Yeast growth phase, temperature and ester production

As I understood it, esters are by-products of yeast reproduction. What if I pitched a large starter at high krausen, reducing lag phase and thus reducing the rate of yeast reproduction? Do I still need to worry about esters produced by fermentation temperature that's several degrees higher than prescribed?

I'm using US-05 and my fermentation went up to 77F at one point during the first 72 hours.

No. It's still gonna have more off flavors.

An ester is produced when one organic acid and one alcohol combine together by some enzymatic activities thus at first alcohols must be created by yeast cells and enough active acids be present and also certain enzymes are be active, to finally some esters be produced.

High pitch rate =>lower yeast growth => higher acetyl-CoA => higher esters production
Low pitch rate =>higher yeast growth => lower acetyl-CoA => lower esters production
High temperature => higher fusel alcohols production + higher activity of certain enzymes => higher esters production
Higher aeration levels => higher sterols production => lower acetyl-CoA => lower esters production

Temperature plays important roles,even the most important roles in fermentation process and so in the character of beer.Its effects are not limited to one or two Cases and It affects the entire processes of Brewing.

HaDaL said:

An ester is produced when one organic acid and one alcohol combine together by some enzymatic activities thus at first alcohols must be created by yeast cells and enough active acids be present and also certain enzymes are be active, to finally some esters be produced.

High pitch rate =>lower yeast growth => higher acetyl-CoA => higher esters production
Low pitch rate =>higher yeast growth => lower acetyl-CoA => lower esters production
High temperature => higher fusel alcohols production + higher activity of certain enzymes => higher esters production
Higher aeration levels => higher sterols production => lower acetyl-CoA => lower esters production

Temperature plays important roles,even the most important roles in fermentation process and so in the character of beer.Its effects are not limited to one or two Cases and It affects the entire processes of Brewing.

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Just when I thought I had this ester thing figured out you through this pitching rate thing out! Well, I haven't really figured out the science behind ester production but the process related to brewing Belgian Pale Strongs. Ester production must be very complex and I know it is a biochemical process that I do not understand. However, if I pitch on the lower end of the recommended rate i.e. 750,000 cells/ml/degree P into 62 degree F wort and let the temp rise to 74 F over the course of the fermentation, I get the ester profile I am looking for. If I pitch at a higher rate (1.5 million cells/ml/degree Plato) with the same temps the results are less esters. While fermenting at higher temps with at either pitch rate results in ester overload.

So when I saw this, my first response was to call BS. But first I did a little research and for sure it's out there and from more than one reliable source. On the other hand, plenty of reliable sources say the opposite. Could it be strain related? I would like to hear more about ester production experiences from others out there who brew different types of beer. Those types that benefit from "clean" profiles as well as estery profiles and what works for you.

There is a difference between the flavors of esters and that of phenol. People usually think Belgians when they think of ester profiles, but I wonder if that isn't more phenolic that makes the yeast flavor so pronounced in that style.

Brewing a beer without yeast flavor to me is like brewing a beer without hop flavor, or brewing a beer without malt flavor. I personally can't stand belgians for the most part, but love yeast flavor that I would attribute to "esters". Of course every strain is different in the type and amounts of esters produced.

I think that's backwards, lower pitch = higher ester production. This is more a recalling from memory of forum posts but I think I agree with it from experience. The rest of it sounds right. Another part of me wants to redact all of this because it all seems to be theory to some extent.

I would not think pitch rate could eliminate the problems of high fermentation temp for one second. If temp is 77 not sure with something like Chico how bad but the end result is that the yeast work too fast and produce bad things. There are so many variables and theory that experience is the best thing to look to, which I don't have much in comparison to others. I will still post my mind and do appreciate when others do the same.

Yes! this Subject is very complex and still it has been remained unknown to some extent.As I know Several practical research works(not just theoretical) have been done on the subject of effects of pitching rate as well as other factors on esters production and some contradictory results have been reported by researchers.In my previous comment I tried to point it out to thread Starter that temperature is much more important than pitching rate in this subject.When some of You guys are saying " increasing pitching rate=lower esters production" ,in my opinion this is not wrong statement ever as well as if someone tells contrary.Because both of these statements may be proved in the different situations/conditions.I think the problem cause this paradox is the researchers approaches.They have been studying the factors affecting the production of esters individually and readers of their papers have selected some of the results and have reported them in the brewing literatures While these factors are present in beer all together and interact with each other in the same time.In practice We can not be sure which one has more or less impact than others on esters production based on the individual researcher's results since the several factors with opposite effects on the subject are acting there. I've not seen anywhere yet one has done the comparative study about the effectiveness of various factors. For instance assume a situation in which the factors like high temp+high gravity wort+low pitching rate+low aeration+high lipid content+high pressure+high zink content, be present at same time! In such situation will esters production be normal or lower/higher than normal?! What is normal !!?Which one of these factors is a better choice with less side effects for controlling the levels of Esters In beer with specific yeast strain? Moreover, this story becomes much more complicated when we know Esters belong to just one group of several groups of fermenting compounds which have their impact on beer flavour and aroma and also these other groups of compounds (such as alcohols,carbonyl compounds,sulfur compounds,phenols etc.) are present in beer and act/react/interact together and with other compounds ( such as malt and hops compounds,other micro-organisms products) that affect character of beer at the same time of esters .Personally, I'm not able to drink a beer and exactly find out if the extent of the more than 800 components that make up the flavour of beer is been too much or too little.However, I think what is important for us is the final flavour and aroma of beer which is the results of so many things including esters and obviously the normality depends on everyone's taste besides the styles guidelines.I would try to brew the beers that I like constantly via experimenting and recording the experiences.as pros have said It seems nothing is better than experience.
Sorry, this comment was became a little long, and thank you for suffering my horrible English!

Most homebrewers don't seem to get to the point of caring. They think a yeast flavor is only at its best when given optimal growth conditions. By the time they invest in pure 02 systems they have too much riding on it to consider going back to under-aeration.

Most megabreweries just struggle with consistency and would never mess with anything less than ideal yeast health.

Most science geeks with access to equipment and free time to experiment on such things are either very young and inexperienced homebrewers, or employed by a major brewery who would probably not have much interest in sharing its results for optimal ester production.



So that leaves experimentation on your own. So far I've only messed with no aeration, over aeration, zinc additions, lipids, under-pitching and over-pitching.

So far my favorite is a mega underpitch of highly viable yeast with very limited oxygen in a colder-side of things ferment of 1.070ish wort with limited trub.

I'd like to mess around with FAN a little in the future as well as pressurized fermenting to see those affects on yeast flavor.

grathan said:

So far my favorite is a mega underpitch of highly viable yeast with very limited oxygen in a colder-side of things ferment of 1.070ish wort with limited trub.

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Thanks! Could you say more about;

Mega underpitch: Please quantify, estimated cells per ml in your 1.070ish wort or some other measurement?

Highly viable yeast: How are you producing this?

Very limited oxygen: I'm guessing you are highly aerating your starter. What are you doing to the wort?

Sure I can try.

Are you familiar with a thimble? I use about half a thimble full of viable yeast. I would guess that is 2ml of slurry? It's viable because it just came from a growth within 5 days (the growth was a stirred starter with zinc added).

No 02. I run the wort from a spigot into a carboy. There is some foaming, but it is not intentional. In fact it's probably just star san.

grathan said:

Sure I can try.

Are you familiar with a thimble? I use about half a thimble full of viable yeast. I would guess that is 2ml of slurry? It's viable because it just came from a growth within 5 days (the growth was a stirred starter with zinc added).

No 02. I run the wort from a spigot into a carboy. There is some foaming, but it is not intentional. In fact it's probably just star san.

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WOW! Being generous with the numbers, that works out to approximately 7500 cells per ml in your finished batch, assuming you are doing a 5 gallon batch. I've worked my way down to 8,500,000 cells per ml for my similar gravity worts.

BTW, I remember thimbles and my Mom referring to a thimble full when talking about small quantities.

So call me daddy?

trentm said:

WOW! Being generous with the numbers, that works out to approximately 7500 cells per ml in your finished batch, assuming you are doing a 5 gallon batch. I've worked my way down to 8,500,000 cells per ml for my similar gravity worts.

BTW, I remember thimbles and my Mom referring to a thimble full when talking about small quantities.

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Edit: That would actually be 126,300 cells per ml in the finished wort. I had originally calculated cell per ml per degree Plato. Still, that is a mega underpitch!

This topic is very complex and very much the focus of my brewing lately.

I have come to the realization that one needs to have a strategy for a desired flavor outcome that includes yeast amount, oxygenation and fermentation temps together. Sadly, as stated, this involves a lot of experimentation and risking less than optimal batches.

Also, the separation of esters and phenols can be confusing. I like Bavarian Hefeweizen. Would you consider this style phenolic or Estery? I would call it phenolic. So how do you get more phenols?

Sounds like a great topic for a Basic Brewing experiment.

trentm said:

Edit: That would actually be 126,300 cells per ml in the finished wort. I had originally calculated cell per ml per degree Plato. Still, that is a mega underpitch!

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Don't forget this yeast will be able to bud a couple times and the original cells will consume wort even into highly alcoholic state. So while the stressed offspring spew esters into the beer, the orginal cells (with strong cell walls) ferment to final desired attenuation, at least that is what I am thinking.

At the very least your not losing precious wort to aerobic fermentation.

HaDaL said:

An ester is produced when one organic acid and one alcohol combine together by some enzymatic activities thus at first alcohols must be created by yeast cells and enough active acids be present and also certain enzymes are be active, to finally some esters be produced.

High pitch rate =>lower yeast growth => higher acetyl-CoA => higher esters production
Low pitch rate =>higher yeast growth => lower acetyl-CoA => lower esters production
High temperature => higher fusel alcohols production + higher activity of certain enzymes => higher esters production
Higher aeration levels => higher sterols production => lower acetyl-CoA => lower esters production

Temperature plays important roles,even the most important roles in fermentation process and so in the character of beer.Its effects are not limited to one or two Cases and It affects the entire processes of Brewing.

Click to expand...

In addition to these relationships, wort gravity impacts ester production. Going from 10P to 20P increases the ester level at least fourfold. This is why high gravity beers have very estery character. The prime players are Acety-CoA, alcohols, and alcohol acetyl transferase (a strain dependent enzyme).

Pressure is pretty big as well. Tall fermenters push down on the yeast cake and supress esters.



One thing it seems to be aware of with underpitching, is the presence of diacetyl in the finsihed beer. Geoge Fix makes reference to a study by Hoffman? but I can't find anything on that.