Fermentation Under Pressure, A Solera System, A New Flavor in a Classic Beer, and Cooking Beer

Q I recently purchased the 27-L (7.1-gallon) FermZilla conical fermenter. I just completed my first attempt at pressure fermentation. I read several articles about how fast and convenient it can be, as well as a great way to keep the batch of beer away from oxygen during transfers. I waited 24–30 hours before setting my spunding valve to 12 psi. Fermentation was very active and I had a fair amount of kräusen with a relatively steady temperature of 72 °F (22 °C). After about a week, I could still see what I believed to be continued fermentation. The specific gravity had dropped from 1.066 to 1.018, but it still looked like active fermentation and there was still kräusen on top. It also didn’t really clear much during the second week in the fermenter, but it is a witbier. Is a steady specific gravity the best way to determine when primary fermentation is over? Should I always go by specific gravity with pressure fermentation?

John Collins
Gaffney, South Carolina

A Yes, using gravity to monitor fermentation status is the best method for use at home because observing bubble activity and kräusen appearance are simply not reliable indicators. I am a fan of clear fermenters (like a carboy or FermZilla) because visual observation of movement during fermentation is telling, but that convenience is given up when using stainless steel. Commercial breweries almost exclusively use closed, stainless steel fermenters these days and monitoring activity using instruments is the method in the commercial world of brewing. When monitoring fermentation using density measurement, the end is typically marked by steady readings over 2–3 days. That usually works, until it doesn’t.

Whether fermenting in glass or stainless, and under pressure or not, fermentations sometimes fail to fully attenuate. It’s always a good practice to have an idea of where a fermentation is likely to finish. This depends on grist bill, original gravity (OG), and yeast strain. For the sake of discussion, let’s assume a witbier has an apparent degree of attenuation of 78%. In your case, predicted FG = [66 – (66 x 0.78)] = 14.52 (gravity points) or 1.015 (specific gravity). Your beer finished at 1.018. If you have multiple data points at 1.018, it’s reasonable to conclude that your fermentation finished a bit higher than expected or that your fermentation may be stalled/stuck. Unless you run a forced fermentation (small, over-pitched, fast ferment used to identify the finish line) alongside of your large fermentation, you really don’t know if you are finished or not. Because 1.018 is not much over my estimated FG of 1.015, I would consider this fermentation complete and chalk up the difference to something to do with mashing.

When monitoring fermentation using density measurement, the end is typically marked by steady readings over 2–3 days.

Let’s take this example to an extreme . . . instead of finishing at 1.018, what if the fermentation was sitting at 1.022? Without having any forced fermentation data, my brewing experience is telling me that there is a pretty high likelihood that this fermentation has stalled and is stuck with fermentables still present. Again, this can happen in any type of fermenter and at any over-pressure. The kräusening method is a great tool to have in one’s bag of tricks to address suspected stuck ferments. Simply add very young beer, aka kräusen beer in the high-kräusen stage of fermentation, at a rate of about 10% of the batch volume. Stuck ferments are usually jump-started by the addition of kräusen beer and will finish out fairly quickly. This is an especially effective tool for bigger beers.

Another layer to this onion are changes in turbidity as fermentation moves through the process from wort to beer. Beers like weizens, wits, and hazy IPAs are not the best types to monitor using clarity as a metric tied to finished beer because these styles are all cloudy to varying degrees. Suffice to say, assuming that cloudy styles will go from one degree of cloudiness to a lesser degree of cloudiness is probably realistic because yeast is not the main source of haze in these beers and some clearing is likely to occur at the end of fermentation, but using cloudiness as a performance metric is a pretty dull tool.

Gravity is much more revealing . . . but it does consume beer in the process. That’s one reason in favor of extending the time at fermentation temperature for ~3–5 days after the end of obvious activity before pulling a sample for measurement. I am a pretty frugal homebrewer and am not keen on sacrificing more beer to Ninkasi than required (sorry Ninkasi, goddess of brewing and the baker of the bappir). If I am expecting a FG of 1.015 and measure something near it 3–5 days after the party seemed to end, I am OK with chilling and moving to the next step.

You also mentioned observing kräusen on the top of your fermenter towards the end of the period associated with active fermentation. That’s not uncommon, especially with top-cropping yeast, like many witbier strains.

And now onto the last major layer to your question: Carbon dioxide release and spunding valve set point. When beer is fermented under pressure, carbon dioxide will saturate the beer at the temperature-pressure condition of your fermenter. You fermented at 12 psi and 72 °F (22 °C); beer equilibrated with carbon dioxide under this condition contains about 1.48 volumes of carbon dioxide. That is pretty low in carbon dioxide, so much so that most folks would describe this level of carbonation as “flat.”

spunding valve on a Corny keg
Applying a spunding valve during fermentation has become a popular technique in homebrewing over recent years, but a lot of questions still surround the concept. Photo by Christian Lavender

Because you are spunding early in fermentation, it’s safe to assume that you are totally equilibrated after a couple days of gas venting. The only reasons for gas venting late in the process are continued fermentation and gas production or increases in beer temperature that will reduce the solubility of carbon dioxide, increase keg pressure, and cause gas release for your relief valve. You may have been observing the effects of slowly fermenting beer.

Pressure fermentations are convenient for a few reasons, including possible changes in ester profile, fermentation rate, and, the big one in my view, carbonated beer at the end of the process. In order to end up with fully carbonated witbier at 72 °F (22 °C), an equilibrium pressure of ~36 psi is needed (note the FermZilla is rated to 34.8 psi). While that pressure is too high for primary fermentation, it is required if you want to end up with fully carbonated beer. The next time you ferment under pressure, you should consider increasing your spunding valve setting with at least 1.5 °Plato residual extract (1.5 °P / 1.006 above predicted FG) to ensure you have enough fermentables to end up with fully carbonated beer. Hope this information is helpful.

Q Can I do a solera project in a 10-gallon (38-L) barrel without bugs or am I missing the point?

Mike Biel
Kenosha, Wisconsin

A Quick definition for our readers: The solera process is a type of fractional blending used to produce a diverse range of aged liquids including Sherry, vinegar, wine, whiskey, and beer. The term solera comes from solum, loosely meaning “ground” or “bedrock.” The solera system consists of multiple layers of barrels called criaderas, with each layer representing a blend component, usually a harvest year of the final blend that happens in the bottom layer of barrels. Because the barrels are at the lowest level, i.e., the ground level, of the system, they are called soleras. Etymology aside, there is absolutely nothing in the rulebook that states that your solera project must include bugs, bacteria, or funky yeast related to how some sour beer brewers operate their solera systems.

According to the books, the main reason that this system was originally developed was to improve the consistency of Sherry. By definition, Sherry must be aged for at least three years. As such, a common method for Sherry production is to annually transfer about a third of each barrel in the system. This transfer process begins at the bottom by bottling a portion of the solera and replacing by re-filling the solera with the criadera one tier up, then refilling that criadera from a level up, until the top criadera is then filled with new product.

The other rule related to your question is the number of layers and the number of barrels: No rule exists! You can indeed use the solera process using a single barrel so that every year you have a bottling of one-year product blended over the age of your solera. In practice, it does make sense to do something other than aging beer in a solera system (or single-barrel solera) because the oak characters are going to quickly fade as the solera is used for multiple bottlings. You could move aged beer into a new barrel, but if your solera system consists of only one barrel this process would put in a kink in the whole consistency idea. Whatever the master plan, the solera system is a pretty nifty method with lots of fun and interesting applications — no bugs required!

Q I have a question related to a persistent flavor that I first noticed in my favorite American major domestic lager about a year ago. I find the same flavor in other beers brewed by the same company. Not sure exactly how to describe the flavor but it reminds me of the type of straw used as bedding in a barn with a bit of earthiness added into the mix. Does this make any sense? If so, what could be contributing this flavor?

Joe Chapman
Little Rock, Arkansas

A Thanks for the interesting question, Joe. I also enjoy all types of beer, so I went to the store and purchased a selection of beers in attempt to put a finger on what you are describing. It sounds like you are describing grain flavors that are either new to your favorite beer or new to you.

My own taste panel consisting of me, myself, and I, did note a grainy/grassy note in several beers by one of the major U.S. breweries; Brewery Z or BZ for sake of discussion. In my statistically insignificant, but otherwise enlightening sensory exercise, the grainy/grassy notes in beers from BZ were much easier to detect when tasted against other beers. This sort of tasting requires a solid palate, keen attention to detail, and the persistence of a mule. Because of the solitary approach to my analysis, I repeated the sampling a few times (I did buy 6-packs after all) so that I was convinced that my palate was not the issue. My conclusion is that beers from BZ have a pronounced grain/grassy note. But as I mentioned, this observation has zero statistical validity.

This flavor, it’s real and not somehow related to bias, is probably from the grain because these beers don’t have too many ingredients that could contribute such flavors. How’s that for being obvious? I don’t know if this character is a new character for BZ because, up until reading your question, I had not previously tasted several domestics at one time and had not noticed this pattern with BZ.

What I do know is that not all base malts taste the same. These differences may be due to differences among malt houses, barley sources (growing region), growing year (weather effects), barley variety (genetic effects), and how the malt is produced/kilned (process effects). Differences among malts is one of the many things that makes brewing interesting. It’s very easy to make malt teas to assess the aroma and flavor of malt before brewing. Just like with hop evaluations, much of the aroma found in malt does not survive wort boiling and some of the more volatile and overt notes are removed with water vapor. One of the keys to raw material sensory is knowing what may make its way into finished beer. So all of these observations need to be taken, at least to some degree, with a grain, er, kernel of malt.

But there is something else that may be going on here. As people age, our senses change. Unfortunately, this change is usually accompanied by a decreased sensitivity to subtle notes. It’s possible that your perception of your go-to beers is changing, rather than the beers themselves changing. Another possibility is that you are recovering from something like COVID-19 that temporarily whacked out your senses. What once tasted clean and crisp is now being perceived as grassy and green. Now I am questioning my own palate!

Not sure what else to write about this. Perception can be a transient thing as can flavor profiles of beers we may know very well. Breweries generally avoid making changes to beer that can be detected by consumers, but sometimes changes are abrupt and are detectable. If you don’t like the change, my suggestion is to find a new commercial fave for those times you are low on your own brew. In the meantime, pick up the pace and brew your own!

Q In an article by John Naleszkiewicz in the October 1995 issue of BYO, he reviewed a method of removing the alcohol after fermentation by heating the beer in an oven at 180 °F (82 °C). Is there any risk of fire with this method?

Chris Patterson
Downers Grove, Illinois

A Wow! Talk about a blast from the past and a reminder of how brewing trends often slowly develop. The topic of no-alcohol and low-alcohol beers is certainly gaining traction in the world of craft beer as consumer trends are pulling breweries in new directions. Depending on the conditions, enough alcohol vapor could conceivably accumulate in an oven containing a pot of beer to create a combustible atmosphere, but it’s pretty unlikely.

A much more likely scenario, however, is really gnarly beer remaining in the oven following this process. Even if an oven-based process was designed to eliminate oxygen from the beer, the beer would certainly develop cooked flavors because batch distillation like this requires long exposure to heat. In the September 2022 issue of BYO, I covered several methods currently used to produce low-alcohol and no-alcohol beers. The “Advanced Brewing” column in the October 2022 issue also covers the topic. I recommend giving those both a read.

My usual view on homebrewing methods is to go with the flow and embrace the free-spirited innovators who make homebrewing so vibrant. In this case, however, I suggest more nuanced methods to the pursuit of low/no-alcohol brews than the oven treatment.

Issue: November 2022