It’s the age-old debate. Leave the kettle trub in the kettle and risk losing wort OR carry everything over and risk a cloudy looking beer!
WHAT IS KETTLE TRUB?
Kettle trub is the name given to the particulate matter that falls out of solution at the end of the brewing process. It mainly comprises of proteins from grain that have been damaged (or denatured) during the boil and so coagulate to form and insoluble mass of material. Along with this trub may also contain hop material, lipids from grain and trace minerals such as calcium and magnesium.
DO WE NEED TO REMOVE BEFORE FERMENTATION?
There’s an old saying that has the acronym SISO (if you’re not sure what I mean search the Urban dictionary for this phrase) that might lead you to believe that if you put a cloudy, murky-looking beer into the fermentor, that’s exactly what will come out of the other side. However, as we already know, not everything is as it seems in the world of brewing, least of all when yeast are added to the equation. As a part of the yeast life-cycle they produce compounds called ‘floculins’ which are used to stick yeast cells together to form clumps. These compounds don’t just stick yeast to yeast, they can also stick yeast to trub. So, beers that have a lot of trub carried over into the fermentor have actually been known to clear more quickly and have a much firmer ‘yeast cake’ at the end of fermentation. This can actually aid clarity and help to reduce beer loss when racking or bottling. Furthermore, beers that are dosed with trub (i.e. purposefully had trub added to them) have been seen to start fermenting much quicker than the same beer without the added trub. The scientific basis of this is unclear, I am personally of the opinion that the increased particulate simply gives gas bubbles a surface on which to form which gives the impression of a more vigorous fermentation. However, some suggest that the yeast may be able to benefit from having access to a protein and mineral-rich substance like trub.
That being said, regardless of whether or not yeast are able to make use of this material, it does contain lots of denatured and damaged lipids and proteins. When boiled, these compounds can react with oxygen and, over time may go on to react further with other compounds causing oxidative damage or oxidation in finished beer.
It seems to me, therefore, that residual kettle trub does not hurt clarity or fermentation but rather it may actually help both. It seems that the possible downstream deleterious effects of kettle trub may be able to be avoided by including some trub at the beginning of fermentation and racking the beer once the yeast cake has formed. I can say one thing with certainty here though: no matter how it might look, kettle trub is not the new secret ingredient in a New England IPA.