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From what I read in most publications, ester production tends to increase at lower pitching rates. It's not a linear relationship by any stretch of the imagination; in fact there seems to be some sort of a U-curve at work here but, generally and broadly speaking, a lower pitching rate (even to the point of judicious underpitching) tends to produce higher levels of fruity esters, while overpitching tends to lead to a "cleaner" flavour profile with lower levels of fruity esters.

(Of course the pitching rate is only one factor here; the yeast's genetic make-up, wort composition and fermentation temperature all play large roles in ester production as well. But let's treat these as constants for now.)

The rationale behind a higher ester production at lower pitching rates appears to be that the enzymes that produce these esters during fermentation (not during the yeast growth phase as some home brewers mistakenly believe) are located in the yeast's cell walls, and that more yeast growth leads to more cell wall biomass and therefore more esterification enzymes.

My question: what is the difference between cells resulting from more growth as a result of a low pitching rate, and cells that have been pitched at a high pitching rate, in terms of ester production?

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The cells are generally not different, it's how they behave is what is significantly different. Yeast have phases they follow when conditions are met they move on.

Yeast like all organisms only want to reproduce. This is all they do. Prepare for and reproduce until they can't due to conditions. Then lay in wait until they can reproduce again.

Some basics: Yeast reproduce by cell division budding. 1 Cell becomes 2 but the mother cell remains the same size feeding and growing the daughter until it releases. Sugar is the metabolic fuel the Cell needs to do this. Cell size, solution enviroment and colony size appears to be the division triggers. These new cells then take in chemicals and expel waste (eat and shit) to grow in size until they are ready to divide. The mother cell also continues to feed and may be ready to divide again before it's last daughter will.

New and old cell differences. Bud Scars. When a cell divides a scar is formed at the separation point. These scars on the cell wall don't appear to have pathways like the rest of the healthy wall. So the more times a cell has divided the less viable surface area the cell wall has to take in chemicals. So they will do less work for a brewer compared to a new cell.

*3 phases Lag, Exponential Growth, Stationary Growth.

These phases need to be viewed as a whole colony average. As each individual cell is just doing what it can to reproduce based on its environment, and not all cells are in the same state of reproduction. As the environment changes we see these phases manifest.

Row, Row, Row your boat RRRYB https://en.m.wikipedia.org/wiki/Round_(music) This is a terrible analogy and may not translate well to other culters, but RRRYB is sung by a crowd with different groups starting at different times to make a perpetual canon but then sync up in catches.... Picture a colony of yeast as RRRYB but there's a finite amount of words (nutrients,o2, sugars etc) each new cell starts to sing at different times. These "catches" are the phases we see. Songs over once out of "words"

colony density flocullation is when cells stick together due to electrical charges. When a cell has a few other cells stuck to it, it's speculated that this triggers a life cycle phase for the cell to go dormant. Much like locus only swarm when the colony gets too big or dense, the the trigger is repeated contact from other locus. Its survival trigger, food will run out quickly so move on. With yeast they can't move on, so they wait, until they have oxygen or sugar again. Production of co2 helps physically separate cells giving the cell buoyancy, when sugar is limited co2 isn't produced and flocculation isn't defeated anymore.

Esters When a cell is budding without enough oxygen, is when esters are produced. New cells birthed in a deprived environment are weaker, these cells have been observed at producing more esters than healthy cells as they bud thier daughters.

Answer The difference in colony is how many cells you have of a specific age. Older cells having stronger cell walls but more bud scars.

Ester control is all about how much yeast, oxygen, nutrients, sugar there is. Manipulate esters by controling the oxygen free window of time before flocculation.

  • "When a cell is budding without enough oxygen, is when esters are produced.". Perhaps this could be the cause of the commonly held misconception that underpitching increases ester production? Underpitching promotes growth, which starts as aerobic growth (aerobic metabolic pathways are preferred over anaerobic ones) which consumes oxygen, thus forcing the yeast into budding without oxygen and producing esters. If underpitched beers are also under-oxygenated (which seems a plausible scenario) this could create the impression that underpitching results in estery beers. What do you think? – Frank van Wensveen Jun 8 '18 at 12:01
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To complicate things even more... There is also evidence that heavy "over pitching" of yeast will produce similar higher esters to heavy "under pitching". The rational seems to be that fermentation finishes with less reproduction and a lower number of yeast generations. These earlier generations create more esters due to reduced energy toward reproduction, and are born into a higher sugar environment so they tend to flocculate in mass post fermentation rather than stay in suspension and clean up some remaining esters.

Plenty of disagreement out there over whether over pitching causes a beer to be cleaner or have more esters. My guess is that it is somewhat strain dependent.

  • Strain dependent, and also dependent on oxygenation and wort gravity. Higher ester formation at higher pitching rates seems (!) mostly the province of industrial lager brewing (using Pastorianus, high gravity brewing and higher levels of oxygenation) than is the case in home brewing and most craft brewing (using Saccaromyces, standard gravities and lower levels of oxygenation). Both higher and lower ester levels at higher pitching rates are cited in literature and have been observed in practice, so both schools of thought are probably right, depending on circumstances. – Frank van Wensveen Jul 13 '18 at 7:59

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