Rehydrating Dry Yeast, Bottle Bombs & Fading Hops: Mr. Wizard

Being new to homebrewing, I am reading as many books and magazines as I can, reviewing sites like and poring over the message boards. The rehydrate/don’t rehydrate dried yeast debate has got me confused. So far I’ve only used SafAle US-05 and pitched it dry in the wort for both of my batches. The beer was good in the first batch, and the jury is still out on the second since it’s still fermenting. Is there a final verdict you can offer me? Or should I just start strictly using liquid yeast? I prefer hoppy IPAs and beers with a good hop character and plan to brew those exclusively very soon.
Justin Cooke
Yuma, Arizona

It has been a while since I have used dried yeast and did a little reading before answering this question. All good references I found on this topic did not leave any doubt in my mind about what is best for the yeast cell, and that is to rehydrate dried yeast with water prior to pitching into wort (or must for any winemakers out there in the audience).

The basic reason behind this practice is that cell membranes serve a variety of important functions for the cell and these functions all require membranes that are fluid. And when dried yeast cells are hydrated in a
liquid other than water, like brewer’s wort, there is a short timeframe when compounds that ordinarily do not pass across the cell wall do indeed cross the cell wall. This leads to a reduction in cell viability in comparison to yeast that has been hydrated in warm water. While the optimum rehydration temperature seems to be strain-dependent, the range cited is usually 95–105 °F (35–41 °C). As the rehydration temperature decreases, viability following rehydration also decreases; rehydrating in water warmer than 105 °F (41 °C) also decreases viability.

The likely cause for this on-going debate is that rehydrating in wort does not result in total failure. So the argument follows that rehydrating in wort works, therefore arguments about rehydration in water and improved viability are simply textbook. In practice, commercial breweries place yeast viability and vitality towards the top of yeast topics that clearly influence beer quality. I believe in the “put your money where your mouth is” gauge. Based on what is said and done vis-à-vis equipment investments in pursuit of yeast viability and vitality, the logical con-clusion is that this is indeed a worthwhile pursuit.

My recommendation to new homebrewers is to add different techniques as the basics are mastered and when new and more advanced brewing methods are an avenue to either better beer or something of practical interest. I certainly would not suggest jumping from dried yeast to liquid yeast simply because there are two arguments about yeast hydration. You can certainly brew excellent tasting beer using dried yeast and the basic science suggests that hydrating in warm water prior to pitching is the best way to handle this type of yeast.

I have been bottling in bombers for three years without issues. Following my normal process I have had four detonations and everything has been a foam fountain for my last three batches. What could have changed to cause this?
Mark Conner
Vancouver, Washington

Bottle bombs are really scary because glass shrapnel can cause severe injuries. The first question that always comes to my mind when hearing about this problem is “how old is your glass?” Some brewers re-use bottles over and over again and eventually the bottles begin to fatigue and fail. Breweries using returnable glass bottles have glass inspection systems to help spot glass with fractures and remove suspect bottles prior to filling. However, I don’t think this is your problem because of the foam fountains you mention.

If you were a new brewer I would suggest that you get control of your bottle conditioning, but my gut tells me that you have bottle conditioning figured out and you are not simply adding too much priming sugar. I think your problem is with super-attenuation. This happens when something in your bottle is able to convert unfermentable dextrins into fermentable sugars. And the most common critter that causes this to occur is Brettanomyces. Considered a wild yeast by most breweries, Brettanomyces, or simply Brett, is increasingly being welcomed through the front door of many a brewery.

The problem with Brett is that this yeast is hard to kill and is a whole lot like garlic, in that a little bit goes a very long way! A few viable Brett cells in a beer bottle will slowly find food from sources unusable by “normal” yeast. Over time, Brett will cause bottles to become highly carbonated and turn them into the occasional grenade. I personally like Brett when I want certain aromas and flavors. But when unwelcome, this yeast is a real problem and I have a hunch that this may be the source of your problems.

If you have not been dabbling with Brett, I suggest verifying that the beers you package are indeed done fermenting prior to packaging (research “forced fermentation”), double-checking your dosing procedures and checking the glass you are using.

I’ve been having the same issue for the last six batches of imperial IPAs. I make a clone of Russian River Brewing’s Pliny the Elder that goes from spot on in the secondary to rose-flavored maltiness that loses all its citrus/piney character two days after kegging. I’m very careful with sanitation and no common strains of wild yeast or bacteria were present when i had the beer analyzed. When I’ve asked Russian River brewer Vinnie Cilurzo and others, they suggest it must be oxidation since the beer changes so rapidly. I’ve tried to adjust my kegging process and used a longer siphon tube to make sure it reaches to the bottom of the keg and purged the keg with CO2 prior to the siphon. I cold crash in a refrigerator and the airlock reverses flow while the beer chills down, but I fill the airlock with Bacardi 151 to kill anything in the reverse airflow. Can the small amount of air that would enter during the reverse flow in cold crashing cause a significant oxidation issue? Or could my problem have something to do with my hops or bad CO2?
Jeffrey Gick
Leesburg, Virginia

I think the most difficult thing about trying to troubleshoot brewing problems in my column is not being able to taste the beers that I am being asked about. I sometimes flash to hearing car owners attempt to describe the sounds their cars make to Click and Clack on Car Talk. I just happen to be down the street from Monk’s Café in Philly and did have a pint of Pliny to help me imagine what may be happening! Based on your description, I think you either have an oxidation issue and/or hops that are not the best quality. Low-quality carbon dioxide is a possibility, but I would rank that pretty low on the scale. Another thing that may be happening is headspace scrubbing from the O-ring in your Corny keg, but this is another low odds explanation in my opinion.

So let’s talk about oxidation a little bit. These super hoppy beers do have aromas that are very sensitive to oxygen and the fresh hop aroma can quickly fade when these beers sit in a serving tank/keg for relatively short time periods when oxygen is present. While a small amount of oxygen may enter an airlock during cooling, the volume of gas sucked into the headspace is relatively small.

You did bring up this topic and it is something worth discussing. I personally have never liked the practice of allowing liquid in an airlock to suck into a fermenter when the fermenter is cooled because it simply seems inexact and it does not do anything constructive. Assuming the headspace volume is 1 quart (1 L) and the fermenter is cooled from 68 °F to 32 °F (20 °C to 0 °C), the ideal gas law tells us that 68 mL of gas must flow into the headspace to maintain a constant pressure. This means that there is a vacuum created in the headspace that must be balanced by 68 mL of gas being pulled into the airlock from the atmosphere and that the alcohol you put in the airlock will always be sucked into the carboy to allow gas to flow.

I would rather plug the top with cotton and simply allow the gas to enter without adding a shot of booze to my beer. The cotton ball plug is something that has a long history of use in microbiology labs and does present a handy alternate use if you really are worried about oxygen from cooling. You could insert a small hose in the headspace of your carboy, stuff in the cotton plug and very, very slowly flow carbon dioxide into the headspace during cooling. This would create a flow of gas out of the carboy and preserve the integrity of the headspace. I do not believe that this is going to solve your issues, however because this is not much gas.

The bigger possibility is within your secondary vessel. When a keg is flushed with carbon dioxide the contents of the keg still contain oxygen. A common misnomer with gas purging is that carbon dioxide displaces air as it “pistons” up the keg from the bottom; this argument looks good on paper but is not how things really happen in a keg. Temperature differential in the keg and gas flow into the keg both cause gas mixing to occur and this ends in a dilution effect versus what many envision as a blanket pushing up from the bottom of the keg.

And depending on how long the keg is flushed the oxygen content is likely to be high enough to pose significant oxidation risks; especially if the keg is shaken to speed up the carbonation process because this will also speed up the dissolution of oxygen. Brewers who have measured the oxygen content of gas flowing out of vessels being purged with carbon dioxide know that it can take a long time to achieve very low levels of oxygen in the tank. A much easier way to purge a vessel is to fill it up with water and then displace the water with carbon dioxide. Not only is this method fairly rapid, but it also consumes less carbon dioxide than prolonged purging. I do not like the effects of oxygen on beer and at Springfield Brewing Company we use several techniques to minimize oxygen pick-up. Filling our bright tanks with water and blowing them down with carbon dioxide is one and it is a very effective technique.

This was a long segment about keg flushing, but I think there are many brewers who think they are doing everything they can to reduce oxidation, when in fact they are barely scratching the surface of this topic. If you do everything possible to reduce oxygen in your beer and are convinced that you have oxidation issues, then looking at your carbon dioxide quality is something to consider.

If you ask your supplier for a carbon dioxide specification and they either do not understand the question or cannot get the information from their supplier, you may be using a low-grade supply. Many suppliers sell gas that is at least 99.95% and believe it is really pure carbon dioxide. The way I look at this is that the gas may contain 0.05% oxygen and this is enough oxygen to cause beer oxidation, especially if beer is force-carbonated with gas of this quality.

Hop quality is extremely important for brewers who are making the best hop bombs. These brewers are really serious about hop selection and doing everything possible to preserve hop freshness from field to the brewery and into their beer. I wrote about the Hop Quality Group in 2012 following a talk given by John Mallett (Bell’s Brewery) at the Craft Brewer’s Conference in San Diego. This group works with hop breeding programs, growers and processors to help their brewery-members further hop quality. Not all hops are created equally. Hops of the same variety differ based on numerous factors including where they are grown, the crop year (climate), when the hops are harvested, how the hops are kilned, die temperature during the pelletizing process, gas barrier properties of the package and hop storage temperature.

It is very difficult for small commercial brewers and homebrewers to select our ingredients because the likely truth is that the selection was done by others before the hops were processed and packaged. I am not at all suggesting that small brewers do not have access to good hops. It’s just that some of the really great hop bombs have been brewed with hops specifically selected for use in these beers and this selection goes way beyond knowing the hop variety.

One other thing that may be happening to your hop aroma is scalping by elastomers exposed to the beer. The liners on bottle caps are well known to adsorb hop aroma compounds and result in a decline in hop aroma during bottle storage. The same thing is possible with the large O-ring used to seal a Corny keg, although I have not read or heard any reports of this actually happening. There is no doubt that some aroma compounds are adsorbed by these gaskets because they smell hoppy. Good luck with trying to put the hop Genie back into your brew!

Issue: July-August 2014