|If you love hoppy IPAs like I do then you'll be interested in lupin. Lupulin is small glands that contain hop acids
and essential oils.They are observable as a fine yellow powder found deep within the hop cone—a fruiting body,
which is technically called a strobile. The cone is made up of bracts and bracteoles that are attached to a central
rachis (or strig). The lupulin glands are found attached to the base of the bracteoles and to a lesser degree to
the bracts. They are small, slightly pear-shaped glands roughly 0.2 mm in diameter.
Their concentration in hops differs from one variety to another. Given that most of the brewing value of the hop
cone is found within the lupulin glands, there have been a number of technical approaches to concentrating or
preserving this component. A process for washing hop cones of their lupulin with water followed by sieving,
drying, and storage in an inert environment has been developed and patented.
Type 45 hops are a pelletized product whereby the hops are milled and then sieved in order to concentrate the
lupulin. In this process, 220 lb of whole hops yields roughly 99 lb of concentrated hop pellets, hence the name.
Supercritical CO2, liquid CO2, and ethanol extraction of hops are techniques for dissolving lupulin, removing it
from the hop cones, and recovering it as a solvent-free (in the case of CO2) or ethanol-based extract.
That alpha acids are the principal components in lupulin, Chemically, alpha acids reside in the soft-resin fraction of
the lupulin. They are expressed as a percentage of the total weight of the hop and exist as complex hexagonal
molecules. Alpha acid analogues include humulone, cohumulone, and adhumulone, which, when isomerized to
isohumulones (iso-alpha acids) through the boiling process, bring bitterness to beer.
There is some debate among experts as to which of the humulones gives the cleanest bitterness. There seems
to be agreement, however, that high levels of cohumulone are an indicator for potentially harsh bitterness.
Cohumulone levels are listed on a hop analysis, usually right next to the alpha acid percentage.
When dissolved in beer as iso-alpha acids, the unit of measurement for bitterness is International Bitterness
Units of IBUs. The hops’ alpha acid value is then used by the brewer to formulate a recipe for the beer’s final
bitterness. Brewers adjust hopping rates based primarily on the selected hop’s alpha acid content expressed
as a percentage of the hop’s weight. Because the kettle process is inherently less efficient at extracting
isomerized alpha acids from hops than a laboratory process can be, the brewhouse utilization rate rarely
exceeds 30%. When more than one hop variety is used, the contribution of each variety to the beer’s final
bitterness is calculated separately and then added up.
Hop alpha acid levels are highest at the point of harvest and diminish gradually and continuously during storage
because of oxidation. Refrigerating or even freezing hops after they have been harvested and kiln dried helps to
delay oxidation and preserve their alpha acids longer. Hops that have been processed into pellets or into
concentrated hop extracts, on the other hand, tend to maintain their alpha acid levels better.
“Skimming" is a term referring to the removal of a substance from the surface of a fermentation, usually one
taking place in an open vessel. For lager fermentations, skimming usually refers to the removal of proteinaceous
cold break material that floats to the top of the wort soon after it is cooled into the fermenter. This material, which
is brown and granular in appearance, is felt by some brewers to be detrimental to beer flavor.
Others prefer to leave it intact, citing evidence that it contains nutrients that promote healthy fermentation. Once
high krausen is underway, another residue may eventually form on top of the foam. Called brandhefe by German
brewers, this may also be skimmed because it contains hop resins that may coarsen the beer’s bitterness.
In traditional British ale brewing, skimming refers to the recovery of brewing yeast toward the end of fermentation
in a fermenting vessel where a “top cropping yeast” is used. Yeast is normally skimmed from relatively shallow
square or round fermenters. Yeast is not skimmed from tall cylindroconical fermenters; yeasts in such tanks will
usually sediment to the bottom of the vessels. When a beer is fermented using a top cropping yeast strain, the
yeast will separate out from the body of the fermentation and rise to the beer surface. This will happen when most
of the nutrients have been used up, so the yeast has no reason to stay in the wort; it will therefore flocculate
(combine together in clumps) and form a thick, creamy yeast head on the beer.
The most common method of removing this is to suck the yeast off the vessel using a vacuum pipe attached to a
tray that is floating on the surface of the beer; a special skimmer or paddle is used to pull the yeast into the tray
and vacuum pipe.The yeast skimmed from a vessel may be collected and stored for use in following fermentations,
with the excess often sold another brewery, a distillery, or as a by-product for animal feed
Hope you found this month's column of interest. If you have any questions about beer or brewing
or just want to submit a word for me to discuss here just e-mail it to me.
Thanks and Cheers!
|Lupin // Skimming
|A new column by
|Jack O'Reilly attended the
famous Siebel Institute/ World
Brewing Academy in Chicago.
|I'm very excited to be part of the BeerNexus team. I think my many years in the
beer business both as a brewer and manger will enable me to explain and
investigate many topics of interest for those who really love craft beer. Hope you
join me every month.
More by Jack: #1, #2, #3, #4, #5, #6, #7, #8, #9