 60) = lag_time_in_hours + 4.5
propagation_time_for_a_2L_starter = lag_time_in_hours + (4 x 90 / 60) = lag_time_in_hours + 6
propagation_time_for_a_4L_starter = lag_time_in_hours + (5 x 90 / 60) = lag_time_in_hours + 7.5
propagation_time_for_an_8L_starter = lag_time_in_hours + (6 x 90 / 60) = lag_time_in_hours + 9
...


I suggested 12 to 18 hours in order to allow for sub-optimal growth conditions and starting yeast health.  The culture will often be ready to crash before 12 hours have elapsed when pitching a White Labs vial.  A White Labs vial contains an huge number of cells for the size of the medium into which it is being pitched when making a starter.

[Wort-H.O.G.]

so a 4L starter = lag_time_in_hours + 12? so roughly 24hrs from pitch yeast in starter to cold crash is what you would do?

No, you are treating cell growth as a linear process.  The cell count grows exponentially because each cell buds (divides) into two cells every growth period; hence, one additional growth period is required every time we double volume.

propagation_time_for_a_1L_starter = lag_time_in_hours + (3 x 90 / 60) = lag_time_in_hours + 4.5
propagation_time_for_a_2L_starter = lag_time_in_hours + (4 x 90 / 60) = lag_time_in_hours + 6
propagation_time_for_a_4L_starter = lag_time_in_hours + (5 x 90 / 60) = lag_time_in_hours + 7.5
propagation_time_for_an_8L_starter = lag_time_in_hours + (6 x 90 / 60) = lag_time_in_hours + 9
...


I suggested 12 to 18 hours in order to allow for sub-optimal growth conditions and starting yeast health.  The culture will often be ready to crash before 12 hours have elapsed when pitching a White Labs vial.  A White Labs vial contains an huge number of cells for the size of the medium into which it is being pitched when making a starter.

ok got it. so for what you describe, if I pitch one vial of white labs in to 4L of wort, cold crash it at about 12hrs, and then compare the slurry of that starter to 4L of wort with one vial of white labs after 24hrs on stir plate before cold crash, the slurry volume and yeast count (i have no equipment to determine this) should be the same?