First Wort Hopping - a possible explanation
By Mark Tumarkin

One of the more interesting brewing techniques of recent years is First Wort Hopping. Actually, it is an old German technique that has been resurrected and gained fairly wide acceptance, at least among gonzo beer geeks. Following is an HBD post that seeks a possible explanation of the mechanism involved.

<editor's note>
The following was taken from the Homebrew Digest.
</editor's note>

------------------------------

Date: Sat, 27 Jul 2002 10:35:22 -0400
From: steve thomas 
Subject: A possible mechanism for first wort hopping


Hello all--
  There is serious contention as to whether first wort hopping (FWH) works,
and I have seen no published reports of why it should work.
  I have made beer with excellent hop flavor where the last hop addition
was over 90 minutes before the end of boil, so I would say there is a real
effect from FWH.
  So how could it work, and why are results so varied?
 The times I have seen the best FWH effect were where the runoff was slow
and the wort was held _just_ below boiling for an extended time.  The
gravity of the first runoff is very high, the successive wort additions
coming just fast enough to suppress an outright boil.  At this level
bubbles form, mostly around the hop petals, rise, and usually disappear
before rising all the way to the surface.
  So what is going on with this program that could optimize FWH?
 A possibility:  High temperature chemical reactions in the gasses in the
bubbles that form and then disappear.
  There are many little appreciated properties of bubbles, amongst them
that they are always under pressure relative to the medium surrounding
them.  Even less apparent is that smaller bubbles are under more pressure
than large ones under the same conditions.  The principle is simple enough
once you stop to think about it: bubbles are bounded by water, the water
applies tension along its surface, the surface being curved applies
pressure inward, the more surface curvature there is per unit area, the
higher the pressure.  This leads to the conclusion that there is a certain
minimum size for a bubble.  At less than the minimum size the surface
tension compresses the bubble contents to a smaller size, being smaller
applies more pressure, being under more pressure grows smaller...until the
bubble disappears.  This property yields all sorts of interesting effects:
carbonation stones work better at small pore sizes because the bubbles more
quickly attain the size where the remaining gas is squeezed into solution;
when wort is first brought to a boil it wants to boil over (it overshoots
the boiling point because the bubbles refuse to form, then the proteins
precipitate forming nucleation points and the solution boils evreywhere at
once), and makes the bubble chambers and cloud chambers beloved to particle
physicists possible.  (The bubble chamber is reputed to been developed by a
guy looking at his glass of beer, looking at that one little stream of
bubbles rising from one point, wondering "hmm, how big would that defect
have to be?")
  Now to apply this knowledge to FWH:  The situation is concentrated wort,
bottom heat, hops, incipient boil.  At the bottom of the pot bubbles form,
rise ,and in rising dissapear.  The bubbles are steam (water vapor), and
volatile fractions of wort and hops.  As the bubble rises from the bottom
it hits the cooler solution overhead and begins to condense.  Condensing at
its surface, the bubble gets smaller, being smaller, its internal pressure
rises.    Things stay pretty well balanced until the bubble shrinks past
the minimum bubble size; then the surface tension effect takes over.  As
the surface tension slams the bubble shut the pressure and temperature
spike, like happens in a diesel engine when the piston squeezes the volume
down.  In that tiny volume of the disappearing bubble is an ideal
environment for chemical reactions between the wort volatiles, hop
volatiles, and steam: gasses at massive pressures and elevated temperatures.
  Under this theory of the mechanism of the FWH effect, a distinct
temperature gradient in the pot, maintained for a period of time, is a key
aspect.  If true, it would go a long way to explaining the varied results
attained, and particularly the nearly uniform lack of success amongst
commercial brewers.  (With steam kettles and lots of power the temperature
gradient will start small and quickly be erased as a rolling boil develops.)

- --Steve Thomas, aka DRSTRANGEBREW



------------------------------

Back to August 2002 front page