Monday, 28 January 2013

Brewing Science: Gelatin & Clearing Beer

I was bottling my Merlins Mild this Friday, and while preping my gelatin, I realized it has been a while since I did an article on brewing science.  The two thoughts merged, leading to this article on how gelatin helps clear beer.

Firstly, a brief outline of how I use gelatin for fining my beer.  There are a lot of other methods out there, but this is what I have found works for me.
  1. Cool the beer as cold as you can (crash cooling), you can do this in a fermenter or keg.  The colder it is, the clearer the final beer will be.  I've had good results at 18-20C, but for crystal-clear beer you need to be at 5C or cooler.  Don't freeze it...
  2. In a lidded pot, add 1 packet (1 tablespoon) unflavoured gelatin to 250-350 ml (1 to 1.5 cup) boiled and cooled water (20C/room temp or colder).  Let sit 20 minutes to 'bloom'.  You'll notice that the gelatin will swell, from small prills to balls 0.5-1 mm in diameter.
  3. Heat gently, in a pot covered with a lid, to 77C (170F).  Remove from heat, keeping covered, and let cool to room temperature.
  4. Add to top of cold beer.
  5. In 2-3 days, beer should be super-clear.  You can bottle at this point.  If in a keg, you can begin carbing as soon as the gelatin is added.
Note that pre-boiling the water is optional, but this does sanitize the water.  It is important to add the gelatin to room temp or colder water for blooming - warmer than that will lead to clumping and incomplete blooming.  It is absolutely essential to heat to 77C; a little cooler and the gelatin will not solubilize, a little warmer and it will gel in your beer.

The science behind how this works can be found below the fold...

A Collagen
Helix (Fibre)
The secret behind gelatins function is in its chemistry.  Gelatin is produced from collagen, a protein found in the bones & skin of animals. Most gelatin comes form pigs and cows, but one form found in commercial brewing (isinglass) comes from the swim bladders of fish.

Collagen's main biological function is to provide strength to tissues - it is what makes your skin elastic. The need for this protein to be both strong and elastic requires some unique chemistry. This unique chemistry helps 3 collagen molecules come together to form helical bundles (left). It is these bundles that provide collagen with both rigidity and flexibility. Not clear in this image are the "sticky ends" which allow these bundles to assemble into long chains - that's OK, since the sticky ends have little to do with brewing.

Its the long helical part of collagen that is important for gelatin.  These helical sections are generally comprised of repeats of a few amino acids - specifically, -[glycine-proline-x]-, where x is an amino acid other than glycine/proline. This motif is repeated over 100 times in each helical portion of a collagen strand. Gelatin is produced by hydrolyzing (breaking) the collagen into shorter pieces - so instead of having this Gly-Pro-X repeated hundreds of times, you instead end up with small pieces in which it is repeated 2 to 5 times.

It is this breaking that is important - in collagen this triplet structure is key to forming the 3-protein helix:  glycines and prolines are hydrophobic - meaning they don't like water, while the 'X's tend to be either polar or charged residues - meaning they like water. In collagen the water-hating parts of one collagen molecule binds to the water-hating bits of two other molecules, causing the collagen to wrap around the water-hating parts, thus producing a helix which has all of the water-hating bits in the middle and the water-loving parts on the outside (where they are exposed to the water-filled environment of our bodies).

Breaking the collagen into short bits prevents this from happening.  When we bloom and heat the gelatin we solubilize the gelatin, meaning that we end up with single gelatin fragments (or small clusters) stably suspended in water. Heat too much and the molecules will condense  forming jello.  Heat too little and you don't solubilize the protein.  But warming to just the right point will solubilize this normally poorly soluble protein.

But the gelatin doesn't like this - it is very unnatural for those water-hating bits to be exposed to water. So when you add this to beer, it likes to stick to stuff - the water-hating bits will seek out water-hating bits of other proteins. The water-loving bits (especially the charged bits) will seek out molecules of the opposite charge. The end effect is the gelatin links together a lot of the charged and water-hating stuff in the beer - i.e. proteins & yeasts - causing them to form flocks which then settle out of the beer.

Given that, you may wonder why it works better in cold beer. The reason here has little to do with the gelatin, and instead has to do with the proteins and yeasts in solution. At warmer temperatures, water will tend to form 'hydration shells' around solubilized structures - i.e. a stable "shell" of water will associate with proteins, helping to keep them in solution. Due to some of the odder aspects of protein chemistry, these shells are less stable at lower temperatures - meaning they do not shield the proteins from the gelatin. As such, the gelatin has better access to the proteins (and yeasts), and thus are more able to clear the beer. In fact, this is what happens with chill haze - cooling of the beer brings the proteins out of solution; a small degree of aggregation occurs, making the beer cloudy. Gelatin, added to this cloudy solution, will further link these clumps together  allowing the aggregates to quickly fall out of solution.


  1. Great explanation of how to use gelatin and why it works.

  2. Thanks for the article. How much beer are you clearing with this 1 packet (1 tablespoon) of unflavoured gelatin? It's the only missing piece of the puzzle. It's likely 5 gallons but figured I'd ask/confirm.


    1. There is a slight typo above; you need a half packet to clear 5 imperial gallons (23L, ~6 US gal) of beer.

  3. You claim that gelatin will gel in the beer too much if you heat beyond 77C. Isn't this a myth?

    First of all, it actually says “Boil to dissolve” on LD Carlson Gelatin.

    I believe this is due in large part to two things:

    1) Gelatin is simply hydrolyzed collagen, and is often produced by boiling source material rich in collagen in a mild acid to encourage hydrolysis. Boiling is an actual step that speeds up hydrolysis that many manufacturers use in the production of gelatin.

    2) Collagen, and therefore gelatin, is a protein/peptide based material. So, while boiling (or even heating to 180 F) would affect the structure, the structure is not what results in the clearing effect seen with the use of gelatin as a fining agent. It is the charge of the gelatin molecule The approximate amino acid composition of gelatin is: glycine 21%, proline 12%, hydroxyproline 12%, glutamic acid 10%, alanine 9%, arginine 8%, aspartic acid 6%, lysine 4%, serine 4%, leucine 3%, valine 2%, phenylalanine 2%, threonine 2%, isoleucine 1%, hydroxylysine 1%, methionine and histidine <1% and tyrosine <0.5%.

    The clearing effect of gelatin arises due to the fact that, at the pH of beer, the collagen is highly positively charged, allowing it to bind to negatively charged molecules/free proteins/cell surface proteins. The positive charge arises NOT because of structure, but because:

    the pH is slightly higher than the pKa of carboxylic acid side chains on aspartic acid and glutamic acid, making them negatively charged, but only slightly so, as the pH of beer is only slightly higher than the pKa of these acid sidechains.
    the pH is significantly lower than the pKa of primary and secondary amines sidechains on proline, hydroxyproline, arginine, lysine, and hydroxylysine, making them very positively charged. The positive charge resulting from these residues is not only enough to offset the small amount of negative charge on the glutamic and aspartic acids, but it is sufficiently high enough to give a large positive charge to the overall gelatin molecules.
    The remainder of the amino acids in the structure have primarily hydrophobic side chains, and do not result in contribution to charge.

    1. Boiling does negatively effect the efficacy of gelatin, for the simplest of reasons. Above ~77C you denature the gelatin fragments sufficiently enough to completely denature the hydrophobic regions. These will then promote rapid gelatin aggregation once the solution begins to cool - this is the major mechanism by which gelatin forms into a gel (i.e. jello). But in beer this leads to the formation of gelatin blobs, which greatly reduces the surface area of gelatin available for adsorption of haze materials.

      Solubilized gelatin (i.e. heated to 70-77C) retains enough structure to limit aggregation while still exposing some of the poly-hydrophobic motifs of the collagen peptides. Because it remains soluble, it has a huge surface area compared to over-heated (and thus aggregated) gelatin, as the resulting beer-gelatin solution is a suspension of single gelatin molecules & minute gelatin aggregates. This gives you an absorptive area much, much larger than gelatin which has aggregated.

      Like most colloidal clearing agents, gelatin is amphipathic and functions by aggregating materials through a combination of hydrophobic and electrostatic interactions. Whether the electrostatic or hydrophobic elements dominate a clearing reaction depends on the target molecules; for carbohydrates its the electrostatics; for proteins (which is the bulk of haze) hydrophobicity is primarily responsible for clearance. You can use gelatin to precipitate proteins under conditions which otherwise eliminate electrostatic interactions (e.g. low or high pH, high salinity), with little loss in efficacy compared to conditions where electrostatic interactions occur.

      Moreover, most gelatins in grocery stores are type b gelatins, prepared by hydrolysis by acid and base, not by acid alone (acid hydrolysis limits the collagen sources used to prepare gelatin; base hydrolysis allows nearly any collagen-containing item to be converted into gelatin). B-type gelatin has a pI of 4.7-5.2; right in the pH range of beer. Or, in other words, gelatin in beer is largely unchanged. Type A (acid-only) gelatin has a much high pI and thus would be charged in beer; however, type A is somewhat of a specialty item as it tends to be more expensive and not overly useful as a food thickener/gel agent as it undergoes less crosslinking during cooling.

    2. His reply was basically a copy and paste from what biobrewer/theyeastbay said on beer advocate.

  4. Thank you, excellent explanation!