Tuesday, February 23, 2010

Fermentation experiment #1: Yeast quantity

As promised, I am still here, and focusing on my current passion- fermenting!

I have been a very amateur home brewer for several years now, mostly playing with extract kits.  I have started down the all grain road with some partial grain recipes recently, and hope to take the plunge soon (once the budget is there for a nice pot like this).  

One issue that has always bugged me was the haziness of fermenting recipes online.  Homebrewing has a pretty established online community with sound data and recipes, but once you enter into the big wide world of alternative brewing types, fruit wines, meads, and more, the recipes become rapidly more dubious.  Often it appears that someone found an old recipe, posted it online, and then every other recipe online looks suspiciously like the first one, with little thought as to whether the recipe really works.  

Well I decided to stop whining about it last month, and start doing some experimenting of my own.  My laboratory is my kitchen, and my tools primitive, so buyer beware: I will do my best to present sound experiments and data, but don't take my word for it- try it out yourself!

The first round of experiments will focus on the components involved in a very simple fermentation- how much yeast, yeast nutrient, and fermentable sugar results in a quick and tasty fermentation?  From there I can branch out to different yeast strains, types of fermentable sugar (plain sugar, grain, rice, grapes, etc..), temperatures and more.  

For now I will be measuring two main variables- one very quantitative (speed of fermentation), and one extremely qualitative (taste).

Finding the balance that maximizes these two variables across a range of conditions should allow my brewing to improve greatly, and hopefully provide some entertainment at the very least, if not useful info!  All right, here goes:

Experiment #1: Yeast Quantity

To determine how much yeast should be added for an ideal fermentation run.  (The basic rule in fermentation is keeping the engine of your madness happy- the yeast.  Stress the yeast and they ferment slowly, and produce nasty odors and flavors.  Yeast wants a certain temperature, certain nutrients, and the right concentration of sugar- just like Goldilocks, the yeast wants everything to be just right...)

5 1 gallon glass jugs
5 airlocks
5 rubber stoppers or bungs (drilled through)


  1. Boil 8 pounds of sugar with 2 gallons of water and 3 grams of citric acid for 10 minutes to invert the sugar (this is supposed to aid the yeast in fermenting the sugar- I will have to check this out in another experiment).
  2. Divide the inverted sugar water between the 5 cleaned and sanitized jugs (about 7 cups each for me).  
  3. Add cold water until about 1 cup from the top (to allow room for fermentation and bubbling) to each.
  4. Add the yeast nutrients (I added 1 teaspoon of yeast nutrient and 3/4 cup of Gerber barley baby food- weird I know, but it is chock full of nutrients yeast like...) to every jug.  
  5. At this point the water should be at a safe temperature to add the yeast (below about 110), but make sure or the yeast will all die if it is too hot!
  6. Add 1/2 teaspoon yeast to the first jug, 1 teaspoon to the second, 2 to the third,4 to the fourth, and 8 to the fifth. Bakers yeast is probably going to produce some interesting flavors, but two reasons motivated me to try it.  
    1. Baking yeast is super cheap ($4.50 for 2 pounds at Sam's club), just like me.  Beer yeast is expensive.
    2. Everyone says to never use bakers yeast because it will produce a terrible taste.  That motivated me to try it out for myself.
  7. Insert the airlocks into the stoppers, insert stoppers into the glass jugs (labeled 1-5) and swirl them to mix. 
  8. Measure the specific gravity (density) of each jug to make sure they are all the same.
  9. Let it ferment, checking the specific gravity every couple days to see how the fermentation is proceeding.
  10. I will consider the fermentation done for a jug when the specific gravity is at 1.000.  
  11. Once all jugs have finished fermenting, do the taste test.

Day zero (brew day): Within 15 minutes jug 5 (eight teaspoons yeast) was already bubbling away.  Within 1 hour there was some fermentation visible in all jugs, with a direct correlation between yeast quantity and rate of bubbling.  
Interesting- I thought I had added so much yeast to #5 that it wouldn't be any faster than #4.  Not so.

Day one: All are bubbling pretty well, but #5 is the fastest.  There is a visible color difference- #5 is the cloudiest, #1 is the clearest.

Day three:  I took my first hydrometer reading!  #1 has fermented only 12% of the sugar, #5 is most of the way done.  Wow, huge difference.  I will add a graph soon.  #5 is actually starting to slow down in fermentation, #4 is still full speed.  I wonder how stanky these will taste...