Can someone please explain "Cold Crashing"?

[Crew]

soluble is to be dissolved in a liquid to make a homogeneous solution (the smallest of particle size mixture) yeast is microscopic, that's why its soluble.. the basic idea is dissolved to where you cant tell where yeast is specifically.. with kids in a pool, you can pick them out (heterogeneous)

 

[Crew]

most microscopic particles are soluble

 

[ayoungrad]

But cold crashing is a term developed to define a pre final packaging way of accomplishing this...

This actually clears it up (no pun intended) for me. I always thought cold crashing was defined as ramping the temperature down to clear beer. I did not realize it was a term specific to pre-packaging.

 

[Bobby_M]

I agree with AnoldUR in that chilling beer is useful for different reasons throughout our processes but the specific term cold crashing is really specific to chilling cloudy post fermented beer in order to get it to drop clear faster than if you left it at ferment temps. I wouldn't get all excited if someone called in-bottle refrigeration "cold crashing" but I just don't think the term fits. If you don't cold crash in primary/secondary, you'd just wait an extra week to let it clear or package it cloudy.

 

[StittsvilleJames]

Now that this has been brought up, I'm having a hard time understanding what being "soluble" means. Yeasts are organisms. Are organisms soluble? By your statement it appears that somehow, yes, this is possible. Where I'm having a problem is that it seems that there's a corollary, and that is that a swimming pool full of kids are water soluble because they're in the pool. What is the distinction that makes yeast soluble but children not?

What am I missing?

Well, if you are missing any children, I would try cold crashing your pool...

 

[dizzyag]

As to the bad chemist argument, I believe the yeast in solution would be more akin to a colloidal suspension than a dissolution.

 

[gr8shandini]

soluble is to be dissolved in a liquid to make a homogeneous solution (the smallest of particle size mixture) yeast is microscopic, that's why its soluble.. the basic idea is dissolved to where you cant tell where yeast is specifically.. with kids in a pool, you can pick them out (heterogeneous)

Not quite. A solution happens at a molecular level. Yeast may be small, but they're way bigger than molecules. That's why you can filter the yeast out of your beer, but not any dissolved salts / gases.

Yeast floating in beer is a colloidal suspension, not a solution.

http://en.wikipedia.org/wiki/Colloid

Edit: Damn, dizzy beat me to the punch

 

[dizzyag]

Perhaps what happens in a cold crash is as the fluid is cooled the movement of the molecules slows as the liquid comes closer to what would be the freezing point. This reduction of kinetic energy might allow the larger particles of yeast being held in a colloidal suspension to fall out of "solution".

 

[simtel20]

Not quite. A solution happens at a molecular level. Yeast may be small, but they're way bigger than molecules. That's why you can filter the yeast out of your beer, but not any dissolved salts / gases.

Yeast floating in beer is a colloidal suspension, not a solution.

http://en.wikipedia.org/wiki/Colloid

Edit: Damn, dizzy beat me to the punch

From the wikipedia article, it follows that the yeast falling out of the suspension is called flocculation in general, it matches the action in a collodial suspension. We have a winner! Dizzy and you.

 

[LVBen]

Not quite. A solution happens at a molecular level. Yeast may be small, but they're way bigger than molecules. That's why you can filter the yeast out of your beer, but not any dissolved salts / gases.

Yeast floating in beer is a colloidal suspension, not a solution.

http://en.wikipedia.org/wiki/Colloid

Edit: Damn, dizzy beat me to the punch

The information on that link is about molecules at gas, liquid, and solid states. The yeast cells are obviously in suspension, but I don't see anything that says that they are colloids. Do you have any link to something that says that organisms can be colloids or more specifically that yeast are colloids? Are humans colloids when we are swimming in the ocean or swimming pools? That Wikipedia link says that organisms can have colloids inside of them, but since organisms are made up of multiple molecules with liquid, solid, and gas inside of us, I don't see how that link is relevant.

The yeast will eventually drop out of suspension whether we crash cool or not. Cooling just makes it faster, because it decreases the amount of movement, making it more difficult for the cells to swim and drift upwards. If there is sugar left for the yeast, they'll stop eating it, and they will also no longer be creating the CO2 that helps them rise up into suspension.

To Crew, I didn't say that ions were soluble. I said that the salts we use in brewing are soluble. The temperature of the wort/beer certainly does affect the solubility of brewing salts and sugar.

 

[LVBen]

Just based on this part alone:

A colloid is a substance microscopically dispersed evenly throughout another substance.[1]

A colloidal system consists of two separate phases: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium). A colloidal system may be solid, liquid, or gaseous.

I'm going to go ahead and state that yeast is not a colloid. They are not a substance, they are an organism made up of different substances. They are not solid, liquid, or gas, but they do contain solids, liquids, and gases.

 

[dizzyag]

Since yeasts do not swim about, they act as a particle. A colloid is a particle that is held in suspension because they are small enough that the molecular movement keeps them in suspension at least for a relatively speaking very long time. So the key here is that they act in a fluid as a colloid. One of the tests for a colloidal suspension is to shine a directed light into the fluid and you should get the cone of light like headlights in the fog. This is not a philosophical debate as to "the meaning of life and colloids" simply a description of the physics of what is occurring in the most relative definable terms.

The eventual settling out of most the yeast could also be contributed to by other effects such as the yeasts hitting each other and sticking together making larger particles that settle out .

 

[dizzyag]

Here are a couple of papers on different colloidal and flocculation properties of yeast.

http://onlinelibrary.wiley.com/doi/10.1021/bp00021a005/abstract

https://circle.ubc.ca/handle/2429/31517

 

[cents]

...I'm having a hard time understanding what being "soluble" means...

Do not -- I repeat, DO NOT -- listen to Crew. It seems that you have a better understanding of "soluble" than he does. Yeast are in suspension, they are NOT dissolved.

 

[Dr1nkBeer]

I'm no chemist, but I'm given to understand that there is less activity in general at lower temperatures, all the way down. Your yeast would engage in less activity, which would produce less agitation of solids in solution. It should also have an influence on Brownian motion, which is molecules dancing their dance at the tiny level (that's technical talk)

I'm no Chemist.. cant believe nobody caught the humor in this...

My only question is do you drop the temp as low as you can get it without freezing or "Cold Crash" before you force carb? that is if your kegging?

I tend to get impatient and once my beer is kegged I blip the Co2 release any O2 in the head space then Crank it to 30 psi to rest for 30 hrs. It works out perfect.

My two cents to add: I tend to store my beers really cold only because I tend to let them sit out a little bit before drinking. I do the same with my keg fridge when i'm not actively using it. I bring the temp down to 32ish My IPA that i kegged pretty much cloudy about 2 months ago is so clear i can read a magazine through the pint... I didnt use any adjuncts. Now if my Wheat beer clears i'd be upset...

Someone mentioned dont freeze it... well a few Germans did just that and ended up with some REALLY good stuff. <Cough> Sink the Bizmarck... ring a bell? If any of my kegs froze i'd rack off into a second keg (before defrost started) just to see if the ABV would go up. And yes i have a bottle of this bizmarck.. and its worthy.

 

[gmcastil]

I'm a relatively new brewer, but I'm wiling to give a description of what solubility and colloids are. For the sake of simplicity, I'll assume water is the solvent.

From a practical sense, a substance is soluble if water will form a hydration shell around it. At a molecular level, this usually occurs because there are enough polar sites which are able to hydrogen bond with water. Things like carbohydrates, most proteins, and ions are all soluble to varying degrees in water. Most lipids are generally insoluble in water due to their relative lack of polar groups.

I'm not really going to try and get into a detailed discussion on the physics of what really drives solvation, because it requires a rather subtle and complicated discussion of entropy and how it relates to the Gibbs free energy of a particular reaction. Suffice to say that, if the most energetically favorable configuration for a compound in the solution is to be surrounded by a bunch of H2O molecules, then that is what will occur. Solubility for a molecule is, in general, a function of several variables, temperature being one of them.

As to the discussion of whether a mixture of beer and yeast is a solution or a colloid, I would submit that it is neither. One of the defining characteristics of a colloid is that it doesn't settle, so by inspection we can see that is clearly not the case here. I suppose that one could make try to make the case for yeast to be dissolved in water, but that also doesn't explain the fact that eventually, the yeast will form a layer at the bottom of the container.

It's probably most accurate to look at the yeast / beer mixture as a suspension. The insoluble yeast cells appear to be dissolved because one can't seem them without a microscope. However, given a constant temperature, no turbulence or convection in the fluid, and eventually, the cells will sediment. You can see this phenomenon with liquid yeast vials as well as the carboy after a week or two of fermentation. The reason that the yeast cake hardens like a previous poster mentioned is probably because water molecules trapped in the yeast cake eventually escape, although that is just a guess. Also, keep in mind that there is 5 gallons of dense liquid on top of it, so after a while, the force of the fluid above it compresses the yeast cake into a rather compact state.

Another example of this is blood. Blood is a suspension of erythrocytes (red blood cells), leukocytes (white blood cells), and platelets into which proteins and other macromolecules have been dissolved. If you take blood and put it in a centrifuge (or let it sit a long, long time), it will form three primary layers: the hematocrit (the red part), the buffy coat (the white part), and the plasma, which is the straw-colored solution that remains on top. Note that, during centrifugation, the red blood cells get pulled out of suspension, but the layer of dissolved substances (mostly proteins) remains a solution. The same thing happens to beer, it just doesn't need a centrifuge to get all of the particles to drop out of suspension.

I'm going to lean over the plate here and proffer a hypothesis on cold crashing. My suspicion is that cold crashing beer accomplishes the same thing that centrifugation does for blood, which is namely to separate the insoluble particles (yeast, particulates, etc.) from the rest of the solution. The drop in temperature probably aids in this by reducing the overall kinetic energy of the molecules in the liquid and accelerating the rate at which particles drop out of suspension. I think that if one were to allow the beer to sit for an exceedingly long time, maybe a year, the result would be the same - as far as the suspension goes. No doubt the taste would be affected, which probably explains why cold crashing is practiced.

One final thought - as a previous poster mentioned, solubility is also a function of temperature. So, in addition to accelerating the rate that particles drop out of suspension, it's entirely possible that dissolved proteins, sugars, and other soluble compounds would also be forced out of solution as well. So, it wouldn't surprise me to find that, after cold crashing, the yeast cake has all sorts of soluble bits in it as well.

 

[muthafuggle]

I'm a relatively new brewer, but I'm wiling to give a description of what solubility and colloids are. For the sake of simplicity, I'll assume water is the solvent.

From a practical sense, a substance is soluble if water will form a hydration shell around it. At a molecular level, this usually occurs because there are enough polar sites which are able to hydrogen bond with water. Things like carbohydrates, most proteins, and ions are all soluble to varying degrees in water. Most lipids are generally insoluble in water due to their relative lack of polar groups.

I'm not really going to try and get into a detailed discussion on the physics of what really drives solvation, because it requires a rather subtle and complicated discussion of entropy and how it relates to the Gibbs free energy of a particular reaction. Suffice to say that, if the most energetically favorable configuration for a compound in the solution is to be surrounded by a bunch of H2O molecules, then that is what will occur. Solubility for a molecule is, in general, a function of several variables, temperature being one of them.

As to the discussion of whether a mixture of beer and yeast is a solution or a colloid, I would submit that it is neither. One of the defining characteristics of a colloid is that it doesn't settle, so by inspection we can see that is clearly not the case here. I suppose that one could make try to make the case for yeast to be dissolved in water, but that also doesn't explain the fact that eventually, the yeast will form a layer at the bottom of the container.

It's probably most accurate to look at the yeast / beer mixture as a suspension. The insoluble yeast cells appear to be dissolved because one can't seem them without a microscope. However, given a constant temperature, no turbulence or convection in the fluid, and eventually, the cells will sediment. You can see this phenomenon with liquid yeast vials as well as the carboy after a week or two of fermentation. The reason that the yeast cake hardens like a previous poster mentioned is probably because water molecules trapped in the yeast cake eventually escape, although that is just a guess. Also, keep in mind that there is 5 gallons of dense liquid on top of it, so after a while, the force of the fluid above it compresses the yeast cake into a rather compact state.

Another example of this is blood. Blood is a suspension of erythrocytes (red blood cells), leukocytes (white blood cells), and platelets into which proteins and other macromolecules have been dissolved. If you take blood and put it in a centrifuge (or let it sit a long, long time), it will form three primary layers: the hematocrit (the red part), the buffy coat (the white part), and the plasma, which is the straw-colored solution that remains on top. Note that, during centrifugation, the red blood cells get pulled out of suspension, but the layer of dissolved substances (mostly proteins) remains a solution. The same thing happens to beer, it just doesn't need a centrifuge to get all of the particles to drop out of suspension.

I'm going to lean over the plate here and proffer a hypothesis on cold crashing. My suspicion is that cold crashing beer accomplishes the same thing that centrifugation does for blood, which is namely to separate the insoluble particles (yeast, particulates, etc.) from the rest of the solution. The drop in temperature probably aids in this by reducing the overall kinetic energy of the molecules in the liquid and accelerating the rate at which particles drop out of suspension. I think that if one were to allow the beer to sit for an exceedingly long time, maybe a year, the result would be the same - as far as the suspension goes. No doubt the taste would be affected, which probably explains why cold crashing is practiced.

One final thought - as a previous poster mentioned, solubility is also a function of temperature. So, in addition to accelerating the rate that particles drop out of suspension, it's entirely possible that dissolved proteins, sugars, and other soluble compounds would also be forced out of solution as well. So, it wouldn't surprise me to find that, after cold crashing, the yeast cake has all sorts of soluble bits in it as well.

*slow clap*

This needs to be added to the wiki!

 

[StittsvilleJames]

I'm a relatively new brewer, but I'm wiling to give a description of what solubility and colloids are. For the sake of simplicity, I'll assume water is the solvent.

From a practical sense, a substance is soluble if water will form a hydration shell around it. At a molecular level, this usually occurs because there are enough polar sites which are able to hydrogen bond with water. Things like carbohydrates, most proteins, and ions are all soluble to varying degrees in water. Most lipids are generally insoluble in water due to their relative lack of polar groups.

I'm not really going to try and get into a detailed discussion on the physics of what really drives solvation, because it requires a rather subtle and complicated discussion of entropy and how it relates to the Gibbs free energy of a particular reaction. Suffice to say that, if the most energetically favorable configuration for a compound in the solution is to be surrounded by a bunch of H2O molecules, then that is what will occur. Solubility for a molecule is, in general, a function of several variables, temperature being one of them.

As to the discussion of whether a mixture of beer and yeast is a solution or a colloid, I would submit that it is neither. One of the defining characteristics of a colloid is that it doesn't settle, so by inspection we can see that is clearly not the case here. I suppose that one could make try to make the case for yeast to be dissolved in water, but that also doesn't explain the fact that eventually, the yeast will form a layer at the bottom of the container.

It's probably most accurate to look at the yeast / beer mixture as a suspension. The insoluble yeast cells appear to be dissolved because one can't seem them without a microscope. However, given a constant temperature, no turbulence or convection in the fluid, and eventually, the cells will sediment. You can see this phenomenon with liquid yeast vials as well as the carboy after a week or two of fermentation. The reason that the yeast cake hardens like a previous poster mentioned is probably because water molecules trapped in the yeast cake eventually escape, although that is just a guess. Also, keep in mind that there is 5 gallons of dense liquid on top of it, so after a while, the force of the fluid above it compresses the yeast cake into a rather compact state.

Another example of this is blood. Blood is a suspension of erythrocytes (red blood cells), leukocytes (white blood cells), and platelets into which proteins and other macromolecules have been dissolved. If you take blood and put it in a centrifuge (or let it sit a long, long time), it will form three primary layers: the hematocrit (the red part), the buffy coat (the white part), and the plasma, which is the straw-colored solution that remains on top. Note that, during centrifugation, the red blood cells get pulled out of suspension, but the layer of dissolved substances (mostly proteins) remains a solution. The same thing happens to beer, it just doesn't need a centrifuge to get all of the particles to drop out of suspension.

I'm going to lean over the plate here and proffer a hypothesis on cold crashing. My suspicion is that cold crashing beer accomplishes the same thing that centrifugation does for blood, which is namely to separate the insoluble particles (yeast, particulates, etc.) from the rest of the solution. The drop in temperature probably aids in this by reducing the overall kinetic energy of the molecules in the liquid and accelerating the rate at which particles drop out of suspension. I think that if one were to allow the beer to sit for an exceedingly long time, maybe a year, the result would be the same - as far as the suspension goes. No doubt the taste would be affected, which probably explains why cold crashing is practiced.

One final thought - as a previous poster mentioned, solubility is also a function of temperature. So, in addition to accelerating the rate that particles drop out of suspension, it's entirely possible that dissolved proteins, sugars, and other soluble compounds would also be forced out of solution as well. So, it wouldn't surprise me to find that, after cold crashing, the yeast cake has all sorts of soluble bits in it as well.

I was just about to post this exact same thing.

 

[Dr1nkBeer]

I was just about to post this exact same thing.

 

[hbtasdfg]

yeast float in the beer due to brownian motion and movement of the water molecules. CO2 carries yeast upward too. Cold water molecules move less. As the water cools a couple things happen.

1. Less brownian motion as water molecules move less.

2. CO2 becomes MORE soluble as the temperature falls so motion generated by residual CO2 bubbling to the surface is reduced.

3. Yeast become inactive because they have evolved to do that for billions of years and clump together.

All three factors mean that basically the yeast all go to sleep and fall to the bottom of the bucket and stick together.

 

[helibrewer]

The water molecules also get closer together as they are cooled. Things in between these water molecules that are of any significant size, get "squeezed" out and settle to the bottom, very similar to mositure getting squeezed out of cold air to form clouds.

It's a pretty easy phenomenon to observe. Fill a carboy into the neck and then heat or cool it, you will see changes in volume do this change in spacing between the molecules.

 

[gmcastil]

1. Less brownian motion as water molecules move less.

2. CO2 becomes MORE soluble as the temperature falls so motion generated by residual CO2 bubbling to the surface is reduced.

Yes, this was pretty much what I was trying to explain, just didn't want to actually use the words Brownian motion.

 

[gmcastil]

The water molecules also get closer together as they are cooled.

This is mostly true, although below a certain temperature (~ 40F) the distance increases again. In general, solids are more dense than liquids, water being a rare exception. The reason for this involves hydrogen bonding of water molecules and a few other topics that aren't all that important.

 

[dienster]

I thought that the yeast got cold, huddled together for warmth and then were too dense to stay in suspension so fall out..

 

[ClarnoBrewer]

Here's an explanation of flocculation that is somewhat approachable (at least in parts) from Wyeast. They should know what they're talking about.
Wyeast Laboratories : Commercial : Breweries : Technical Information : Clarifiaction

 

[gmcastil]

Here's an explanation of flocculation that is somewhat approachable (at least in parts) from Wyeast. They should know what they're talking about.
Wyeast Laboratories : Commercial : Breweries : Technical Information : Clarifiaction

That's a really good link. Thanks. I had more or less treated yeast as a particulate - never occurred to me that they could be actively involved in the process of sedimentation. Thanks again.

 

[ClarnoBrewer]

That's a really good link. Thanks. I had more or less treated yeast as a particulate - never occurred to me that they could be actively involved in the process of sedimentation. Thanks again.

You're welcome. I don't necessarily understand all of it, but I figure the Wyeast folks should. The thing that I keep in mind, and that others have indicated, is that the yeast are organisms living in the liquid. While not motile, their life cycle does affect their place in the liquid. Much more like plankton moving in the water column than salts dissolved in liquid.

Having said that, I'm in over my head on most of this. They eat sugar and poop alcohol and CO2. That's why I love them. And as a previous poster pointed out, when they get cold, they all huddle together at the bottom! And we all know that sickness is caused by tiny imps living in your body...