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How to Read Fishbones

Cause and effect relationships

First generation fishbone diagrams were stereotypical in that the content was strictly limited to cause and effect relationships. For example, an early fishbone with “beer flavor stability" as the "effect" would depict "causes" such as TIPO (total in package oxygen), temperature, and beer [SO2] as impacting flavor stability. To avoid my usual propensity for drafting long-winded statements to indicate the nature of the relationship between a cause and effect, I elected to simply denote causes having a direct relationship to the effect by placing the (+) symbol at the end of the cause while causes with inverse relationships were denoted with a (–) symbol. Thus, in the case of the effect "Beer flavor stability," the relationship between it and TIPO is denoted by the symbol for an inverse relationship, namely (–). This means that as TIPO levels increase in packaged beer, beer flavor stability is claimed to decrease. In the case of beer [SO2], however, the relationship is direct, with (+) being assigned; i.e., as packaged beer [SO2] increases, beer flavor stability is claimed to increase (although consistent with Principles 5–7, this comes with a price to pay in terms of sulfury off-flavors!).

I cannot overstress to the reader the importance of paying strict attention to the exact wording used for the effect when first reviewing a fishbone. For example, interpreting a cause with a (+) symbol is entirely different when the effect is described as "process control for DMS" as opposed to "[DMS] packaged beer"! For the former wording, a cause with a (+) symbol means improved process control for DMS is facilitated by this cause. In the latter wording, however, a (+) symbol means the cause directionally increases levels of packaged beer DMS. In U.S. lagers, unlike many European lagers, the design goal is to decrease beer DMS levels. As such, a (+) with the latter wording is viewed by this author to be negative in terms of the ability to maintain process control.

"I get it now" quotes

As the fishbones grew in number and scope, I decided to periodically include quotes or statements striking a cord with me when first heard or read. Normally, these provided me with an "aha, I get it now" moment, enabling a better "gut-level" understanding of the effect under consideration. A typical example is the following quote from Dr. Bob Foster found on fishbone Xc, where the effect in this case is "predicting/correlating flavor stability":

"EPR" is a magnetic resonance technique that measures the transition of unpaired electrons in an applied magnetic field. Like a proton, the electron has "spin" called the magnetic moment. The magnetic moment makes the electron behave like a tiny magnet similar to the one you might put on your refrigerator. When an external magnetic field is applied, the paramagnetic electrons can either orient in a direction parallel or antiparallel to the direction of the magnetic field. In wort or beer, this "spin" is trapped with a nitrone compound when free radicals are formed producing a stable radical-spin adduct complex detectable by EPR. In wort and beer, there are sufficient supplies of antioxidants so that the radicals being formed are scavenged before the spin trap can react with them. When the natural antioxidants are used up, the spin adduct starts to form in large enough quantities to cause a dramatic increase in the EPR signal intensity. On a graph, the EPR signal shows a significant upward inflection and the "lag time" can be measured.

The motivation and need to include such "I get it now!" statements became more and more acute as the scope of the fishbones expanded beyond the comfort zone of effects pertinent to my academic training (i.e., high gravity brewing, yeast physiology, and chromosome fingerprinting). As this point was crossed very early in transitioning from an academic career to a brewing career, I have elected to include these statements in the hope they serve a comparable purpose for at least one reader.

Correlative relationships

In many cases, the relationship between an effect and a fishbone "cause" is only correlative, not cause and effect. For example, in the relationship between furfural and beer flavor stability, furfural itself is widely believed not to be a compound imparting stale beer flavors. Researchers, however, have observed an inverse correlation between furfural and beer flavor stability, with higher furfural levels at packaging correlating with decreased beer flavor stability (via the formation of staling compounds that do not include furfural). This example is reflected in the following quote from researchers at the Sapporo brewery in Japan found in fishbone Xh, "Predicting/Correlating Flavor Stability":

While furfural itself has a taste threshold far above levels generally present in beer, a correlation between increased furfural content and flavor deterioration with respect to oxidation, browning and papery flavor qualities is established.

Because furfural is much easier to assay in beer than the carbonyl compounds directly responsible for stale flavors, brewers can use furfural as a marker to assess the effectiveness of efforts intended to improve beer flavor stability without having to develop an in-house method for the actual staling compounds themselves.

Gauge-related references

Another category of information atypical for fishbones, but which is included nevertheless, pertains to methods of measurement for the effect under consideration. Examples include the plethora of assays used to assess yeast viability and vitality (e.g., IIIa–e), beer flavor stability (e.g., Xa–j), beer foam (e.g., XXVIi), beer physical stability (e.g., XXXIIg, i, and j), or beer filterability (XXXIf).

"Monty Python" content

In a few rare cases, several fishbones have content that can only be described as "and now, time for something completely different." As humor is subjective, I will leave it to the readers to identify, or assign, "Monty Python-like" designations as they see fit! I certainly know the content that struck my funny bone when I first came across the information. Many of these are not necessarily practical in nature but are included to add a little comic relief!

Red vs. black print

In an effort to make the fishbones as practical and actionable as possible, fishbone text is denoted in one of two different colors, red or black, with the distinction being anything in red is considered to be

  • a process variable over which an operator has direct control (for example: kettle evaporation rate (+) and DMS control; i.e., as kettle evaporation rates increase, process control over DMS also increases);
  • while certainly subjective, a particularly cool quote or observation;
  • just about anything to do with yeast!

Content in black print is considered to be more "theoretical" and informational in nature, not an observation that a process area operator could apply to troubleshoot process control issues.

"Comic Relief" content

As one might imagine, these fishbones can at times be somewhat droll and sleep-inducing. To overcome this, I have periodically included content that is somewhat esoteric in nature, with the hope it might lead to a refreshing chuckle, or groan, by the reader. For example, "kilning me softly with . . ." finds itself as a cell dealing with DMSP regulation in malting, as does "banning the tune Come Together" in the fishbone covering premature yeast flocculation (apologies to Roberta Flack and the Beatles, respectively). Please then when you come across these cells, interpret them as the wanderings of an old brewing scientist.

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