I have to admit this is one of my favorite subjects – beer! Recently I toured the Ellis Island Casino and Brewery in Las Vegas. Our guide stated that their customers loved “cold” beer. Like most of you I immediately thought of Six Sigma critical-to-quality (CTQ) trees. (Yes, this stuff can be a curse.)
As Lean Six Sigma practitioners we often hear words like “better, faster, cheaper” without anyone really understanding exactly what that means or how to achieve it. One of the primary duties Lean Six Sigma folks have is to convert abstract voice of the customer (VOC) requirements into a measurable output variable.
A CTQ tree is a Six Sigma tool used, in this example, to transform VOC (cold) into something measurable (temperature). The same can be accomplished with words like affordable, colorful, clean, and good on gas. So the question is what temperature constitutes “cold” for beer? Answer: about 47 degrees (acceptable range for ale beer is 44-52 degrees). So with random samples and a simple thermostat we can determine the amount of output variation and if our process is stable.
The way a cold beer gets to the customer is after the brewing process is complete the beer is stored at desired temperature in an insulated storage vat. At some future point (no more than two weeks at Ellis Island Brewery) beer is transferred to the casino bar via pipes that run across the roof – a very hot roof. The beer must remain at roughly 47 degrees during the transfer process; a pipe coolant system is used for this purpose. A bartender then pours beer into cold glass and hands it to me (yes, I spent a lot of time in the Gemba testing samples).
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Partial CTQ Tree
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| Customer Need | Drivers | CTQ Characteristics |
| Cold beer | Storage vat insulation | Beer stored at 47 degrees |
| Transfer pipe coolant system | Beer transferred from storage to tap at 47 degrees | |
| Bar refrigerator/freezer | Beer mug at 38 degrees | |
The key takeaway is that knowing the drivers that produce the VOC requirements helps you understand the systems that add value. Additionally, we better understand what we actually have control over (coolant systems and insulation), how those systems can fail, mitigate risk of failures and provide a good starting point if a defect occurs. Bottom line: it is useful in your quest for excellence. So the next time you hear abstract VOC requirements, think of cold beer and CTQ trees – I know I will.
