The final

Our final exam is tomorrow. This has been a point of moderate stress for the brew crew.

In the past ten weeks, we've covered thousands of pages in textbooks, slide shows, pamphlets, lab manuals, and articles on brewing. We've spent 350 hours in class, and the course has kept a consistent, "if it's Tuesday, we must be studying yeast" kind of clip, which is to say that review and repetition are not highly prized in World Brewing Acadmey pedagogy. And tomorrow, we write our exam: there will be seven essay questions, and you answer five of them. To pass, you are required to get an 85%. Anyone who scores between a 50 and an 84 must take an oral exam--administered by scary German brewing instructors--when we return from our European brewery tour. Score below a 50, and you leave diploma-less.

Despite the temptation of Munich beer life, folks have been pretty studious the last few days, and there seems to be a direct correlation between amount of studying and anxiety around the exam. Rightfully so; every one of us is probably more invested in this exam than any we took in high school or college, and the volume of information that might be on it is intimidating. In the last few days, I've pulled out all my old tricks for studying for a big exam (though, I don't know that I've ever taken one whose breadth is quite so, well, broad). Flash cards, typed outlines, diagrams, tables, oral pop quizzes on the train with friends, study sessions in front of a big blackboard, and reading and re-reading. My final effort, to both solidify my baseline knowledge and to try out a new study format, is this: studying via blogging.

So I've guessed, and answered, the questions that I expect to see on the exam. Once the deed is done (and we've all opened our bottles of Triumphator Doppelbock afterwards), I'll let you know how I fared. Back in middle school, I was pretty good at predicting who the Oscar nominees would be in any given year, so maybe I'll get a couple right. If I don't, I may have an oral exam to study for.

The rest of this entry is for the beer geeks. See how you do on the pseudo-final. The answers are included in the first comme

1. Raw Materials: Malt Analysis
Q: Your brewery receives a shipment of pale malt with the following analysis from the maltster. Discuss the values below, identify whether they are "in spec," and explain how this malt might perform in the brewhouse. What steps might you take later in the brewing process if you were using this malt to brew a pilsner?

moisture content 4.2% pH 5.7 sacc. time 7 min.
apparent deg. attenuation 85% extract 82% friability 94%
Total % Protein 10.5%
F-C 1.5% friability (glass) 2% Kolbach Index 49%

A: In general, this is a high quality, if slightly overmodified malt. The only measurements that are "out of spec" are the friability (acceptable range 80-90%), saccharification time (10-15 minutes), and the Kolbach Index (38-43%). The off values in all three of these areas suggest that the maltster allowed enzyme activity to continue too far during germination. Nonetheless, the malt has an appropriate level of total protein and shows good potential for B-amylase activity given its high extract %. This malt will produce a wort that is highly fermentable, with few residual dextrins (given the high alpha amylase activity); however, it will be imbalanced with regard to different types of proteins. Specifically, it will favor high free amino nitrogen levels, which will make for good fermentation, over higher molecular weight proteins that are essential for foam stability and saturation of carbon dioxide. To brew an excellent pilsner with this beer, a brewer could add dextrin malt (aka "carapils") to the grain bill, skip a protein rest during mashing, and/or use a foam enhancing agent such as alginate.


2. "Hot Side" Brewhouse Operations
Q: List the components of a classic "4 vessel" brewhouse. Discuss the role of each in the production of wort, and give specific examples of ways that each part of the brewhouse process impacts the final character of beer.

A: The four vessels are the mash tun, lautering tun, wort kettle, and whirlpool. In the mash tun, milled malt is mixed with hot water in order to solubilize sugars, proteins, and minerals into a solution that eventually will become hot wort; during this process, complex starches and proteins are broken down into simpler sugars (such as maltose, glucose, sucrose, maltotriose, and unfermentable dextrins) and smaller polypeptides, amino acids, and nitrogen, respectively. Lautering separates the liquid wort from spent grain by using the milled husks of malted barley as a natural filter bed. Later, the lautering process is completed by sparging, in which additional sugars, proteins, minerals, and polyphenols are "rinsed" into wort and the total volume of liquid is increased. This hot wort is then boiled for anywhere from 30 to 90 minutes in order to sterilize the liquid, evaporate excess water and distill the dissolved extract, isomerize essential alpha acids from hops, volatilize undesirable compounds, form a hot break of undissolved proteins and polyphenols that are undesirable in finished beer, fix the carbohydrate profile of the wort through the denaturizing of enzymes, and form additional color and flavor compounds via Maillard reactions between sugars and amino acids. Finally, the whirlpool separates the hot wort from the trub of proteins, polyphenols, and hop matter that can interfere fermentation and beer stability. As it leaves the whirlpool, beer is cooled for fermentation and cellaring.

In terms of flavor or "character" impacts, each step in the process is critical. During the mash, a brewer controls time, temperature, thickness, and pH in order to stimulate enzyme activity that may create a lghter- or heavier-bodied beer. Similarly, certain rests during the mash can impact yeast behavior during fermentation. The classic example of this is using an extended protein rest to increase ferulic acid production during fermentation, which helps contribute a distinct clove flavor to certain German and Belgian-style ales. Lautering requires special precision on the part of the brewer: temperatures that are too high in the lautering tun will leach undesirable, astringent tannins into the final beer, and temperatures that are too low will create a beer that is highly viscous, difficult to filter, and hazy. During the boil, a brewer controls the "hop character" of beer by determinging when to add additions: a brewer who desires significant hop aromas without accompanying bitterness may wait to add her additions until late in the boil. A vigorous boil also helps remove DMS (dimethyl sulfide) from the wort--DMS can impart an undesirable cabbage, vegetal, or corny flavor to beer. Finally, proper whirlpooling removes compounds that can negatively impact yeast performance. Poor fermentation can lead to high levels of diacetyl, acetaldehyde, haze, and oxidation.


3. Fermentation Off-Flavors
Q: What is acetaldehyde? Why is it produced during fermentation? How can a brewer "fix" a beer with acetaldehyde?

A: Acetaldehyde is a specific aldehyde that is produced as an intermediate byproduct of fermentation. All healthy fermentation produces acetaldehyde; however, its presence in finished beer is consider a negative characteristic. Typically, it is associated with flavors of green apple or grape skin. I personally find that it has the aroma of raw pumpkin.

Yeast produce acetaldehyde as part of the complex process that converts glucose into ethanol. In order to produce biologically useful energy (ATP), glycolysis occurs inside yeast cells. During glycolysis, glucose uses NAD and ADP to create ATP, hydrogen, and pyruvic acid (converted to pyruvate to maintain internal pH of the yeast). The yeast then "wants" to get more NAD in order to continue to produce energy and grow. This is why fermentation occurs, and it is where acetaldehyde enters the equation. Pyruvate undergoes an oxidative decarboxylation, a fancy way of saying that it loses carbon dioxide, and is converted into acetaldehyde. The "natural" next step undertaken by healthy yeast, with a sufficient amount of zinc, is to turn that acetaldehyde into ethanol and NAD. In other words, acetaldehyde is the compound produced en route to "getting NAD back" during fermentation.

Acetaldehyde correlates directly to yeast stress: that is, any criteria that negatively impacts yeast health and vigorous fermentation increases levels of acetaldehyde. This includes high yeast pitching rates, high pressure inside a fermenter, and low free amino nitrogen in wort. High fermentation temperatures increase acetaldehyde production and speed its conversion into ethanol. Typically, beer with high levels of acetaldehyde require a longer fermentation, krausening, or a fresh dose of yeast, all of which are acceptable techniques to "fix" this off-flavor.

4. Brewery Microbiology
Q: You lead the microbiology lab at a large lager brewery. You detect a bacterial contamination from pediococcus in your beer. List the steps that you have taken in the lab to identify pediococcus as the culprit of beer spoilage, including "sensory" tests.

A: There are three basic tests that breweries use to identify microorganisms: the gram stain (or KOH test), the catalase test, and basic microscopy. All bacteria can be categorized as either gram negative or gram positive. This means that when stained, the outer membrane of the bacteria appears bright under the microscope and is an indicator of the basic structure of the bacteria. Typically, more resilient bacteria are gram positive, including the primary class of beer spoilers: lactic acid bacteria. As an alternative to the gram stain, many brewing scientists prefer the KOH test. In a lab a cultured microorganism is mixed with a little bit of KOH. If the resultant mixture is "ropey," the organism is KOH positive. The KOH and gram tests are inversely correlated.

The Catalase test determines whether a microorganism is aerobic or not. Hydrogen peroxide is dropped onto a microogranism on a lab plate; if there is a bubbling reaction, the organism is respiring and thus aerobic. Pediococcus is catalase negative, whereas other micrococci that are not beer spoilers are usually catalase positive. A beer spoiler that is gram positive (KOH negative) and catalase negative is either pediococcus or a type of lactobacillus. The final identification can be done by microscopy: using a simple microscope to identify the organisms shape. Cocci are round whereas bacilli are rod-shaped. A pediococcus infection can be identified organaleptically as well due to its distinct "rancid butter" aroma and flavor in beer.

Other common beer spoilers include lactobacillus, acetobacter/gluconobacter, enterobacteriaceae, megasphera, pectinatus, and zymomonas.


5. Brewhouse Calculations: Grains, Hops, and Efficiency
Q: Calculate the malt and hop requirements for a 500 liter (cast out wort) batch of American pale ale with an original gravity of 15 degrees Plato (by weight) and 55 IBUs. Select appropriate American hop varieties, and give plausible alpha acid percentages for each addition. Your brewhouse has an overall efficiency of 82%, and you typically have a 26% utilization on hops.

A: 1. Malt calculation
Malt (kg) = {volume of wort (hl) x .96 x gravity (g/100 ml)} / brewhouse efficiency (%)
= (5 hl x .96 x 15.89 g/ml) / 82
= 93.01 kg

2. Total Alpha Acids Required
AA (kg) = {volume of wort (liters) x target IBU (g/ml)} / hop utilization (%)
=(500 x 55) / .26
=105.77 g of AA

3. Distribution of AA for Each Addition
1st Addition: CTZ (bittering) 16%AA 50% =52.885 g AA
2nd Addition: Cascade 6% AA 20% =21.154 g AA
3rd Addition: Cascade 6% AA 30% =31.731 g AA

4. Actual Hops Required
hops (kg) = kg AA / % AA
1) CTZ = 52.885/16% =330.53 g
2) Cascade = 21.154/6% =352.57 g
3) Cadcade = 31.731/6% =528.85 g




So those are the five questions, I plan on answering. How did you do? Dark horse topics that might show up: fermentation regimes; quality control around beer haze, gushing, foam, or flavor; filtration; and water chemistry. Stay tuned to see if I score as well at predicting the test as I do on it.

Bis dann...