Hop Utilization, Prepping a Barrel & Yeast Washing: Mr. Wizard

I use a hop spider to reduce the amount of debris in my chilled wort prior to transferring it into my carboy for fermentation. The hop spider is a 5-gallon (19-L) paint netting attached to a 3-inch (7.6-cm) PVC pipe and suspended into the kettle by legs. The hop pellets mostly stay in the bag rather than roll in the boil.
Is there less hop utilization for the pellets in the hop spider? What about the hops at hot break? Do they impart less aroma/bitterness than hops free floating in the final whirlpool?
Michael Florez
Cincinnati, Ohio

The name hop spider is peculiar to me since these devices don’t resemble any spider I have ever seen! But they are effective in retaining hops and minimizing carryover of hop debris after the boil. They can also reduce wort loss for brewers who stop wort transfer when debris is seen in the line to the fermenter. So in general, I think hop spiders make sense and are a very useful tool for the homebrewer.

Your question is primarily about hop utilization. The primary factors that influence hop utilization are boil time, wort density, and wort pH. Secondary variables include hop type (pellet versus cone), kettle geometry, kettle size, and contact between hops and wort. The latter is the variable of concern with hop spiders. If hops are not able to fully hydrate and/or have limited contact with wort, then a reduction in utilization is likely to occur. This is pretty easy to address by simply making the netting large and non-restrictive, which it sounds like is not a problem in your case. In a crude sense you could line your kettle with a grain bag that could be removed after the boil to lift all of the hops out of the kettle similar to the inner portion of a lobster pot.
I don’t know how hops that end up in the trub pile in a whirlpool differ in their contribution of aroma and bitterness compared to hops that may be floating around in the whirlpool. In commercial brewing operations, even relatively small ones, pellet hops intended for late hop character are added to the kettle at the end of the boil and the wort is either pumped to a separate whirlpool vessel or it is pumped back into the kettle to cause the wort to swirl. Following this step the wort is allowed to rest for about 20 minutes. This rest period is long enough for wort movement to effectively stop and for the trub pile to form, and the total time from hop addition to the beginning of wort cooling is at least 30 minutes, usually closer to 40 minutes. This is ample time for aroma extraction and my guess is that hop aroma would not differ if an experimental beer were brewed with the same contact time with the aroma hops and no whirlpooling, and hence less hops in the trub pile.

There is a very real practical consideration with this question, however, and that has to do with the contribution of bitterness with aroma hop additions. Back in the days before ultra-hoppy beers many brewers, both homebrewers and commercial brewers, either ignored the contribution of bitterness of late hop additions or assigned a fairly low utilization rate for the addition. This made sense for most beers where the last addition was typically less than or equal to the other hop additions. A mistake in the assumed utilization was not a big deal because the last addition was not large enough to contribute much bitterness.

The truth is that aroma additions can significantly contribute to bitterness because the utilization of this addition can be much higher than assumed when pellet hops are used. Just check out some of the current tables about hop utilization and you will find that almost all of these tables relate utilization to boiling time, where late hop additions typically have predicted hop utilization rates around 5% based on a few minutes of boiling. The problem with this is that most of these tables show the utilization to be 0% with no wort boiling. While this is true of dry hopping, it is not true when hops are added to hot wort, as is the case with hops added at the end of the boil and hops added to the whirlpool.

My guess is that this mindset began before hop pellets became so prominent in the world of brewing. Some breweries still add pretty large, sometimes massive, late hop additions to the kettle using cone hops and almost immediately transfer the wort to a whirlpool or hot wort tank. During the transfer the cone hops are removed and the contact time with hot wort is greatly minimized. Instead of being in contact with hot wort for 20 minutes during transfer to the whirlpool, followed by a 20 minute whirlpool rest followed by up to 60 minutes during transfer to the fermenter (these are typical commercial brewery times) the contact time is about 20 minutes; a full 80 minutes less. This is a very significant difference as the utilization associated with the late hop addition increases from somewhere around 5% up to about 20%, depending on wort gravity and contact time with hot wort. Add this threefold difference in utilization to the sometimes incredible increase in late hop addition rates and the result is beers with a lot of bitterness directly related to late hop additions.
The cool thing about the hop spider is better control over your bitterness, if you are so inclined to want to nerd out! I am that sort of brewer who likes knowing how my beer is affected by what is done in the brewery. With the hop spider you can make those massive late hop additions, using pellets or cones, extract the aroma from the hops and pull the hops out from the wort before contributing bitterness that is not so easy to calculate. Hop on Spider Man!

I just received an 8-gallon (30-L) bourbon barrel, but I realized I don’t know what I need to do to prepare the barrel. My beer won’t be ready for 30 days, and the barrel “has been freshly emptied,” according to the supplier i bought it from. Is there anything I need to do to the barrel in the meantime or can I just siphon the beer into it when it’s ready?
Bill Bartman
Portland, Oregon

Bourbon barrels can be used to produce some really great beers. At Springfield Brewing Company, like many craft breweries, we use bourbon barrels for some of our beers. Our anniversary beer for the last few years has been a fruited stout partially aged in bourbon barrels and our Little Barrel of Nectar is a stout we produce when the stars are aligned using 8-gallon (30-L) bourbon barrels from Woodinville Whiskey. And most recently we aged our Tsarry Night, a Russian imperial stout, in rum barrels to produce Arrghy Night.

So my answer below will come from my experience with these beers.

When we purchase freshly emptied barrels they arrive with the bung in place and sometimes wrapped in plastic. We leave these barrels alone until we are ready to use them because nothing good comes from opening these barrels to smell them and “ooh” and “ah” about what will be. Patience is required when you have the barrel in your possession but no beer to put into the barrel.

Let’s talk about the beer for a moment. Beers that are destined for bourbon barrel aging need to have enough girth to carry the flavor intensity of the bourbon. You can surely make a great bourbon beer that is not a monster, but you may need to blend the barrel-aged component in order to achieve a beer with balance. Many brewers have followed the lead of the tinkerers of this style of beer and have chosen big stouts to put into bourbon barrels. This works for a number of reasons, including the compatible flavor hooks between stout and bourbon barrels, similar flavor intensities, and the way strong beers respond to oxidation. I want to hit on these points one by one.

Bourbon barrels may seem rough and gruff on the surface, but they do have lots of nuance. If you are lucky you will have coconut, vanilla and caramel notes from the bourbon barrel marry with the flavor notes of your base beer. This is why, in my opinion, stouts work so well for bourbon beers. Matching the intensity of the beer with the intensity of the barrel is also something to consider. Since bourbon barrels have a loud and dominant voice they can easily overpower the whispers of subtle ales, such as brown ale. This is where blending can be used to temper the boisterous barrel flavor if you desire something more subtle. And then there is oxidation. Barrels are porous and beer aged in wood is exposed to oxygen. So choosing a style that benefits from slight oxidation is something that I strongly suggest until you have a few of these brews under your belt. Chances are you will find that this is the best type of beer to age in your bourbon barrel.

Let’s go back to the barrel. When your brew is finished it is very important that you do nothing to increase the level of carbon dioxide. If you want to chill your brew to drop yeast, do it in an atmospherically vented container like a carboy or a conical fermenter that is not pressurized. To prep your barrel, all you need to do is remove the bung, pour out and reserve any bourbon that resides in the barrel and rack your beer into it. This is where homebrewing and commercial brewing diverge. If you want to leave this bourbon in the barrel there is nothing stopping you. The commercial world brings in tax compliance rules that are involved and, luckily, out of the scope of your question. Most beer aged in freshly emptied barrels will have extracted most of the bourbon notes in about 3 weeks. From this point forward you should treat this beer no differently than green, still beer following primary fermentation except that you will need to add yeast if you plan on bottle conditioning.

Rewind the tape, if you will for a moment. Not all barrels are freshly emptied. Some were used for aging bourbon (or some other variant of whiskey, wine, or spirit) and permitted to dry out a bit. And others were used to age beer once before. What is a brewer to do?

If you have a dry barrel you need to be concerned about leaks and will want to fill the barrel with very hot water to help the wood hydrate, swell and seal. Dry barrels also lack the residual bourbon of wet barrels and the bourbon is pretty darn important when it comes to imparting bourbon flavor. At home you can hydrate your dry barrel and fill that wooden sponge back up with bourbon. Just buy a good bottle of the brown stuff, pour into your hydrated barrel, hammer in a bung and roll the barrel for several days to let the wood soak up the bourbon. You should pour out the excess to prevent overwhelming the beer.

And if you have a barrel that has been used once for beer you probably can use it again and extract more bourbon flavor without any help from a bottle (as described above). This is a good time to barrel age a tamer beer. Or you can use this second run from the barrel to blend with the first run. Barrel aging is not rocket science. It works very well for certain beers and you will produce a great beer if you stick to the fundamentals!

I have always wondered about the desire of many brewers to yeast wash. It seems to me that if you are trying to save yeast that you should simply make more yeast starter than you need and save the excess starter for the next batch. This seems easier and more likely to maintain the integrity of the strain. What am I missing?
Michael Miller
Poway, California

I too question the desire of many brewers to acid wash their yeast. But before diving into why yeast washing is used I want to touch on another topic raised in your question. The idea of growing a large starter, using what is needed for today’s brew and saving the remainder is an appealing idea. The problem with doing this, however, is that the viability of a yeast slurry declines over time and it is really advisable to use fresh slurry within one to two weeks following propagation, assuming that the slurry is stored right around 32 °F
(0 °C). Most commercial breweries with a yeast propagation program would rather not use yeast that is stored more than a few days. The bottom line is that when yeast viability drops during storage the likelihood of fermentation problems increases.

And this is why most breweries harvest yeast from a batch that just completed primary fermentation, store the yeast for as short a time period as possible and pitch it into a fresh batch of wort. It is this method that can benefit from washing. Since yeast from a previous fermentation can become contaminated with bacteria and wild yeast, the practice of re-pitching can be problematic. I think this problem is not as common today as in the past because of improvements in process control, especially tank cooling, process technology, specifically closed fermentation vessels and hygienically designed pipe and valve systems and overall improvements in cleaning methods. But not all breweries have the latest and greatest technology, especially older ones. So yeast washing is alive and well today.

Yeast washers come in two basic camps. One camp sees yeast washing as something that can be done in a pinch. These brewers monitor yeast and beer in microbiological labs looking for potential problems and/or simply wash after a certain number of generations that coincides with problems (this is brewery specific and requires sufficient data to establish a routine that makes sense). If they pick up certain bacteria (usually lactics are the beasts of interest) on their test media and really need to use the yeast related to the sample, acid washing can be used as a form of chemotherapy to reduce the lactic acid bacteria population without harming the yeast too much.

Make no mistake, reducing the pH of yeast slurry to 2.2 to 2.4 and holding it for about two hours is not super friendly on the yeast. If the temperature warms up above about 40 °F (4 °C), the pH is errantly lower than 2.2 or the time extended beyond two hours, damage will occur more than the method already permits.

There are other washing methods used that are not as harsh, but the phosphoric acid method is still common among brewers who like to acid wash. Chlorine dioxide is a much gentler washing solution, has gained popularity in recent years and is equally, if not more, effective in reducing bacterial populations than phosphoric acid (note that these methods are not effective at reducing the population of wild yeast strains).
The other camp always acid washes yeast after cropping. These brewers have a pragmatic and fairly logical thought process. Since it takes time to determine if there is a problem, always acid washing cuts out the lab time that may simply indicate that a problem exits. Washing the yeast every time is a way of being safe rather than sorry. The other part of this camp’s philosophy is that acid washing and chlorine dioxide washing reduces yeast viability, and reduced viability will change the way yeast behaves compared to yeast that has not been acid washed, so in order to have predictable yeast and predictable fermentation performances the yeast should always be acid washed.

This is a pretty big topic and I only scratched the surface. Yeast can also be water washed, although I don’t know of any breweries still practicing this method. Yeast can also be harvested and passed through a tight screen to remove trub. And there are as many ideas on how and when to crop yeast from the fermenter as methods to screen, store and wash. Most craft brewers that I communicate with crop, store and re-pitch without any screening or washing steps. I hope this gives some insight into your question.

Issue: May-June 2015