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Messages - Saccharomyces

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1
Classifieds / Schmidling Model P Malt Mill
« on: August 11, 2018, 11:25:38 PM »
If anyone who lives in Central Maryland is looking for a mill to crush grain, I have a Schmidling Model P Malt Mill that I would like to sell for $60.00.

2
Yeast and Fermentation / Re: Optimizing yeast starters.
« on: August 03, 2018, 12:13:52 AM »
Your process may save money, but it produces cultures with low ergosterol and unsaturated fatty acid reserves.   There is reason why cultures and batches are pitched and stepped at high krausen.  Your process also results in low O2 content.

3
Yeast and Fermentation / Re: Vindication for us non-rehydrators
« on: July 29, 2018, 12:44:45 PM »
Interestingly, their technical data sheet suggests an alternate method:  sprinkle on top of wort in the fermenter, leave 30 minutes, then aerate to mix.  Maybe I'll add the aeration step.  Or not.

In reality, unless one is seriously underpitching, wort does not need to be aerated when using dry yeast.  Dry yeast is grown under aerobic conditions below the Crabtree threshold in a bioreactor.  It is a very efficient way to propagate yeast cells because yeast cells produce more energy from the medium using the aerobic metabolic pathway instead of the anaerobic metabolic pathway.  The bonus is that the cells come out of the bioreactor with fully charged ergosterol and unsaturated fatty acids reserves.  The reason why we aerate wort is to provide O2 for the synthesization of these compounds during the lag phase.

4
Yeast and Fermentation / Re: Another stir/no stir question
« on: July 29, 2018, 12:28:39 PM »
I pitched more harvested slurry than fresh yeast.  I maintained most of the cultures I used for brewing on agar slants, so a new culture was a several day event that started with 20 to 40ml of 5% w/v (1.020) wort that had been pressure cooked.  Many of the cultures I used are not available via the homebrew trade.

5
Yeast and Fermentation / Re: Another stir/no stir question
« on: July 28, 2018, 01:11:47 PM »
I have never run side-by-side tests with O2.   What I did to disperse the cells in a batch is to cap the carboy, place it on its side, and roll it back and forth.

6
Yeast and Fermentation / Re: Trub resting on top of yeast
« on: July 28, 2018, 01:02:40 PM »
Here's one of the reasons why one should never rinse yeast with water.  It is an unnecessary step that opens the culture up to infection because it raises the pH of the culture.  Cropped yeast is best stored under beer.  Yeast rinsing buys one absolutely nothing in the grand scheme of things.  It is like using stir plate for making starters.  Stir plates were designed to stir things, not grow cultures.  The proper mechanical device for growing cultures is known as a shaker table.  The correct flask to use on a shaker table is a shaker flask.

Anyway, to answer the OP's question.  I would pitch the culture into starter medium, wait a few hours to allow the cells to go into suspension, and then decant the liquid fraction to another sanitized vessel if you desire to separate the yeast cells from the trub.  That being said, a little trub never hurt a culture.  That is why there is zero reason to rinse yeast.

7
Yeast and Fermentation / Re: Another stir/no stir question
« on: July 28, 2018, 12:52:43 PM »
I used to shake after pitching the culture.  The culture was pitched and then shaken to disperse the cells and aerate the starter medium.  Turning the starter medium into almost all foam was the result of being a much stronger younger man.  I eventually started to shake and then pitch to minimize stress.

When aerating wort with O2, I personally would aerate before pitching.  The wort is ready to go when the culture is pitched.

8
Yeast and Fermentation / Re: Back from a close call
« on: July 28, 2018, 12:43:20 PM »
There was a session in Portland you will love when it gets posted on the AHA site. A Prof at U of WA tracked genetic changes through sreial repitches at Post Doc Brewing  (Dr. Tom Schmidlen used to be on here before he went pro). I think you will enjoy it, as it was one of the Chico strains IIRC.

What is interesting about a diploid brewing strain is that it is more prone to genetic drift due to having only two sets of chromosomes.  The polyploids are more drift resistant because they can have more than one copy of a beneficial allele.  The fact that so many of the brewing strains are polyploids has to be due to serial repitching.  Serial repitching is an example of selective pressure on an organism. 

9
Yeast and Fermentation / Re: Back from a close call
« on: July 28, 2018, 12:43:48 AM »
I saw the yeast genome project post, and there are a lot of questions in my mind.  I previously posted a link to the Dunn and Sherlock publication in which the Ballantine culture BRY-96 (a.k.a. Chico) was shown to be a diploid yeast strain having many of the genetic markers of the saccharomyces cerevisiae parent of saccharomyces pastorianus (https://genome.cshlp.org/content/early/2008/09/11/gr.076075.108.full.pdf).  Diploid brewing strains are unique because most brewing strains are polyploids with three (triploid) or four (tetraploid) sets of chromosomes.  The beauty of a diploid strain is that it can undergo sexual reproduction (meiosis) in addition to asexual reproduction (mitosis).  Brewing cultures are produced via mitosis. New yeast strains are produced via meiosis.

10
Yeast and Fermentation / Re: Another stir/no stir question
« on: July 28, 2018, 12:29:16 AM »
Here is the thing. One is not going to exceed maximum cell density for a given volume.  The average White Labs culture has around 100B cells.  Maximum cell density for a 1L starter is approximately 200B cells.   Even if the culture is 50% viable, one is looking at two replication periods to reach maximum cell density.  That is around 180 minutes beyond the lag phase.  If one is pitching a 50% viable White Labs culture into 2L of starter medium, that only extends propagation time by 90 minutes.  Most White Labs 1L  and 2L cultures are ready to pitch in 12 hours or less.  A stir plate buys you nothing.  All it does expose the cells to shear stress.

11
I do not believe that it is a fermentation issue. What are the OP's mash temperatures. One is not going to obtain those attentuation levels without a highly fermentable wort.   The OP should try a single temp mash at 65C/149F for an hour to ninety minutes and report his results.

1 - (11 / 62) = 82% AA
1 - (13 / 66) = 80% AA


1 - (16 / 61 ) * 100 = 74%
1 - (19 / 65) * 100  = 71%


12
Yeast and Fermentation / Re: Yeast Cell Count, Diameter, and BioMass
« on: July 27, 2018, 10:23:44 AM »
FWIW I increase the volume by about 1/3 to 1/2 for lager yeast if I'm pitching around 50°F.  Seems to work right.  I would think that lager yeast is just yeast, and if pitched at say 60°F, it would not need an increase, but would grow sufficiently.  Would be nice to hear from the expert.

Pitching a larger culture with a lager fementation reduces the time to high krausen because yeast cells replicate slower at lower temperatures due to reduced metabolic rate.   The beauty of lager fermentation and why it made industrial brewing possible is because lager yeast can function at lower temperatures than bacteria and other spoilage microflora that are often found in breweries.

13
Yeast and Fermentation / Re: Yeast Cell Count, Diameter, and BioMass
« on: July 27, 2018, 10:16:51 AM »
Lager yeast cells also tend to be smaller than ale yeast cells.  That is why I have always prefaced maximum cell density with the word "approximately." Maximum cell density is based on the space between cells while the culture is in suspension, not count.  A smaller cell size results in a higher cell count before maximum cell density is reached.

Amateur brewers get far too wrapped around the axle when it comes to yeast cell counts.  Yeast cultures are truly like nuclear weapons in that close with healthy cells (i.e., cells with good plasma membrane health) is more than good enough because a culture grows exponentially until maximum cells density is reached or the medium is spent.

The reason why high gravity beer requires a larger biomass is because it is more difficult to dissolve O2 in high gravity wort and osmotic pressure is high.  Osmotic pressure occurs when the solution on the outside of the cells has a higher solute (what is dissolved in the solution) level than the fluid inside of the cells.  Water is drawn to the side of the plasma membrane with the higher solute level, which is the wort.  The migration of fluid from inside of the cell to the wort causes the cells to shrink and the cell membrane to lose turgor pressure (turgor pressure holds the cell membrane up against the cell wall), which can result in cell implosion.   That is why it is a good practice to pitch at high krausen instead of waiting for a culture to ferment out.  Pitching at high krausen yields the maximum viable biomass while ensuring that the cells still have strong and pliable plasma membranes due to having good ergosterol and unsaturated fatty acid reserves (UFA).  Waiting until the cells have reached quiescence (fermented out) before pitching results in a brewer pitching cells that have lower ergosterol and UFA reserves; thus, weaker and less pliable cell membranes.  That is why I tell people to ditch the stir plate until quiescence is reached approach that has become fashionable in the last decade or so.  A stir plate does not buy a brewer much when growing yeast biomass because brewing cultures tend to stay in suspension until the sugars that a culture can break down to glucose becomes limiting. What is important is dissolved O2 when the culture is pitched because O2 is used synthesize ergosterol and UFAs during the lag phase.  Anyone who has used pure O2 or the poor man's O2 bottle (a.k.a. SNS) to aerate the medium before pitching understands this fundamental.

14
Yeast and Fermentation / Back from a close call
« on: July 27, 2018, 12:26:47 AM »
I just wanted to let those who know me know that I have been away for a good reason.  I suffered a silent heart attack in August of 2016 and had to undergo coronary artery bypass graft surgery in September of 2016.  Three grafts where performed on my heart (a.k.a. a triple bypass).  I have adopted a much healthier lifestyle, which includes beer, but more red wine. I have also lost 40lbs.  I have missed contributing to the AHA forum, and I miss my blog. Denny contacted me not long ago about his and Drew's forthcoming book, and it made me think about all of the people who make this forum great.

15
Yeast and Fermentation / Re: Dregs/stir plate
« on: July 27, 2018, 12:15:20 AM »
AFAIK, Crabtree is only about the presence of glucose, not whether it's aerobic.

The Crabtree effect is based on percentage of glucose in the medium.  Below the Crabtree threshold and in the presence of O2, reproduction is respirative. Above the Crabtree threshold, all reproduction is fermentative, regardless of O2 level.  The difference is lies ergosterol and unsaturated fatty acid (UFA) reserves when maximum cell density is reached as well as the usage of adenosine triphosphate (ATP).  Cells produced under the Crabtree threshold in the presence of O2 have fully-charged ergosterol and UFA reserves.  Cells produced above the Crabtree threshold share the ergosterol reserves of their mother cells; therefore, a mother cell shares a portion of its ergosterol and UFA reserves every time it buds a daughter cell.  Dry yeast is produced using a continuous process that holds the medium in a steady state below the Crabtree threshold, which means that dry yeast cells have fully-charged ergosterol and UFA reserves.  That is why dry yeast can be pitched into poorly aerated wort.

As I have mentioned many times, a stir plate does not oxygenate wort after it is offgasing. All it does is keep cells in suspension.  One should be pitching or stepping a culture at high krausen, which means that a stir plate does not buy one much when propagating yeast cells.

When propagating a culture from dregs, one should start with about 25 to 50mls of 1.020 wort.  That culture can be stepped by a factor of 10, but a factor of 4 to 5 is more foolproof (50 -> 250ml -> 1L).  The culture should be stepped as soon as it reaches high krausen.  High krausen signals the transition from exponential growth to the stationary phase where reproduction is for replacement only.  I cover this area of yeast management in the following blog entry: https://www.experimentalbrew.com/blogs/saccharomyces/yeast-cultures-are-nuclear-weapons



Saccharomyces (a.k.a. S. cerevisiae)

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