Tuesday, July 27, 2010

Optimal Oil Extraction 101.

Whole Cones vs Turkish Espresso Pellets: Where’s That Sweet Spot?

How does a brewer get the most hop oil for the buck? Does he dry hop with whole cones? Or with pellets? The research shows that a brewer using pellets can extract about 30-35% more alpha acid in solution than he can from whole cones, but I’m not aware of any oil extraction studies pitting cones vs pellets.

It’s not a perfect analogy, but assuming the same holds true with respect to oil extraction – that a pellet offers up more oil for extraction than a cone, what is the optimal design of the pellet?

In short, where’s the sweet spot? On one end, we have a properly harvested, dried, baled and stored whole cone flower. On the other, we have that same flower pulverized into a fine Turkish espresso powder compressed to a 3 mm pellet.

How do we open up the flower to best utilize the oil inside the resin glands without unduly exposing them to the ravages of oxygen and heat? And why do we need to “open” them up at all?

The answer to that last question is intuitive. Look at a whole cone. The oil together with the resins is inside the tiny cup- shaped yellowish resin glands. The glands themselves are coated with a permeable membrane, or skin. Even though it seems logical, there’s no definitive research proving that heat or air have an impact on the gland’s permeability. The permeability varies between hop varieties.

The inside of the gland consists of many molecules, including the hop resins, the oil (about 250 bio-chemically distinct compounds) and anti-oxidants (like quercetin and xanthohumol), which themselves help prevent oxidation and prolong the shelf life of both the oil and the resin.

Nature designed the cone to protect those precious glands from predators. They’re tucked around the vertebrae of the cone (the strig) where they cling to the bracteoles, the internal scales shielded by the weather-exposed bracts. If you poured water over the cone, it’s not likely that much would penetrate the bracteoles and reach the resin glands (like water off a duck’s back).

If you dipped the cone into an aqueous solution, more water would reach the central axis, but the process of extracting the oils from the glands is not very efficient. This became clear to me when I recently scooped up a handful of spent whole cones that had been dry hopped. I opened a few up and I could plainly see a few yellowish glands, all perky and plump.

It’s not a great analogy, but think about coffee beans. You can’t dip coffee beans into hot water and efficiently extract any appreciable amount of oil. To bring out the oil, you need to grind the bean up. The question is, to get the best flavor and aroma out of that bean, how do you preserve the bean, when do you grind it up, and how finely do you grind it?

I’ve been applying these same questions to the hop cone. It’s clear to me after examining several pellets from different pellet mills that the size of the pellet and the coarseness/fineness of the grind dramatically influence both the quality and quantity of utilizable oil. Granted, I haven’t measured the “extraction” rate or amount in a laboratory. But it’s fairly well known that hop oils degrade rapidly when they’re exposed to heat, light and air.

If the key to optimal oil extraction is maximal lupulin gland preservation, but the oil glands are tucked inside, how does one “process” the cone, or open it up, and shake out the glands, without unduly rupturing, cooking, or shattering them? I called the People’ Hopmeister , Dr. Al Haunold, for help.

It turns out there is a middle ground, but I’ m not sure how sweet it is. Dr. Al tells me that there was a technique developed years ago for shaking the lupulin glands out of the cone and capturing them fairly whole: pure, concentrated glands containing resins and oils. The shake-out process requires freezing the dried cones followed by a “gentle” shaking. The cones are not compressed into a bale. The process is laborious and both time and space consuming.

The shake-down-and-out method might work in a Willy Wonka-ish factory run by oompa loompahs who never complain. But, after investing a few million in a pellet mill, not sure I’m ready to throw down for a massive shake down operation. Nor do I think there’s an immediate demand for pure unfractionated hop oil, as brewers are accustomed to using pellets and cones, and few have drilled down to knowing precisely which of the several dozen popular oil “essences” they want for each brew style.

Al explains that the resin glands during picking and drying tend to fall out of the tossed-about cone. The rate at which the glands fall or shake out depends on the variety, the moisture content, and the harvest date – if the cone is harvested late and is therefore too “fluffy,” then the glands are more likely to fall out – a phenomenon he calls “shattering.”

A badly harvested, picked and dried cone can lose up to 40% of its lupulin glands. Where do they go? They fall on the floor. Per Al, you can separate the good farmers from the mediocre or worse by the concentration of yellow lupulin glands on the picking and drying floors – the so-called “Yellow Floor” syndrome. And by the way, according to the Hop Oracle, it’s not unusual for the farmer to scoop up all that yellow gold and sell it separately to extractors in years of hop shortages. In good hop production years, there may not be much of a demand for such sweepings.

All that piney, citrusy, mango-ish, floral oil, together with all the bittersweet alpha, swept away like dust in the wind. A tragedy!

So, where do we go from here? We continue to question and tinker. I recently met with a brewer who said he wanted to experiment with dry hopping using both pellets and whole cones. He’s convinced that while traditional, and perhaps even romantic, dry hopping with whole cones leaves a lot of juice on the table (in addition to soaking up a lot of valuable beer). He wants to dry hopping using cones, in one batch, hand, and coarsely ground and fatter IH pellets, in another, and evaluate the differences.

Straight up he says whats driving his curiosity is a blend of both wanting to up the quality of his brew and save money by using fewer hops but extracting more flavorful oil. We like that. Question everything.

In the meantime, we control the things we can. For example, we will freeze our freshly harvested 2010 bales on receipt. We’ll hammer the flowers minimally and squeeze them through our die lovingly at under 110 Degrees F. And we’ll double nitrogen flush our cool pellets, wrap them in an impermeable layer of foil, and whisk them right back into the deep freeze in under 70 minutes. Can’t wait to crank it up!

Roger Worthington

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