Hop Processing - Quality Control - Myrcene

After testing hops for six years I have seen a few trends in the data.  Early on I wondered what contributed to low oil in hops?  After conducting numerous studies looking at drying temperature, harvest timing, and pelletizing, one thing  became incredibly clear.  Temperature plays the most significant role in quality, and the levels of myrcene is your "canary in the coal mine" when it comes to evaluating hop processing quality.

It's true, low oil (and low myrcene) in hops can be from an early harvest.  Yet we learned that if a hop was harvested early it will have a cohumulone value below the varietal range.  So, we now know if low oil is harvest timing or processing issue.  

In the past there wasn't a focus on dry-hopping, dipping, late additions, etc.  Compounds like myrcene were thought to be simply "boiled off" by classical hop additions, so processors moved to throughput, increased temperatures, and the losses in quality were accepted.  

Well, times have changed, and for awhile now......brewers want intense aromatics.  But how do we preserve the aroma?  Well, modern hop processing is low temperature, nitrogen purged, enclosed equipment.  If your kiln smells great and fills the barn with hoppy goodness, your losing oil,  and boiling off dozens of compounds.  

We need to have a basis of quality, a starting point for aroma - Aroma Quality (AQ).  While I’m not suggesting all hops are identical in the essential oil composition, what I am suggesting is that the most historically monitored 7 compounds used in our (AQ) test profile are the same for all hops of the same variety.  This is genetics at work.
The 7 compounds used in or (AQ) test represents the bulk of the oil in hops.
Of these compounds, myrcene makes up 20-70% of the total oil in hops.  Why is this significant?  The most popular varieties growing today are high in myrcene and used extensively for aroma/dry hopping.  In addition, myrcene is known as the mother of all terpenes, it is the base molecule for many aromatic compounds and most likely plays a significant role in dry hopping and “biotransformation”.


Myrcene Content (as a % of total oil)
Citra® - 60-65%
Centennial – 55-65%
Mosaic® - 47-53%
Simcoe®-  45-55%
Strata® - 52-65%
Talus™ - 40-50%
Zappa™ 60-70%
Necaron® - 55-65%
Cascade – 50-60%

With this in mind we need to treat myrcene as the “canary in the coal mine”
Why?  Because myrcene is not only the largest fraction of hop essential oil, but it is also one of the most volatile. 

What does it mean to be volatile? 

When you smell hops, most times at room temperature, you are inhaling the most “volatile” compounds.  These compounds are basically boiling or volatilizing into the air and into your nose.  While myrcene makes up the bulk of these volatile compounds, there are dozens of other compounds (mostly esters), that are also very volatile.

Esters=Fruit  The same esters we have analyzed in hops, are the same compounds used in the flavor industry to add fruit flavors to drinks, food, candy

When drying hops, temperature is critical; the lowest possible temperature to get the water content to 8-12% is desirable.  Why?  Because any elevated temperatures >~110F will “volatilize” these compounds.  Higher drying temperatures will cause significant losses of myrcene/pinene/esters.

How do we know this?  We’ve conducted multiple drying & pelletizing studies where the results proved that this is what happens to hop essential oil composition at elevated drying & die temperatures.  Significant losses of the most volatile essential oil compounds.

So, at elevated temperatures you will not only lose significant total essential oil, but you will lose the most volatile monoterpenes -  myrcene/pinene & esters .  With some samples we’ve analyzed, all of these compounds have been lost due to heat during processing.  

By monitoring the myrcene – “canary in the coal mine” - we can effectively evaluate the impact to all the dozens of other critical compounds that are lost with it.

Beers that are brewed with hops that have lost their myrcene typically have a taste profile with none of the front end bright flowery or fruity notes & aromas, they have a herbal body, and an earthy finish.
Why?  This is because you’ve lost those compounds in processing.  What’s left behind are the sesquiterpenes – humulene, caryophyllene, farnesene – these are much less volatile, and this is the flavor profile of these oils.

How do we know this is what happens in beer?  With SPME & GCMS we have analyzed many dry hopped and traditionally hopped beers and found that almost all the same compounds that we test for in hops are found in  beer.  So, if your hops don’t contain these oils, they are not going to somehow show up in the beer or its flavor profile.

So, how can we protect the myrcene content in our hops?  How can we meet the varietal specs for (AQ)?
Test your processes.  We know what the AQ should be for every variety, just test after drying, and then after pelletizing to evaluate your losses.

Cheers,
Zach