Day 154

In Sensory Evaluation, we continued with tasting panels, specifically the various types of tests that you can perform with your panel, and why you would use each test.

For instance, suppose a brewery is adding a new production line, and wants to know if the beer produced by the new line tastes the same as the beer from the old production line. Or what if the brewery is thinking of changing their malt supplier but wants to know if the switch will change the taste of their beer noticeably?

One possibility is the “simple difference” test: a panelist is given two samples and asked if they are different. If they are different, how are they different? Because of the simplicity of the test, it is very accurate for detecting even small differences between two batches of beer.

In the “duo-trio” test, the panelist is presented with two unidentified glasses of beer; then the panelist is given another glass containing either the first or second beer and has to pair it with its twin.

In the “triangular” test, the panelist is given three glasses–again, two of one type and one of another–and asked to correctly identify the odd one. If the panelist correctly picks the right one, the tester can then ask what the difference is, and which beer the panelist prefers.

Then there are a variety of  “descriptive” tests to try to determine a beer’s various tastes components. For instance, you give 5-10 expert assessors a sample, and they write down descriptive term for the beer as well as the intensity of the various flavour components. From this you can create a flavour profile graph that accurately describes the beer.

Or perhaps you give your panelists four random samples and ask them to rank them in order of intensity of one of the tastes (say, bitterness , or perhaps an off-flavour like diacetyl.)

Then there is affective testing: finding out which beer is preferred. This can be a simple as providing two samples and asking which one is preferred. A more involved test asks the panelist to rank six beers from most preferred to least preferred.

A quick break for lunch and then on to Microbiology and a look at yeast: viability and vitality (i.e. is it alive and is it strong?), storing yeast, and propagating yeast–that is, growing a lot of yeast from a single petri dish colony. Then there’s washing yeast. Yep, like your car, yeast occasionally has to be washed. In the case of yeast, it’s because you’ve discovered that your yeast has a bacterial infection. Adding acid to the yeast slurry will kill the bacteria, but will also weaken your yeast, so this is something you don’t want to do unless necessary.

And then there is the calculation of how much yeast to add to your fermenter.
  1. First, look through your microscope (or use one of several other methods) to calculate both the number of yeast cells per mL in your slurry and the percentage of those that are viable.
  2. You want about a million yeast cells per mL of wort for every degree Plato, so calculate your pitching rate by multiplying your wort’s degrees Plato by a million.
  3. Multiply the volume of your wort by 1000 to convert from L to mL, and multiply the answer by your pitching rate from Step 2 to arrive at the total number of yeast cells you need.
  4. Divide the total number cells needed from Step 3 by (the total yeast cells per mL in your slurry times the percentage of viable cells from Step 1).

You now have the number of mL of yeast slurry needed.

It had been a long day, so I was thankful that Brewing Chemistry was largely a review of malt analysis and adjuncts that we had previously covered in Kevin Somerville’s first semester Ingredients class. Weekend time!

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