Happy HolidaySs Giveaway - Winners Re-Re-Re-Drawn - 24 hours to Claim!

Get your HBT Growlers, Shirts and Membership before the Rush!


Home Brew Forums > Home Brewing Beer > Brew Science > Cell membranes and temperature fluctuations
Reply
 
LinkBack Thread Tools
Old 01-14-2013, 03:45 AM   #1
Delaney
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2011
Location: Montreal, Quebec
Posts: 493
Liked 14 Times on 14 Posts
Likes Given: 16

Default Cell membranes and temperature fluctuations

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

__________________
Delaney is offline
 
Reply With Quote Quick reply to this message
Old 01-14-2013, 02:45 PM   #2
Delaney
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2011
Location: Montreal, Quebec
Posts: 493
Liked 14 Times on 14 Posts
Likes Given: 16

Default

Updated first thread

__________________
Delaney is offline
 
Reply With Quote Quick reply to this message
Old 01-14-2013, 03:45 PM   #3
Kaiser
Feedback Score: 0 reviews
 
Kaiser's Avatar
Recipes 
 
Join Date: Nov 2005
Location: Pepperell, MA
Posts: 3,904
Liked 114 Times on 71 Posts
Likes Given: 4

Default

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

Kaiser is offline
 
Reply With Quote Quick reply to this message
Old 01-15-2013, 05:25 AM   #4
Delaney
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2011
Location: Montreal, Quebec
Posts: 493
Liked 14 Times on 14 Posts
Likes Given: 16

Default

Quote:
Originally Posted by Kaiser View Post
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...
__________________
Delaney is offline
 
Reply With Quote Quick reply to this message
Old 01-15-2013, 08:17 PM   #5
Delaney
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2011
Location: Montreal, Quebec
Posts: 493
Liked 14 Times on 14 Posts
Likes Given: 16

Default

Updated earlier post with more info!
__________________
Delaney is offline
 
Reply With Quote Quick reply to this message
Old 01-15-2013, 08:22 PM   #6
Delaney
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2011
Location: Montreal, Quebec
Posts: 493
Liked 14 Times on 14 Posts
Likes Given: 16

Default

Updated earlier post

__________________
Delaney is offline
 
Reply With Quote Quick reply to this message
Old 01-15-2013, 08:24 PM   #7
Delaney
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2011
Location: Montreal, Quebec
Posts: 493
Liked 14 Times on 14 Posts
Likes Given: 16

Default

Quote:
Originally Posted by Kaiser View Post
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.
__________________
Delaney is offline
 
Reply With Quote Quick reply to this message
Old 01-16-2013, 01:25 AM   #8
Wynne-R
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2009
Location: Texas
Posts: 914
Liked 99 Times on 64 Posts
Likes Given: 82

Default

Quote:
temperature fluctuations within the yeast's acceptable temperature range will not produce ill-effects
Can somebody define this range?
__________________
Wynne-R is offline
 
Reply With Quote Quick reply to this message
Old 01-16-2013, 01:51 AM   #9
Curtis2010
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
Curtis2010's Avatar
Recipes 
 
Join Date: Dec 2011
Location: , Guatemala
Posts: 1,110
Liked 98 Times on 65 Posts
Likes Given: 1

Default

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.

__________________
Curtis2010 is offline
 
Reply With Quote Quick reply to this message
Old 01-16-2013, 02:41 AM   #10
tgmartin000
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2011
Location: Denver, CO
Posts: 1,013
Liked 64 Times on 51 Posts
Likes Given: 19

Default

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.

__________________
tgmartin000 is offline
 
Reply With Quote Quick reply to this message
Reply



Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Kegerator temperature fluctuations buzzbromp Beginners Beer Brewing Forum 4 07-01-2012 06:55 PM
temperature fluctuations Tiredboy Beginners Beer Brewing Forum 3 04-17-2012 04:55 PM
Temperature fluctuations PickledFetus Fermentation & Yeast 6 10-19-2011 04:15 PM
How bad is temperature fluctuations? codeblue2k General Beer Discussion 9 02-18-2011 04:39 AM
Temperature fluctuations NWPAbrewer Beginners Beer Brewing Forum 1 07-08-2008 10:31 AM



Newest Threads

LATEST SPONSOR DEALS