My whole relationship with BYO started shortly after I completed my graduate studies in Dr. Lewis’ brewing program at UC Davis. At the time I was teaching and consulting with Dr. Lewis and Tom Shellhammer. Carl Landau, the founder of BYO, had moved to Davis and called the brewing lab looking for someone who may be interested in being the Technical Editor for his new magazine. My friend Scott Ungermann suggested that Carl contact me and that’s how it all began.
I don’t remember how I got nominated to write BYO’s Q&A column, but somehow I was slated to write the Mr. Wizard column and began answering some questions we dreamed up in the office for the Premier issue in the spring of 1995. I was not particularly shy at the time, yet for some reason I wanted my new column to be anonymous. There were many years when very few people, including friends, knew about my secret life as a homebrew columnist. The longer I kept my identity a secret the more fun the secret was to keep.
I moved to Missouri in 1997 to work for Paul Mueller Company in a new showcase brewery and to help with brewing and food related projects. There were times that keeping up with my new job and covert column were difficult but I was able to stay motivated by the challenging and interesting questions thrown at me from all over the United States and various homebrew spots across the globe. The thing that I really like is that my educational background in brewing and food science and my profession in brewing and process engineering are really useful when writing my column. Many of the questions I answer require research and my writing routine has become a great mental exercise that I really enjoy.
Cheers to 10 years and thanks for all of your thoughtful questions!
– Ashton Lewis
PREMIER 1995 Yeast pirates
My buddies call themselves yeast pirates because they visit breweries and swipe yeast samples. Is this legal?
Mr. Wizard wants to go on record right away that he doesn’t approve of the term “yeast pirate.” As far as the practice goes, your friends are not committing any federal offenses. However, I have seen some brewery job applications that ask: “Have you pirated yeast?” Mr. Wizard’s affirmative response to that question probably explains why he didn’t get the job. So if you want to “pirate yeast” be cool about it; no need to irritate anyone.
Now that we know it is legal, how does one swipe yeast? My marauding kit consists of one cigarette lighter, one sterile mason jar, one plate of wort agar, and one metal microbiology loop (all micro stuff available from homebrew supply stores). The mason jar is used to store some beer containing the yeast of interest in case the plating on site goes awry.
As far as the heist, I calmly order a pint of unfiltered beer and inconspicuously break out my mobile yeast lab. I first flame the loop, dip it into my beer and then streak it out on the wort agar plate. The plate is then sealed with Parafilm (a wax tape) for transport. The sample in the mason jar is my backup.
An easier way to get yeast from a brewery without permission is to culture it from a bottle-conditioned brew. I recently read a conversation on-line regarding how to get yeast from Sierra Nevada Porter or Stout. The answer to the question had something to do with buying Wyeast 1056.
My immediate thought was to culture the yeast directly from the bottle. I mean if you want yeast from Sierra Nevada porter, why buy it when you can culture it from a bottle of porter! If you do this, be careful. If the brew has any bacteria in the bottle, your yeast propagation process will also increase the bacterial population—not exactly the idea. Some breweries, like Sierra Nevada, are known for clean yeast in the bottle. Ask around to get a feel for the quality of yeast in the bottles of whatever brew you are looking to get yeast from. Be careful with some of the more exotic bottle-conditioned beers—many are filtered and dosed with a yeast strain that is different than the fermenting yeast. Some Belgian ales and hefeweizens use this practice. Alth-ough these yeast may produce good beer, they are not what fermented the host beer. So the short answer is that culturing a brewery’s yeast without their permission is legal. It’s sort of
like buying livestock; you don’t need permission to breed two animals that you bought.
In the case of beer, when you buy unfiltered beer you get the yeast along with it. Just remember, however, that many brewers protect their yeast because of the special character it gives their products. I don’t recommend going on brewery tours and opening tank valves or sticking your paw into open fermenters to swipe yeast while your gracious host is not looking. That kind of behavior is just plain rude and could cause contamination to the beer. It also tends to give us homebrewers a bad rap!
I keg all my beers but sometimes run out of refrigerator space. When this happens I leave my keg outside the refrigerator. My beer is not pasteurized, so how long can I safely store my kegs at room or refrigeration temperature before the flavor is affected?
They call me the Wizard, but a crystal ball I have not. The answer to your question has plagued brewers since beer was first conceived. Many famous scientists studied the spoilage of beer and wine, and Louis Pasteur developed the heat preservation technique now called pasteurization for beer, not milk. If brewers only knew how long their beer would last after packaging, distribution and packaged beer control would be so much easier.
The homebrewer and pub brewer do have it pretty simple, however, because the palate can tell when the beer no longer tastes as it should. So the simple answer to your question is that your beer’s flavor will remain unaffected by storage until your palate is able to detect that it has changed! At this point you may want to have a party and drink the rest of the beer before it becomes bad.
Professional brewers who choose to bottle, can, or keg their beer cannot use this simple method because distribution prevents it. When beer leaves the brewery, the brewer loses control over his beer’s fate. Some distributors try to torture the beer in hot warehouses, others move it from hot to cold and back to hot to try to see if the “cold-filtered” thing really worked, and others place it in tall stacks at the end of the grocery store aisle like little kids playing with building blocks. I’m sure if these distributors knew what they were doing to the beer, they wouldn’t do it unless, of course, they are just plain mean and nasty!
This is where the brewer really wants a crystal ball. They measure dissolved oxygen in package, use predictive microbiological tests, conduct simulated aging studies, and look at historical data to attempt to predict how long their beer will last in the hands of the distributor. Some distributors and beer retailers are very kind to beer and provide a cold, dark place for the beer to reside. In this sort of environment, beer can last for more than a year and sometimes several years before “going bad,” whatever that really means. The same beer may last only a couple of days in a less hospitable environment, such as a truck with no cooling stranded in Death Valley in July.
Based on all of these methods and a bit of guessing, some brewers put “best before” dates on their beers and others use “born on” dates. These codes allow the consumer to judge freshness before making a purchase. If everything goes as planned, the distributor will remove any old product before the consumer ever buys it and the date can be used as a guide at home.
In your case you are the brewer, the distributor, the retailer, and the consumer. If the beer gets old and starts to taste bad I would return it to the retailer and complain like mad. The retailer will trade the old stuff for new stuff with the distributor, the distributor will exchange it for new product with the brewer, the brewer will destroy the old product and, just like a commercial brewer, brew more beer to deliver into the consumer’s mug.
I know American beers are lighter today than before Prohibition, but are there records of the recipes used before all these changes? I look at labels on some of the bottles in my collection and see that some breweries claim to be more than 100 years old. I just wonder how much better the beer might have been, say when Pabst was first started in 1844.
Beer history is usually a subject I avoid, because my view of beer history is not in line with the mainstream, romanticized views of brewing in the old days. But this is one of those questions that really is hard not to respond to, so here it goes.
For starters, Prohibition caused tremendous financial hardship for the domestic beer industry, but Prohibition didn’t force brewers to brew light beers. There are many pre-Prohibition recipes floating about, and the differences between beer recipes of that era and beer recipes today are really not that great. American brewers of European descent were using starch adjuncts such as rice and maize (corn) decades before Prohibition. These adjuncts, among other things, lighten beer color and flavor. Brewers, a tremendously resourceful group, have used all sorts of starch sources over the several thousand years of beer brewing. The notion that rice and corn additives somehow make beers less beer-like has always puzzled me. After all, the loosest definition of beer is any alcoholic beverage whose carbohydrate is derived from cereal grains (as opposed to wine, whose carbohydrate comes from fruit sugars). In any case American brewers began using adjuncts long before Prohibition.
Many beer historians tie the lightening of American beer flavor, particularly hopping rates, to the rationing of foods during World War II. After the war ended the American palate was drastically changed. The bland trend was not reserved for beer alone. American food in general was bland, perhaps because Americans were accustomed to bland foods during war-time rationing.
Are American beers bland? Most microbrew drinkers would say yes. Ninety percent of domestic beer sales fall into the bland category, and Bud drinkers like their Bud. Was Pabst bland in 1844? No one alive today can comment on its flavor, but most American lagers of that period did contain adjuncts and probably had less character than their European counterparts. How much better were the beers back then than they are today? Read on!
In 1844 commercial refrigeration did not exist, pure yeast culturing had not been developed, the most basic understanding of beer spoilage by bacteria had not even been conceived, the word biochemistry did not exist and there was absolutely no concept of how yeast biochemistry in-fluenced beer flavor. In short, brewing science had not been born.
In 1844 beer was fermented in wood or concrete fermenters left exposed to the atmosphere. These fermenters were very difficult to clean, and bacteria were certainly full-time residents in breweries of the period. Without an understanding of microbiology, ease of cleaning didn’t matter because the brewers did not even know the true objective of cleaning. In 1844 beer was packaged in wood casks and exposed to air during serving. Oxidation and the proliferation of aerobic bacteria that turn alcohol to vinegar must have been commonplace.
In 1844 breweries used tools that would be classified today as crude. Life in the brewery was hard. In 1844 the beer consumer could not imagine what he did not have, and the beer industry did very well. Breweries that consistently made highly ranked beer stood out from the crowd, but all breweries of that period certainly had their difficulties. Modern brewers and beer drinkers need not look to the past with rose-colored glasses but instead should be in awe of the advances made over the past 150 years by the brewing industry.
Brewers were among the most inquisitive and open-minded thinkers of the 19th century in the fields of chemistry, biology, and food-processing technology. Enzymes were identified and defined by brewing scientists; Louis Pasteur revolutionized the world with his Etudes sur le Vin and his Etudes sur la Biere in the mid-19th century (these studies later gave rise to milk pasteurization); Emil Christian Hansen developed pure culture techniques for yeast in the late 1800s; and S.P.L. Sørensen, a colleague of Hansen at the Carlsberg Laboratories in Copenhagen, suggested the pH scale in 1909. All of these achievements were applied to different industries and spawned new ideas in the field of science.
Today, brewing benefits from advances in raw-material quality, advances in the understanding of brewing science, and advances in brewing technology.
Almost every homebrewer today understands that beer is damaged by oxidation. This most basic kernel of knowledge was not known by the commercial brewing industry at the turn of the century. Today, oxygen pick-up is minimized by design in the brewhouse, in the design of beer transfer systems, filters, and packaging lines.
Hot side aeration
Regarding BYO’s response (twice) to Dan Cole of Roanoke, Virginia, (Mail, August 1998, March 1999) about hot-side aeration (HSA). I think he has intelligently challenged you to answer a simple question with a real answer. You have twice told him that HSA is not a problem for homebrewers, but you have never given a researched or referenced answer as to why you believe this. A little explanation as to why the editor disagrees so strongly with Mr. Wizard as well as other feature writers would help settle this question.
Andy Lynch and
Before I jump head first into this colorful debate about hot-side aeration (HSA), I would like to explain where some of the comments in BYO mail and in some of the BYO articles stem. Most of the comments regarding this whole debate have come from commercial brewers who write for BYO.
To paraphrase, they have suggested to our readers not to worry about HSA too much because there are bigger problems to solve. Steve Parkes wrote that “the English homebrewer is more likely to be opening a can of extract . . . than worrying about excessive wort splashing causing hot-side aeration” (“Brewing Like the British,” December 1998 BYO). Some readers might have thought Parkes was saying that splashing hot wort could cause HSA, but I think his point was that American homebrewers tend to worry about things more than the English.
Dan Cole has asked for an experiment conducted by a third party to confirm or deny the existence of hot-side aeration. This would be a great experiment if the topic were new.
Fortunately for those interested in HSA, it is a well-researched topic and the research conducted over the years clearly shows that oxygen pick-up during mashing and mash transfer has an effect on beer flavor.
The topic of HSA can be divided into two areas: 1) aeration prior to wort boiling and 2) aeration after wort boiling. Malt enzymes, such as lipoxygenases and polyphenol-oxidases, that catalyze oxidation reactions are present in the mash and wort prior to wort boiling. In my opinion, this is where the HSA concern makes sense.
The second class of HSA is wort aeration after boiling. The only real consequence I have seen cited about aeration after the boil is an increase in wort color. Keep in mind that very hot wort, wort right after the boil, does not permit much oxygen into solution and under normal brewery conditions this won’t cause much wort darkening.
Anheuser-Busch (A-B) uses a device called a volatile stripper that forces hot air over thin films of wort after wort boiling to remove undesirable aromas such as DMS (dimethyl sulfide, which smells like cooked corn). Although A-B has adopted the philosophy of minimizing oxygen pick-up during mashing, mash transfer and wort collection, the company still uses the wort stripper to make very pale-colored beers.
Personally, I believe the body of scientific evidence surrounding HSA in relation to mash and wort oxidation prior to boiling is believable. Luckily, the problem is easy to control. Basically, don’t splash too much during mash-in, transfer from the mash pot to the lauter tun and wort collection. This seems so simple that most people don’t see the big dilemma. Today, mash mixers are designed with special agitator blades to minimize splashing during mash heating.
Lauter tuns are filled from the bottom to ensure a very quiet fill. Some experimental lauter tuns even operate under a slight overpressure from carbon dioxide. New brew kettles are filled from the bottom, and the worry about splashing has been designed out of the modern brewhouse. Even the beautiful and traditional wort grant has been replaced by wort collection piping systems that eliminate any exposure of wort to oxygen during transfer from the lauter tun to the brew kettle. After wort boiling, most breweries use whirlpool vessels to separate hops and trub from wort, and even these vessels are constructed to minimize splashing during filling.
As long as homebrewers exercise a little care, the likelihood of having HSA problems is very slim. The truth is that commercial brewers are concerned about HSA and that companies that manufacture brewhouse equipment have responded to these concerns by changing their designs of the past.
The confusing part for the homebrewer is that many writers who write for homebrew publications also work in the commercial-brewing arena, and commercial-brewing concerns frequently become homebrew concerns. Unfortunately, Mr. Cole felt like he was being brushed off by past comments stating that HSA is not much of a
problem for the homebrewer. For what it is worth, I don’t feel that HSA is a huge issue for most homebrewers. However, for those inquisitive homebrewers such as Mr. Cole, HSA is an interesting topic.
Recently I made a batch of American lager that had a “stuck” fermentation. I suspect that I underpitched and possibly under-aerated the wort. The final gravity was in the neighborhood of 1.025. Being somewhat impatient, I went ahead and kegged it to see how it would turn out. As I had suspected, it turned out to be sweet rather than crisp, due to the unfermented sugar. Will boiling the beer for about 15 minutes to drive off the carbon dioxide, then re-aerating and re-pitching correct the problem?
This doesn’t sound like the best idea. For starters, boiling your beer for 15 minutes will evaporate most of the alcohol from it. The other negative effect of this plan is severe oxidation. This would occur because of oxygen pick-up when the beer is transferred from keg to kettle and then kicked into high gear when the beer is heated to boiling. So far we have produced oxidized, non-alcoholic, sweet beer. Mmmm! The next step of your plan is to re-aerate and add more yeast. This would work to ferment the residual sugars and you would end up with a very low alcohol, oxidized beer.
The notion that your under-attenuated beer can be fixed is correct and I think it can be done in a much easier way. I would begin by transferring the beer in the keg to a fermenter, securing the top with an airlock and storing it at fermentation temperature for a few days. This allows most of the carbon dioxide to escape from the beer. The remaining carbon dioxide won’t inhibit fermentation and should be low enough to prevent excessive foaming.
Next, make a small batch of wort from dry malt extract. I would use about one pound of dry malt extract, 5 quarts of water and 1 AAU of hops (0.1 ounce or 2.4 grams of 10 percent alpha hops, for example). Boil this for one hour and adjust the volume to one gallon. Then cool, aerate and add yeast. Ferment at room temperature until it begins rapidly fermenting (high-kraeusen stage). This should happen in 24 to 48 hours, depending on how much yeast you added. When high kraeusen rolls around, add this to the contents of your fermenter. Monitor the fermentation until complete, transfer to your secondary, then age and keg as you did before. My advice for the future is to be patient. In this case you could have kraeusened the beer before you jumped the gun and kegged a batch of half-fermented lager.
Foam and proteins
I have been homebrewing for several years and still have a persistent problem with head retention. I brew all-extract batches with some specialty grains, but do not mash. I have heard that using carapils and going heavier on the hops can aid in head retention, but I still can’t keep a head on the beer for the whole glass.
Rolling Meadows, Illinois
Beer foam is pretty neat-looking stuff and is one of those topics that brewers can only discuss with other brewers. Start talking about the merits of good foam among non-brewers and people will think there is something fundamentally amiss! I have spent a lot of time looking at and thinking about beer foam — in fact, I did my masters thesis on beer foam — and have developed a simplified approach to brewing beer with great foam.
The key item involved in my approach involves malt selection.
This means going all-grain. Unfor-tunately (for extract brewers), all-grain brewers really have a leg up on extract brewers when it comes to foam for a few reasons. First of all, foam is primarily a function of wort or beer protein content and type. Protein (or more correctly polypeptide) content decreases when wort is heat-treated, because proteins come out of solution (the wort) when heated. Extracts are heated and sometimes boiled when produced, and the brewer again boils the wort at home (unless you’re making a no-boil beer). Another key factor affecting beer foam is the type of malt used. Extract brewers can select different specialty malts but have no control over the type of malt in the extract, which typically comprises more than 85 percent of the recipe. Plus, some extracts contain adjuncts, for example sugars, which dilute the protein content even more and have a negative affect on foam.
When selecting extracts look for all-malt, low-color types, since these will give you the best shot at good foam. I personally prefer dried malt extract (DME) over liquid extracts. This is because DME receives less heating in the process. Some extracts will describe the wort it will produce. If you can find un-hopped, all-malt extracts that use the descriptors “light color” or “lightly modified malt,” you will be in good shape.
I recently brewed a Pilsner using a new malt, produced by Briess, that’s simply called Pilsner malt. The malt caught my attention because Briess has spent a lot of time and energy on developing an under-modified malt. Their advertising mainly described its low color and very light flavor. I was more interested in the type of foam it would produce. So I bought some of the Pilsner malt and some Czech Saaz hops and got busy!
The first thing I noticed about the malt was its color. This stuff is really pale and the color is a sign of little protein degradation during malting. Darker pale malts are usually well-modified because modification leads to protein breakdown. This leads to an increase in smaller protein bits (polypeptides) and each polypeptide has a reactive site that can participate in the Maillard reaction during kilning. The Maillard reaction is responsible for malt color and flavor. Therefore, color is loosely related to modification.
During wort collection it was clear that this was going to be a very pale wort. The next observation was indeed memorable! As the wort was heated, large flocs of protein began to form. This is typically seen after the boil, but I have never seen big protein flocs prior to boiling. Then when the wort finally came to a boil, this magnificent meringue-like foam emerged. Now that the wort has been fermented, the beer is lagering. It is currently carbonated, cold and aging. I have taken several samples and have never made a beer with such an incredible foam.
So here is my simplified approach to brewing beer with good foam: 1) begin with under-modified malt if you really want killer foam (use special malts as normal for color and flavor), 2) avoid using protein-free adjuncts like corn, rice and sugar, 3) never use any soapy cleaner or sanitizer without a very thorough rinse, 4) use really clean beer glasses.
There is one major problem with this approach. Most pale malts are not under-modified and there are some real benefits to using well-modified malt. There is a trade-off with everything. If I am correct about malt modification being a primary factor in
foam stability, then foam stability will progressively decline as malt modification increases.
If I wanted to use oak or beechwood chips in brewing a 5.5 gallon
(21-L) batch of beer, how would I go about it? How many ounces would I use and how would they be handled in the mash or fermentation containers? How long would they be left there? I realize that they would have to be steamed for 15 minutes before using.
Paul A. Borowski
You have really asked two different questions here: How to add oak for flavor and how to add beechwood for aging. Beechwood does not not add flavor. Adding oak chips — which is done in the fermenter, not the mash tun — can add some interesting flavors to your homebrew and act as a surface area to accelerate aging.
Whether using oak for flavor or beechwood to help with aging, the weight of the wood chip is not the most important consideration. Rather, the surface area is the key factor to consider. The flavor from the chip is released into the beer only where the beer and the chip are in contact. You could have a bag of thin oak chips and a bag of thick oak chips that both weigh the same, but the thin chips would have a greater surface-area-to-weight ratio. So the thin chips would add more flavor than the same weight of thick chips.
I recently made some oak-aged hard cider and got an incredible aroma from the wood during the aging process. The barrels I used are about three feet in diameter, four feet long and contain 50 gallons (190 L) of liquid. To put this in beer-geek terms, the barrels have about 149 square inches of oak area per gallon of contents. This statistic is the barrel’s surface-to-volume ratio. That’s a good number to keep in mind, since most barrels used for aging wine are in this size range. As the capacity of a barrel increases, its surface-to-volume ratio decreases and the time required for the oak to flavor the contents of the barrel increases.
I chose an American oak, with a medium toast and a “normal” surface roughness. According to the barrel maker, this would give me nice vanilla notes from the toast level, an aroma consistent with American oak. The roughness of the interior would result in a faster release of oak flavors than a barrel with a more polished finish. Most of these same options are available when buying oak chips that are added to the aging vessel.
Right now it’s summer, a good time to brew a big beer for the winter. Imagine a strong ale with assertive bitterness, low hop aroma and a full and clean malt backbone. This beer has just finished primary fermentation and the plan is to age it on oak to add further complexity to its flavor. A bag of oak chips with the desired toast has been purchased and the question is how much to add. If the chips are two inches wide, four inches long and 0.25 inches thick they will each provide 19 square inches of surface area (two sides at eight square inches, two edges at one square inch and two edges at 0.5 square inch). Eight of these chips per gallon of beer will give about the same surface-to-volume ratio (149) as an oak barrel. So set aside 43 of these chips for the 5.5-gallon (21-L) batch.
Chips will float and it is important to keep the entire surface of the chip in contact with the beer during aging. A hop bag weighted with some stainless steel bolts (or some other inert weight) will do the trick. Sterilize the bag, chips and weight with either steam or hot water. I chose to fill my barrels with 195 °F (91 ºC) water and let the barrels sit for several hours prior to use. Either method will work for sterilization. Some sanitizing solutions will damage the wood and perhaps flavor the beer. Burning sulfur is one method of sanitizing barrels used by winemakers, while using a dilute solution of KMS or Campden tablets is another. I like hot water because there is nothing added to the barrel other than water.
The next step is to place the chip bag into a vessel for the aging process. This poses a dilemma since the chip bag won’t fit into a carboy and a plastic secondary allows oxygen into the beer. The ideal container is a 5-gallon (19-L) Cornelius keg. Place the chips in the keg and rack the beer from the primary into the keg for aging. Try to minimize the amount of yeast carried into the secondary as excessive yeast will impart autolyzed flavors from yeast death over the aging period. The beer can be primed at this time or you can wait until later. Priming at this stage will be easy since the yeast viability is still excellent. If primed later, more yeast will most likely need to be added.
Now it’s time to wait. This is the most important step to oak aging. It is tempting to place the keg in a cool corner and to forget about it for several months. Vigilance and restraint are required during aging. Sample the beer on a regular basis — say once every three weeks — to keep tabs on its progression. The purpose is to prevent the beer from becoming excessively oaky. The oak should add complexity to the beer, but not dominate its flavor. Once the flavor reaches the intensity you desire, you can rack the beer into a second keg or bottle it.
Another variation is to not worry about the oak intensity during aging and to blend the oak-aged beer with a batch of non-oaked beer to produce the desired oak intensity. This is how I treated my cider, which became so oaky after three months in a new barrel that it was hard to smell or taste anything but oak!
You also mentioned beechwood in your question. Beechwood aging has absolutely nothing to do with wood flavor. The wood gives the yeast more surface area to cling to and helps the beer age. Diacetyl and acetaldehyde reduction during aging requires yeast and beer to interact, and that is precisely what the beechwood chips do for the brewer.
Can you overdo the O2?
How long would I have to aerate with oxygen in order to incur negative effects on my yeast? I have read several articles that skirt the issue, but most cover commercial brewing and don’t give homebrewers an idea of how much is too much. I have read the recommended length of time to aerate, but not the maximum times.
It sometimes seems like homebrewing has advanced from “Relax, don’t worry, have a homebrew” to “Stress out so much that only a homebrew can calm you down.” Unfortunately, there is no exact answer to this question. To leap-frog to my recommendation, I encourage homebrewers to worry more about under-aeration and not to spend too much time on concerns with over-aeration. The caveat is with propagation. Yeast can be stressed when oxygen is continuously or intermittently bubbled into a propagation container. I will give some insight that may help understand why there is no exact answer to your question and will present a list of facts about oxygen and yeast that may help.
For starters, not all brewing yeast strains have the same oxygen requirements for satisfactory fermentation. This observation is documented in Malting and Brewing Science, Volume II (Hough, Briggs, Stevens and Young), although many practical brewers know this to be true from anecdotal evidence. This book has a very nice graph showing peak yeast density as a function of wort oxygen content at the beginning of fermentation. The graph shows a dramatic increase in yeast density as oxygen levels increase from 0 mg/L (which equals 0 ppm) to 2 ppm and very little change from 2–8 ppm. Another graph shows the relationship between the duration of fermentation and wort oxygen content at the beginning of fermentation. This relationship is a bit more interesting since fermentation time decreases as oxygen content increases.
In the book Brewing (Lewis and Young), the point is made that alcohol content in beer declines as wort oxygen levels increase. This reduction can be greatly exaggerated in fermentations that are continuously aerated, such as yeast propagation. Cell density in a commercial propagator with aeration and stirring provisions can reach as high as 200 million cells/mL; this is about five times higher than the peak density seen in a typical beer fermentation where the fermenter is neither aerated nor stirred.
The explanation for this phenomenom is relatively simple — alcohol is not produced from glucose when yeast are consuming glucose to synthesize the building blocks for new yeast cells. Wort aeration also has a dramatic influence on beer flavor formation during fermentation because it affects yeast metabolism. For example, if wort oxygen is limited then ester production increases and, in turn, the production of fatty acids within the yeast cell is limited. Likewise, fatty acid production increases with wort oxygen level and ester production decreases.
Yeast propagation is really the place in commercial breweries where over-aeration has been examined. Why? Because yeast propagators are equipped with sparging devices designed to deliver a lot of air to the propagation and increase cell growth. After all, the goal of propagation is growing yeast and not making beer. Both practical brewers and brewing scientists have ob-served that yeast can be damaged when excessive amounts of oxygen are delivered during propagation. The term used to describe this stress is “oxidative damage.” While oxygen is required for a wide array of biochemical functions, it is also related to cellular aging. The free radical theory suggests that cellular aging results from damage caused by reactive oxygen species known as “free radicals” — sounds like a punk rock band!
Veronique Martin of Oxford Brookes University present
ed a poster at the 1999 European Brewing Congress (EBC) in Cannes entitled “The Oxidative Stress Response of Ale and Lager Yeast Strains.” This poster showed stationary phase yeast (the phase after the increase in yeast density) to be less sensitive to oxidative stress than cells growing during the exponential growth phase. Furthermore, the negative affects of oxidative stress show up in subsequent fermentations that use yeast cropped from a stressed environment.
At the same EBC meeting, Chris Boulton from Bass gave a talk called “A Novel System for Propagation of Brewing Yeast.” This method uses oxygen injection into the propagator. The purported advantage of this method was that yeast did not get exposed to oxidative stress during the sensitive growth phase of their life cycle. This is clearly a topic without an exact answer as research is ongoing. In fact, much of the research is believed to relate to aging in humans and other animals. I will close with a list of facts and my own opinion.
Fact: Wort oxygen levels very quickly drop after the lag phase of fermentation ends when aeration or oxygenation is performed only once. This is the typical method of aerating wort.
Fact: Wort has an oxygen content of about 8.5 ppm when saturated with air (79% nitrogen and 21% oxygen) and an oxygen content of about 43 ppm when saturated with oxygen.
Fact: 0.57 liters of oxygen at standard temperature and pressure weighs 813 mg. When dissolved in 5 gallons (19 L) liters of wort, this results in a concentration of 43 ppm. After the saturation point is reached, no more oxygen can be dissolved into wort. In other words, it doesn’t take long to saturate wort with oxygen (or air when aeration is being performed).
Fact: Oxygen content in wort cannot be known without measuring it since wort temperature, gas bubble size and the contact time between the bubble and wort all have a profound effect on gas diffusion. Small bubbles diffuse much, much more quickly than big bubbles. Small bubbles also are less buoyant, rise slower through the wort and as such have a longer contact time. That’s why aeration stones are de-signed to produce very fine bubbles.
Fact: The major concerns with commercial brewers and over-aeration are primarily focused on propagation where aggressive aeration and oxygenation can cause problems due to oxidative stress.
Opinion: This topic has incredible depth and becomes extremely confusing if one attempts to create a Unified Theory of Aeration. There is no exact answer to your exact question. Homebrewing is a hobby of exploration. I think the idea is to learn from what others have done and explore the art of brewing in a fun and creative manner. Along the way, the experienced brewer will come up with their own special techniques and interpretations to the tremendous number of ideas floating around the brewing (and homebrewing) world.
I personally use pure oxygen for a one-time saturation shot for yeast propagation. I have never had any problems with this method. When it comes to wort aeration for making beer, I use air and saturate with air. Again, this works well for me and, most importantly, my yeast!
Please solve an argument between my homebrew buddies and myself. What, in your opinion, is the hardest kind of beer to brew at home and what is the easiest?
I can’t believe a couple of homebrew buddies would argue over such a thing. I suppose these discussions are just part of this great hobby! I view beer in a similar light as music.
Music combines different individual sounds into a total sensory experience. In music, the extremes of this total sound combination seem the most challenging to produce. On one end of the spectrum, compositions that sound excessively simple (don’t you love oxymora?) are often difficult to play. The jazz standard “Four” by Eddie Vinson (often credited to Miles Davis) is an example of a really simple composition that requires an excellent group of musicians to play successfully.
The other musical extreme is huge orchestral compositions where disaster occurs if every note is not played at the right time and tune. Johann S. Bach composed pieces with amazing complexity that challenge both musicians and the instruments they play. Bach’s intricate compositions were commonly used in his day to tune organs.
In the middle are tunes like Sir Mack Rice’s “Mustang Sally.” This catchy little ditty is one that almost every local blues band can crank out with confidence and few mistakes.
The Mustang Sallies of homebrew are beer styles like pale ale, American-style wheat, hefeweizen, stout, porter and brown ale. If you have good ingredients, an appropriate yeast strain and know the basics of brewing, you can brew these styles at home with ease and consistency. These are the types of beers that are great to offer friends and watch the expressions on their faces. It’s like they are saying, “Wow! You brewed this at home?”
Notice that none of these beers are lagers. Since lagers are fermented and aged at temperatures that are much cooler than the average home, they require special equipment that put them into a more advanced homebrew category. The other commonality among these beers is that they have enough flavor intensity to cover up minor faults. Styles that have light, subtle or refined flavor complexity are much more difficult to brew than big beers with over-the-top flavor. This is a point of debate among many brewers because it suggests that the big commercial brewers are actually producing a difficult beer style. You can beat up the “budmillcoors” of the world for brewing beer with little flavor, but you really can’t argue that they lack skill.
If you are having a hard time swallowing this (no pun intended!), try brewing an American-style lager and compare it to a commercial example. European styles like Pilsner and helles lager also fall into this category because they have few ingredients and a simple, yet elegant flavor profile. Faults in these beers stand out like a coffee stain on a white shirt.
The symphonies of beer include heavy hitters like barleywine, doppelbock, all sorts of Belgian ales and styles that are intentionally soured by bacteria. Although these beers have a lot going on in the flavor department, they require balance to taste good. It’s tempting to go nuts with these beers and to over-emphasize one component of the beer. For example, over-hopped barleywines, cloying doppelbocks, over-spiced Belgian ales and soured beers that taste like some microbiology experiment gone awry seem more common than exquisitely balanced versions of these same styles.
I am sure that I have not solved your argument, but I have presented my opinion to this “no-right-answer” style question. I can honestly say that my best beers usually fall into the Mustang Sally category, although I have brewed really tasty lighter beers and some equally delicious big beers. I tend to be my own worst critic and find more faults with beers that venture towards the lower and upper extremes of flavor . . . happy debating!
My neighbor and I have been doing single infusion mashes for about four years. We started doughing in at 104 °F (40 °C) and holding this temperature for 20 minutes. This has increased our efficiency. We have read that instead of doing a single infusion, it is better to do a step at 140 °F (60 °C) and a step at 158 °F (70 °C) for a total of one hour, with the understanding that the amount of time spent during the hour at 140 °F and 158 °F will change depending on the brew you’re making. What’s your take on this advice?
David Reaser & Ray Redcay
The topic of mashing technology and mashing biochemistry is a topic of deep personal interest and is one that I have written much about over the years in this column. I advocate using certain brewing implements and brewing techniques when needed. Mashing is certainly an area where different options abound. A brewer can choose from infusion mash tuns, stirred mash mixers (heated pot and spoon for the homebrewer), double mash set-ups for either decoction or adjunct mashes and then a whole sub-set of options for the type of wort separation method. When it comes to the mash profile itself, the options are wide open since the mash profile is a combination of temperatures held for various times to accomplish the brewer’s goal.
The brewer’s goal is where I keep my attention glued. There are many new brewing technologies springing up in the world of commercial brewing that attract many brewers because the methods are new, and this attraction to technique often takes the focus off of the most critical element — namely the brewer’s goal!
The brewer’s goal in mashing is two-fold. The primary goal is to convert starch from the variety of starchy ingredients into fermentable sugars so that yeast may gobble them up and transform wort into beer. This goal is crude and we can accomplish our
primary goal and produce beers with a very high residual extract as well as those with virtually no remaining carbohydrates.
The secondary goal of mashing, and arguably a much more important one, is to take control of the transformation of starch. In order to control these reactions it is critical to understand the reactions themselves and this means boning up on mashing biochemistry — aka enzymes. I will avoid covering this topic in depth because I want to cover new ideas, but here’s a quick rundown on enzymes in the mash.
Enzymes are most active when their “temperature optimum” and “pH optimum” are both met. If the mash temperature exceeds the optimum temperature of a specific enzyme, say beta-amylase, the enzyme irreversibly denatures and permanently loses activity. The various relevant enzymes active in malt have a range of temperature optima from 104 °F (40 °C) to 158 °F (70 °C).
The rate of enzymatic reactions is highest when the concentration of enzyme and substrate are high. This means that reaction rates drop off as time passes and there becomes a point of diminishing return where extending the mash time does not have any real affect on the mash. It also means that if the concentration of a certain enzyme group is very low in malt, for example proteolytic enzymes, there will not be much change in the wort attribute by the enzyme group. In other words, if they ain’t at the party, they can’t contribute to the fun!
Most all-grain brewers are fluent in the material above and many can recite the various temperatures and en-zymes active over these ranges as easily as their own birthdays. The real question is picking the appropriate tool for a particular brew. This requires defining the finished brew and choosing a strategy to get there.
At the most recent Craft Brewers Convention in San Diego, Dr. Michael Lewis and Dr. Charlie Bamforth (past and present brewing science gurus at U.C. Davis) gave a wonderful presentation where they challenged brewing practice and demanded us as brewers to defend why we do what we do.
To rephrase the thought, they challenged the audience to think about the brewer’s goal and to critically evaluate their methods selected to strive towards this goal.
One of the many topics covered was mashing time and temperature. Many big brewers have gotten side tracked in the last year with their
inexplicable pursuit of low-carb beers. Anheuser-Busch, the company many believe to have accidentally created this monster, has recently gone after the South Beach Diet because this diet has incorrectly labeled beer as high in carbohydrates, specifically the disaccharide maltose. It seems that the author of this diet never studied microbiology and fails to recognize the fact that yeast consume maltose to transform wort to beer.
Before we had low-carb beers, we had light beers and for a brief flash of U.S. beer we had dry beers, which continue to remain very popular in Japan where the style first began with Asahi Super Dry. All of these beer styles require long, multi-temperature mash profiles unless the brewer decides to use exogenous enzymes (enzymes from a bottle). The result with these commercial trends is that many brewers have felt the need to use multi-temperature mashing because other brewers do it. This is not the best reason for the choice of method.
Further back in beer history, Germans used decoction mashing and, more recently, step mashing to produce wonderfully delicious lagers. The conclusion by many is that these mash profiles are required to produce great lagers.
The Lewis & Bamforth talk had a take home message that was so refreshing in the obvious Homer Simpson “Doh!” sense . . . malt today is not the same malt we read about in text books. Modern malt is powerfully enzymatic and usually very evenly modified. It is also much paler than malts of yesteryear. The suggested mashing strategy was to minimize mash time in an effort to get the good things from the malt and to minimize the extraction of the unwanted compounds, such as the flavors from the husk that can give a gold brew astringent or grainy characters. Measuring yield, which you are doing, is a good measure of success when it comes to mashing.
Another key variable to consider is fermentability. If your goal is a dry beer and you are not going as low as you like, you may need to add some lower temperature rests; 140 °F (60 °C) is a good rest for this purpose.
In your case, if a simple infusion mash is not providing the flexibility in wort profile required to brew the beers you desire, change it. If your beers taste great and your goal is to be more efficient be careful. Increasing efficiency usually comes at a price. That price may be buying a better mouse trap, inventing a better mouse trap or sacrificing flavor for efficiency. My advice to you and your neighbor is to brew the same beer with your old and new methods. Compare the two methods by measuring initial and final gravity, calculating your efficiencies and tasting the finished brews. To paraphrase a recent ad campaign, “No brewing technique is 100% efficient . . . choose on taste!”