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Cell membranes and temperature fluctuations

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Delaney

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Hi there,

so I'm a university student, and I'm currently studying cell biology. I'm learning about how temperature affects the fluidity of the cell membranes, and the metabolic responses than ensue to maintain the membrane's physical state.

Is this the reason why we don't want temperatures to fluctuate during fermentation?

If so, how does the metabolic response of these yeast cells to changes in temperature negatively effect (a) yeast health, (b)fermentation, or (c)the chemical composition of the beverage in question?

Thanks for the insight,

Delaney.


Update
well, for those that are curious, I happened upon a professor of cellular biology today, to whom I posed this question. His reply: "absolutely".

For those less familiar with cell membranes, they are composed primarily of molecules called phospholipids. Phospholipids have two fatty acyl chains each, which can either be saturated or unsaturated. unsaturated fatty acyl chains increase the membrane's fluidity, and saturated fatty acyl chains increase the rigidity of the membrane. In order to carry out necessary biological functions, a cell membrane must maintain a relatively constant fluidity. If a given membrane were to remain unchanged, and the temperature were lowered, it would lose it's fluidity and become gel-like, inhibiting it from functioning properly.

When exposed to temperature fluctuations, the cell membrane responds metabolically by interchanging saturated/unsaturated fatty acyl chains in it's membrane. By either increasing/decreasing membrane fluidity, the cell can resist to changes in temperature. In the context of brewing, this metabolic response is what negatively affects life cycles of yeast/bacteria cells, as they are forced to focus on the homeostasis of cell membrane fluidity.


And that is why temperature fluctuations during fermentation is bad. I'm still curious as to the changes in chemical composition which occur as a result of the homeostasis of membrane fluidity in yeast cells.



UPDATE
Today I had the chance to speak with Dr.George van der Merwe, a specialist in the microbiology of saccharomyces, providing valuable insight which I'd like to share with the HBT community.

As previously stated, cell membrane fluidity is vital for the biological functions of yeast/bacteria. Embedded or attached to the cell membrane are proteins which carry out various functions, such as transporting nutrients into the cell. If cell membrane fluidity is compromised due to heat/cold stress, the functionality of these proteins will be negatively impacted.

According to Dr.Merwe, heat stress is to be avoided as this will cause metabolism to reach levels too high, resulting in excessive biomass production. Furthermore, these higher temperatures will encourage the evaporation of volatile compounds, resulting in a "flat" tasting wine/beer, an indicator of an amateur product. Dr.Merwe indicated that a slower fermentation at the cooler end of a yeast's temperature range will produce a higher quality wine. He indicated that if fermentation is sluggish, the temperature could then be raised slightly to kick off fermentation. The implication is that a slower fermentation at cooler temperatures is better than a quick fermentation at slightly higher temperatures.

That being said, temperature fluctuations within the yeast's acceptable temperature range will not produce ill-effects. It is only when temperatures fluctuate outside of the yeast's range that cold/heat stress will occur, negatively impacting yeast metabolism and overall quality of the beverage in question.





I was curious as to where fatty acyl chains could be acquired/sent by phospholipid molecules in order to adapt to changes in temperature. During metabolic response to temperature fluctuations in saccharomyces, fatty acyl chains of phospholipids are not released into the "broth". Rather, the fatty acyl chains are sent/acquired intracellularly (within the yeast cell) in vacuoles, where they are stored.

Another option is that fatty acyl chains can be interchanged between phospholipids of the cell membrane itself. This is effective because a phospholipid with two unsaturated fatty acyl chains is much more (disproportionaly) resistant to cold temperatures than a fatty acyl chain with only one unsaturated chain. Example 2 is therefore considerably better suited to deal with cold temperatures than Example 1:

Example 1:
phospholipid A:
-1 saturated fatty acyl chain
-1 unsaturated fatty acyl chain
phospholipid B:
-1 saturated fatty acyl chain
-1 unsaturated fatty acyl chain

Example 2:
phospholipid A:
-1 unsaturated fatty acyl chain
-1 unsaturated fatty acyl chain
phospholpid B:
-1 saturated fatty acyl chain
-1 saturated fatty acyl chain


The inverse is true as well. Hotter temperatures render the cell membrane more fluid, therefore the phospholipids will acquire more saturated fatty acyl chains to deal with this stress.







I am currently brewing lambic beers, so I asked whether these concepts apply to lactobacillus/brettanomyces. He told me that these organisms are not well understood on a microbiological level, and it is therefore a guessing game as to their sensitivy to temperature fluctuations or what not. Furthermore, bacteria are known to release vacuoles containing phospholipids/fatty acyl chains outside of the cell. These compounds may then react with other molecules in the "broth", which will likely result in aromatic/flavour compounds being formed. It is therefore more than likely that this occurs with bacteria such as lactobacillus.


Finally, I found it interesting that these phospholipids, fatty acyl chains, other proteins of the cell membrane are released by saccharomyces when autolysis occurs. Normally, this is to be avoided. Interestingly, these compounds aid in bubble formation with respect to sparkling wines, therefore a certain amount of autolysis is desireable in this circumstance, to a limited extent. A greater percentage of lees would result in more of these compounds being released/formed, producing a yeastier tasting wine. Using less lees would result in a fruitier tasting wine.

Because vacuoles containing these compounds are likely released by brettanomyces/lactobacillus, one would presume that this has an impact on flavor/aromatic properties of the beverage. Because of this, I presume it would be hard to manage the amount of these compounds being released by such organisms. This therefore highlights the importance of pitching them at proven proportions both with respect to saccharomyces and other species, as well as in proportion to the amount of wort/must; the best way to control the release of these compounds would seemingly be accomplished by limiting the amount of substrate available to brettanomyces/lactobacillus via competition with other organisms such as sacch.




Other than temperature, factors such as ABV% will affect cell membrane fluidity, and therefore the cells' ability to carry out it's biological functions. This is why ABV ranges must also be respected for strains of yeast.

Again, the sensitivity of brettanomyces/lactobacillus to such factors is not well understood.

Cheers,

Delaney
 

Kaiser

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thanks for posting this.

Another reason why temperature fluctuations, at least during primary fermentation, are bad is that the yeast metabolism is a finely tuned system of substrate pools and pathways. If that gets out of whack too much, for example through temperature swings, those pools of substrate may "overflow" and provide too much substrate into pathways that produce less desirable flavor compounds like higher alcohols or excessive esters.

Once the yeast is done growing and consumed most of the sugars temperature swings are not as bad anymore.

Kai
 
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Delaney

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thanks for posting this.

Another reason why temperature fluctuations, at least during primary fermentation, are bad is that the yeast metabolism is a finely tuned system of substrate pools and pathways. If that gets out of whack too much, for example through temperature swings, those pools of substrate may "overflow" and provide too much substrate into pathways that produce less desirable flavor compounds like higher alcohols or excessive esters.

Once the yeast is done growing and consumed most of the sugars temperature swings are not as bad anymore.

Kai
Thanks,

I should clarify that the professor in question did not say whether or not this is the primary/sole reason that temperature fluctuations might impact yeast/bacteria activity, he simply confirmed that it would affect the functions/cycle of the yeast. For example reproduction might be affected...
 
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Delaney

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thanks for posting this.

Another reason why temperature fluctuations, at least during primary fermentation, are bad is that the yeast metabolism is a finely tuned system of substrate pools and pathways. If that gets out of whack too much, for example through temperature swings, those pools of substrate may "overflow" and provide too much substrate into pathways that produce less desirable flavor compounds like higher alcohols or excessive esters.

Once the yeast is done growing and consumed most of the sugars temperature swings are not as bad anymore.

Kai
Despite what you are suggesting (which I inquired about), Dr.Merwe suggested that temperature fluctuations within the yeast's tolerable range would not negatively impact primary fermentation, as this would not impart significant heat/cold stress. Again, this is only certain for saccharomyces, and not brettanomyces/lactabacillus.
 

Wynne-R

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temperature fluctuations within the yeast's acceptable temperature range will not produce ill-effects
Can somebody define this range?
 

Curtis2010

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Thanks for posting all the detail. Maybe should be put in a brewing science wiki here.

Important to keep in mind relative to ferm temps that all those hordes of feeding yeasty beasties generate a lot of heat. I've checked temp on ferms and found the wort temp 10F higher than the ambient temp. So, it would be easy to set ambient temp within range for the yeast strain and have the heat of ferm push the wort temp beyond that range -- possibly resulting in off flavors.

Your post also confirms that even for ale yeast the lower end of their temp range produces fewer off flavors. I've suspected this was ture, and am planning to start fermenting ales at the lower end of their temp ranges. I expect this is especially important during early very active fermentation when yeast activity produces heat.

Thanks.
 

tgmartin000

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What's considered a "fluctuation"? From what I understand, both the rate and magnitude of the temp swing is what matters. For instance, a swing up of 5 degrees in five days may be beneficial, whereas five degrees in five hours is probably pretty bad.
 
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Delaney

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Can somebody define this range?
This is specific to the strain of yeast you are using...In other words, there will be different temperature ranges for different strains. Therefore it is important to respect the range provided by the yeast supplier.

For example, lager yeasts require cold temperatures, whereas ale yeasts require warmer temperatures. It is more specific than this, however. Different ale yeasts will have different temperature ranges.

Important to keep in mind relative to ferm temps that all those hordes of feeding yeasty beasties generate a lot of heat. I've checked temp on ferms and found the wort temp 10F higher than the ambient temp. So, it would be easy to set ambient temp within range for the yeast strain and have the heat of ferm push the wort temp beyond that range -- possibly resulting in off flavors.

Your post also confirms that even for ale yeast the lower end of their temp range produces fewer off flavors. I've suspected this was ture, and am planning to start fermenting ales at the lower end of their temp ranges. I expect this is especially important during early very active fermentation when yeast activity produces heat.

Thanks.
Yes, this is important to note. The temperature range of a yeast does not refer to the ambient temperature. Fermentation generates heat, therefore one must pay attention to the temperature of the beer/wine, and not the room temperature.


From what I understand, it is more beneficial to ferment at lower temps because this will result in less volatile compounds (aromatic/flavor) from evaporating. As long as you do not exceed the temperature range for the yeast in question, I do not believe that off flavors would be produced. It would taste different, however, because you would have evaporated volatile compounds that would not have been lost at lower temperatures. Unless you have precise temperature regulation, you would probably want to stick to the lower end, in the event that temperature might fluctuate and go beyond the acceptable range.
There are always exceptions to these rules, as Dr.Merwe pointed out...for example one wants autolysis to occur, to a limited extent, in sparkling wines. Perhaps some beers would fare better without some of these volatile compounds?


PS: what part of Guate you at? I spent 6 months travelling throughout the land of eternal spring. What a beautiful place. Got kinda tired of Gallo though :).

What's considered a "fluctuation"? From what I understand, both the rate and magnitude of the temp swing is what matters. For instance, a swing up of 5 degrees in five days may be beneficial, whereas five degrees in five hours is probably pretty bad.

A fluctuation means a change in temperature...I would not be worried about the rate of temperate fluctuations, unless you are fermenting a small amount of beer (1 gallon). Large volumes of beer (5 gallons +) have a greater mass, therefore it requires much more heat to raise/lower the temperature of the liquid. Perhaps a very fast rate of temperature fluctuation would temporarily inhibit the biological functions of yeast cells, but I believe this would require a drastic difference between ambient and solution temperature.

As far as I'm aware temperature swings are not going to be beneficial. If the fluctuation is within the yeast's tolerable temperature range, however, it won't be detrimental, other than perhaps losing some of the more volatile compounds at higher temps.
 

Curtis2010

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This is specific to the strain of yeast you are using...In other words, there will be different temperature ranges for different strains. ...

Yes, this is important to note. The temperature range of a yeast does not refer to the ambient temperature. Fermentation generates heat, therefore one must pay attention to the temperature of the beer/wine, and not the room temperature.


From what I understand, it is more beneficial to ferment at lower temps because this will result in less volatile compounds (aromatic/flavor) from evaporating. As long as you do not exceed the temperature range for the yeast in question, I do not believe that off flavors would be produced. ......

PS: what part of Guate you at? I spent 6 months travelling throughout the land of eternal spring. What a beautiful place. Got kinda tired of Gallo though :).
...

Yes, Guate is a beautiful country. I live on the Rio Dulce which is on the Caribbean coast, so temperature control for brewing is a necessity (the highlands would probably be ideal for brewing). Too warm here on the Rio even to brew ales in the "winter" (now). It's not quite 9AM yet, and the ambient temp is 75F (pleasantly cool for here, YTD low= 71F, high = 92F). I use a couple of chest freezers with external thermostats for fermenting and a mix of corny kegs and carboys are fermentors.

So, based upon my past experience and this discussion here is what I plan to do for future ale ferm temps. I bank US-05 and use it for most general ale brewing so I'm assuming US-05. Temp ranges for US-05 per Fermentis are 12-25°C (53.6-77°F) ideally 15-22°C (59-71.6°F). By "ambient temp" in this context I mean the temp inside the cooler.

1. Chill wort to 75F and pitch yeast. (This a challenge to do here since my "cooling" water is about 80F, but I have a pre-chiller on the drawing board).

2. Set cooler thermostat to 54 and move fermentor to cooler. (My thought process here is that by the time ferm is active then the wort should be at or near ambient temp and if ferm activity increases wort temp by even as much as 10F then wort will still only be at 64F which is right in the "ideal" range.)

3. As very active primary fermentation subsides, gradually (2F per day) raise ambient temp to 60F and leave it there for the duration of fermentation (as determined by SG readings). I think that even less active ferm will raise the temp a few degrees so ambient of 60F should keep wort within ideal range without risking getting it too cool.

I plan to check wort temps along the way to confirm this strategy works.


Sound like a good plan?
 

Wynne-R

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In the book “Yeast” Chris White and Jamil Zainasheff suggest pitching a couple of degrees below your target and letting it drift up to the target temp over 18 - 36 hours. Hold it steady until the fermentation is 2/3 - 3/4 done, then increase it 4-10F over the course of a day or two.

Their rationale is that the flavor compounds are mostly done, but increasing the yeast metabolism will allow them reduce intermediary compounds and attenuate more fully.

So in the case of US-05, we could start at 62°F, let it increase to 64, hold it for a couple of days and then ramp it up to 70°F. Hold it there until you think it’s done.

My interest is in how tight the optimum temperature regulation should be. In my experience ± 1°F is better than ± 3°F. This is actual wort temperature, measured with a thermowell.
 
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Delaney

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Yes, Guate is a beautiful country. I live on the Rio Dulce which is on the Caribbean coast, so temperature control for brewing is a necessity (the highlands would probably be ideal for brewing). Too warm here on the Rio even to brew ales in the "winter" (now). It's not quite 9AM yet, and the ambient temp is 75F (pleasantly cool for here, YTD low= 71F, high = 92F). I use a couple of chest freezers with external thermostats for fermenting and a mix of corny kegs and carboys are fermentors.

So, based upon my past experience and this discussion here is what I plan to do for future ale ferm temps. I bank US-05 and use it for most general ale brewing so I'm assuming US-05. Temp ranges for US-05 per Fermentis are 12-25°C (53.6-77°F) ideally 15-22°C (59-71.6°F). By "ambient temp" in this context I mean the temp inside the cooler.

1. Chill wort to 75F and pitch yeast. (This a challenge to do here since my "cooling" water is about 80F, but I have a pre-chiller on the drawing board).

2. Set cooler thermostat to 54 and move fermentor to cooler. (My thought process here is that by the time ferm is active then the wort should be at or near ambient temp and if ferm activity increases wort temp by even as much as 10F then wort will still only be at 64F which is right in the "ideal" range.)

3. As very active primary fermentation subsides, gradually (2F per day) raise ambient temp to 60F and leave it there for the duration of fermentation (as determined by SG readings). I think that even less active ferm will raise the temp a few degrees so ambient of 60F should keep wort within ideal range without risking getting it too cool.

I plan to check wort temps along the way to confirm this strategy works.


Sound like a good plan?
The only way to know for sure is to try it and see what ferm temps you get with that system...

That being said, depending on the volume you are fermenting, I suspect that the process of cooling in your system would be relatively slow. The greater the difference in temperature between your solution (wort) and the surroundings, the faster it cools. Inversely, the less of a difference between these temperatures, the slower it cools. The difference in temperature you are mentioning is not great, therefore I'd assume it would be a slow process to cool the wort from 75F.

Furthermore, if you pitch at a good ratio, active fermentation can start very quickly..it would likely raise the temp of your wort by at least 5F. So in my opinion, you risk having your wort exceed the tolerable temperature range for your yeast, causing heat stress.


Perhaps you should investigate other yeast strains for ales which are tolerant of slightler higher temperatures given your predicament? Again, you will have to experiment and carefully monitory the temperature of your wort/beer to be certain.



PS: I've been to Rio Dulce. A friend of mine owns some forest along the coast between there and livingston. We went out there in one of those ghetto taxi boats and got smashed on coco loco. Good times, hot as hell out there and not much infrastructure, so I can definitely relate to the difficulties you'd face.
 
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Delaney

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In the book “Yeast” Chris White and Jamil Zainasheff suggest pitching a couple of degrees below your target and letting it drift up to the target temp over 18 - 36 hours. Hold it steady until the fermentation is 2/3 - 3/4 done, then increase it 4-10F over the course of a day or two.

Their rationale is that the flavor compounds are mostly done, but increasing the yeast metabolism will allow them reduce intermediary compounds and attenuate more fully.

So in the case of US-05, we could start at 62°F, let it increase to 64, hold it for a couple of days and then ramp it up to 70°F. Hold it there until you think it’s done.

My interest is in how tight the optimum temperature regulation should be. In my experience ± 1°F is better than ± 3°F. This is actual wort temperature, measured with a thermowell.
Interesting. I'd imagine that some of the most volatile compounds would still be lost as a result of raising the temp to 70F, but this would also likely be minimized due to a less active fermentation. This logic seems reasonable.

I don't understand what you mean by the optimum temperature. The optimum temperature for a given yeast strain is anything within the range for that species...I'd imagine that you would achieve different results at different temperatures within that range, so "optimum" temperature would really depend upon what you are striving for...

Intuitively I'd imagine that minimizing the fluctuations in temperature would produce a more specific flavor, whereas greater fluctuations would provide a slightly broader range of compounds. Is one better than the other? Depends what you want...I also imagine that the degree of variance would depend on the strain in question. For example, pseudo-lager strains produce a lager-like flavor at the lower end of their range and more of an ale-like flavor at the higher end. This would be an example of high variance within the range of tolerable temperatures....whereas other strains might display less variance.
 

Kaiser

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My interest is in how tight the optimum temperature regulation should be. In my experience ± 1°F is better than ± 3°F. This is actual wort temperature, measured with a thermowell.
+/-1 is better than +/-3 IMO.

It's important how this temperature is measured. If its measured with a thermowell you can set a fairly small band (+/-1, for example) if it’s the ambient temperature of the fermentation room you want a broader band to prevent your cooling compressor from cycling too frequently.

Note that there is nothing wrong with controlling the ambient temperature as long as it is chosen such that the fermentation temp peaks at the desired temp. There is also nothing wrong with temp swings in the ambient temp since the thermal mass of the beer will even them out.

I, for example, set my freezer chest to 6.5 C when brewing lagers. The fermentation activity will raise the temp to ~8.0 C. When I then see the beer temp fall again I know fermentation slows down and I can raise the ambient temp.

Kai
 

Wynne-R

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I am regulating the temperature of a six gallon water bath that a 5 gal carboy is setting in. For years I did this by adding ½ liter water bottles to the bath. Recently I figured out how to automate the process with a controller. It does a good job of regulating the water ± .3°C. That translates into ± .1°C in the beer, measured with a thermowell.

There are some vagaries in the process of regulating the water temperature with overshoot, stratification and circulation, but that probably works in my favor.

Interesting that Delaney mentioned “ a more specific flavor, whereas greater fluctuations would provide a slightly broader range of compounds.”
It’s hard to describe a flavor,but that’s a pretty good description of what I’m finding.

Oh, and I guess you figured it out, but I said ‘optimum temperature regulation’ not optimum temperature. It’s interesting, based on your comment that in some circumstance it might be advisable to increase the differential. Seems counterintuitive.

More research is required.
 
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Delaney

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More research is required.
Maybe this is just symantics but I'd call it experimentation not research. No matter how much research is done, I imagine that optimal temperature regulation would vary between yeast strains, styles of beer, and individual recipes. Perfection would require experimentation regardless, unless it is a proven recipe.

This is getting pretty nit-picky though...I imagine that in the context of homebrewing, many of us would probably have a hard time discerning the difference between a beer produced with temperature regulation ± .3°C vs. ± .1°C. Perhaps I'm wrong, just my guess. Either way, this is all good food for thought..for me at least.
 

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I have some aluminum tape and used that to fix my probe to a little piece of insulation. It is only about a quarter inch thick. The silver looking stuff that made to go around heat ducts and you see people wrapping kettles in. I put the aluminum tape side against the fermenter and have a strap that cinches it on pretty tight against the glass carboy. Typically I'll set my controller 5F lower than what I want. My FG sample sits close by with the hydrometer still in it and I start adjusting up depending on what that is doing. The sample is usually warmer than the fermenter so it will go faster anyhow. Short of a thermal well it is about the best I figure I can do for now.
 
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