So, everything I read said to get the knox to 170 but do not boil. I was so afraid of boiling I only got it to about 130. Is this bad?
Boiling somehow destroying the function of gelatin is a common misconception that people who are largely unfamiliar with protein science tend to have. As a molecular scientist who works in protein chemistry in the Bay Area, I can tell you outright that boiling the gelatin will not affect the performance. 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.
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.
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/cells. The positive charge arises NOT because of structure, but because:
- the pH is slightly higher than the pKa of side chains (carboxylic acids) 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 sidechains (primary and secondary amines) 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.
So, if you have been boiling your gelatin, fear not. It should have no affect on the ability of gelatin to fine your beer. The pH of your beer (it will be more acidic than in the kettle if you fermented at all) and the temperature at which you store the beer after adding the finings (< 40F prefferably) are the 2 most important factors. Also, I would only cool the dissolved gelatin to ~70 F and then add. Cool it down too much before adding to beer, and you'll end up with jello.
