Ask The Brewmasters

On further discussion, this tank appears to be one in which they tried adding Tetra at terminal along with the finings (Biofine Clear @ 100ml/bbl). So it would have gone into a co2 atmosphere. Hmmm...

I think it's fair to assume this is almost certainly a result of adding tetrahydroiso-alpha acids at tank full (that is, pre-fermentation). Tetrahydro-IAAs are well known to give a very dense and stable foam when used as post-fermentation bittering, so it's not a stretch to think it would do the same during fermentation. You seem to be targeting about 10 bitter units, based on this data sheet, which also notes that even at "3-5 ppm, foam stand and lacing are significantly enhanced".

One of the reasons it's reccommended to use this post-maturation/clarification is that the molecule itself is much more surface-active than non-reduced IAAs (hence the higher foam activity). Basically, added at fermenter-full, the tetrahydro-IAAs will preferentially associate with evolving carbon dioxide bubbles (as well as fermenter walls, yeast cell walls, cold break and any other available surfaces) during primary. It's not necessarily precipitation, per-se (as in, it's not reacting chemically with something in the beer and coming out of solution), and so it doesn't really happen in the brite tank (unless you're getting lots of foam formation, such as with over-eager carbonation through a stone).

Also, the fact that it's a lager fermentation probably allowed the formation of what's essentially finished-beer foam, as there wouldn't have been nearly as much "floating" yeast at the beer/headspace interface to interfere (I feel like you can kind of see that in your fermentation yeast ring).

All in all, I think it's a pretty fair bet that what you're seeing is just dried-out, leftover, tetrahydro-IAA-enhanced foam from primary fermentation.

Ah, tetra and foam.  That takes me back.  Some rather interesting observations you can make on this.  As beer lacing is controlled largely by hops, consider the following figure from Evans and Bamforth 2009.  Think your tank, only smaller...  


Then consider the effect of over foaming with tetra.  On collapse you get these "foam-bergs." 

References:

Evans, D. E., And Bamforth, C.W. 2009. Beer foam: Achieving a suitable head. In: BAMFORTH, C. W., RUSSELL, I., AND STEWART, G.G. (ed.) Handbook of alcoholic beverages: Beer, a quality perspective. Burlington MA: Elsevier. pp 1-60.

Evans, D. E., Surrel, A., Sheehy, M., Stewart, D., and Robinson, L.H. 2008. Comparison of foam quality and the influence of hop a-acids and proteins by five foam analysis methods. Journal of the American Society of Brewing Chemists, 65, 1-10, 10.1094/ASBCJ-2007-1129-01

Evans, D. E., Oberdieck, M., Redd, K.S., and Newman R. 2012. The comparison of the foam stability analysis methods Rudin and NIBEM with a manual pour method to identify beer characteristics that deliver consumers stable beer foam. Journal of the American Society of Brewing Chemists, 70, 70-78, 10.1094/ASBCJ-2011-1205-01

------------------------------
D. Evan Evans
The Tassie Beer Dr
Lindisfarne TAS
61 362439556
------------------------------

Hi Russell 

CO2 and Tetra do not get along so well!!. Did you get the target IBU?

Tetra solubility is highly influenced by CO2. Some of the Tetra you added precipitated due to the producition or addition  of CO2.

------------------------------
Edgar Finol
Mechanical Engineer
Ceveceria Polar CA
Edo Carabobo
+582418162250
------------------------------

Thanks for the help everyone! I think Dr. Evans' photos clearly illustrate the what happened. The Tetra made foam...just before we wanted it to. Presumably it got kicked up when we hit the tank with CO2 to mix up the Biofine. Interestingly, we had some fermcap in there...wonder how those two play together. Ah well, the beer tastes lovely and we have learned yet another What Not To Do.