Racking the Riesling from the primary to secondary fermenter.Yeast can have a profound affect on the final flavor and aroma profiles of a wine or so we’re told. But how much of a difference is there really from one yeast to another? To answer this question I set up the Great Riesling Yeast Experiment.

In this experiment I set out to ferment one Riesling kit in two three gallon batches with two different yeast strains. To find out how I picked out my yeast strains read this.

This experiment, I hope, will answer the following more specific question.

  1. How much does a yeast affect the final taste and aroma of a wine?
  2. Can you make a more complex wine by fermenting the same grapes with two different yeasts and blending them back together?
  3. Is it possible to make good wine from a kit while not following the directions?


Yeast, as you know, is the star of the fermentation show. It is responsible for the creation of alcohol in wine, mead, and many other grown up beverages.

For a long time many winemakers did not believe that the yeast used to ferment grapes mattered much when it came to the final character of the wine. They believed that as long as the grape juice was fully fermented it all tasted the same.

It wasn’t until fairly recently that wine researchers started to study the effects different yeast strains can have. What they found was that it can make quite a big difference, however, they did say that it takes six months or so for that difference to show up.

Today, many winemakers do split fermentations for this reason. They ferment the same grapes with more than one strain of yeast in separate containers. Then they blend these wines back together to create complexities that neither yeast on their own could create.

The Yeast Experiment

Washington Riesling (World Vineyard)To answer the three questions posed above I set up the following experiment. I purchased a Winexpert World Vineyard Riesling (affiliate link) which makes six gallons of wine. To ferment this kit I selected RHST and W15 yeast strains based on their different aroma and flavor profiles (also affiliate links).

These two 3 gallon batches will be fermented and aged separately for a period of a few months. Once they’ve been made into complete and independent wines I will blend them back together in varying proportions.

Some bottles will contain 50% of each. Others will be blended at 25% one and 75% of the other. Lastly, I’ll bottle a couple bottles of each independently.

Now that we’ve covered the parameters of the experiment let’s talk about how it’s all going down. Currently I’ve got my wines in their secondary fermentation carboys, however, I’m going to cover the first steps in the experiment here.

Step 1: Inoculation

To get this experiment going I hydrated the grape juice concentrate in a six gallon fermenter per the instructions with the bentonite. Once the wine was properly mixed I started the yeast re-hydration process.

The kit instructions clearly state not to do this, however, as I’m not using the yeast that came in the kit I felt I needed to give the yeast the best possible chance of survival. It took only fifteen minutes to re-hydrate the dry yeasts separately.

While the yeast was hydrating I racked three of the six gallons of grape juice into a six gallon carboy for fermentation. Racking took a little longer than expected which made me nervous. For a few minutes there I was afraid that the yeast would be ready for inoculation before the racking was complete. Thankfully that didn’t happen.

Once the yeast was ready I added the W15 to the glass six gallon carboy and the RHST to the plastic primary fermenter. Next the airlocks were installed and the fermenters moved down to my fermentation lair (eh hem…basement).

Early Observations

As soon as the different yeast strains were hydrating you could already tell they would behave differently. The W15 immediately formed a frothy foam top and the smell wafted far and wide.

The RHST on the other hand was much more subdued. It didn’t froth up at all. It seemed to soften up but was largely still somewhat granular when I added it to the primary.

Inoculating both yeasts at the same time proved that W15 was a more active yeast. It started bubbling within a few hours and by nightfal was producing a steady stream of bubbles from the airlock. RHST took longer to get going and never reached the same fervor that the W15 did.

As for aroma the W15 Riesling smelled like a bold grape juice. On the other hand RHST produced a might lighter aroma and had more of a yeast aroma than anything else.

Check out Part II!