How does yeast affect the taste of a beer?

Last Saturday as part of the American Homebrewers Association‘s Learn to Homebrew Day our club the Lake County Homebrewers set up our equipment at Guido’s Pizza in Kelseyville, CA to demonstrate and explain how to brew your own beer. (If you would like to start brewing your own but missed Learn to Homebrew Day see: From no brew to homebrew: Make your own beer in 3 simple steps)

The basic recipe was:
1/2 tsp   Gypsum (Calcium Sulfate)         (Mash 60.0 mins)
5 lbs         Pale Malt, Maris Otter (3.0 SRM)
4.1 lbs     Pale Malt (2 Row) US (2.0 SRM)
14.5 oz     Munich Malt (9.0 SRM)
7.3 oz     Caramel/Crystal Malt – 20L (20.0 SRM)
7.3 oz     Caramel/Crystal Malt – 60L (60.0 SRM)
7.3 oz     Melanoiden Malt (20.0 SRM)
0.47 oz     Columbus (Tomahawk) [14.00 %]     First Wort Hopped (FWH) 75.0 min
0.94 oz     Centennial [10.00 %]             Boil 20.0 min
1         Whirlfloc Tablet                 (Boil 15.0 mins)
1/2 tsp     Yeast Nutrient                 (Boil 15.0 mins)
1/2 tsp    Gypsum (Calcium Sulfate)         (Boil 15.0 mins)
0.91 oz     Simcoe [13.00 %]                 Boil 10.0 min
0.91 oz     Centennial [10.00 %]             Aroma Steep 1.0 min
0.91 oz     Simcoe [13.00 %]                 Aroma Steep 1.0 min

Est Original Gravity: 1.060 SG
Est Final Gravity: 1.013 SG
Estimated Alcohol by Vol: 6.1 %
Bitterness: 56.4 IBUs
Est Color: 9.5 SRM

Once the wort had been boiled and the hops added (along with the other stuff) we mixed all the batches together and then divvied it up to different members who would then add yeast to the wort (and begin the conversion to beer).

The wort up to just before the yeast is added will taste identical. To be sure, the water, hops, and malted barleys will all have contributed to the taste of the beer. Yet, the addition of the yeast will significantly change the taste of the final products.

Here is a list of the different yeasts that were added to the worts:

  • American Ale (Wyeast Labs #1056) [124.21 ml]
  • American Ale II (Wyeast Labs #1272) [124.21 ml]
  • Belgian Golden Ale (White Labs #WLP570) [35.49 ml]
  • Belgian Style Ale Yeast Blend (White Labs #WLP575) [35.49 ml]
  • London Ale III (Wyeast Labs #1318) [124.21 ml]
  • London Ale Yeast (Wyeast Labs #1028) [124.21 ml]
  • London ESB Ale (Wyeast Labs #1968) [124.21 ml]
  • San Francisco Lager (White Labs #WLP810) [35.49 ml]
  • Thames Valley Ale (Wyeast Labs #1275) [124.21 ml]
  • Brettanomyces Bruxellensis Trois (White Labs #WLP650 644) [50.28 ml] [Add to Secondary]

The first two American Ale yeasts are the “controls” and should produce the closest thing to a beer at a brewpub. I chose to try a California/San Francisco Lager yeast. Below is a quick video of how the yeast looks on the day after it was pitched (added).

This shows San Francisco lager yeast eating the sugars in the beer. As the Wyeast website describes this yeast as “particularly well suited for producing 19th century-style West Coast beers with woody/minty hop flavor. It retains lager characteristics at temperatures up to 65°F (18°C) and produces malty, brilliantly clear beers.” This beer is fermenting just a little out of the preferred temperature range. I may add a wet t-shirt to it to try to lower the heat.