exBEERiment | Real Wort vs. Dextrose Yeast Starter In An American Amber Ale

Author: Greg Foster

 “Yeast that has been eating sucrose, glucose/dextrose, or fructose will quit making the
enzyme that allows it to eat maltose- the main sugar of brewer’s wort.”
~From How to Brew by John Palmer~

Yeast starters have been discussed ad nauseum in brewing books, blogs, and forums, as they’re considered to be one of the most important building blocks in the production of good beer. The number of yeast starter how-to’s (ahem) one can find with a simple Google search is a testament to their importance, and while methods may differ in some ways, they all agree on one major point:

Brewer’s wort must be used to make starters.

According to experts, yeast quickly begin to lose the ability to consume maltose if they aren’t propagated in a maltose-rich environment– dextrose (corn sugar) and sucrose (table sugar) are strictly forbidden as starter medium. Homebrewers have readily accepted this advice, present company included, though lately I’ve wondered how big of a deal the type of sugar in my starter really is. Is it possible the lab grown, highly viable yeast we use is healthy enough to adequately ferment a maltose based beer after chomping through a relatively small volume of low gravity dextrose wort?

I knew what I had to do.

| PURPOSE |

To investigate the potential differences between beers made from the same wort and fermented with yeast propagated in either a dextrose starter or a real wort starter.

| METHODS |

This xBmt began a few days before brewing with the making of yeast starters. For the real wort starter, I used 1.8L of wort made from a 100% 2-row mash I’d previously canned, while the dextrose starter was produced by combining pure corn sugar with RO water until it achieved a similar SG.

According to those who know more than me, a problem with using dextrose for yeast propagation is that it doesn’t contain the nutrients required for healthy fermentation, hence I added a fairly sizable amount of nutrient to that starter to give the beer it’d be pitched into a fighting chance; the real wort starter was dosed with a standard amount of the same nutrient then both were boiled for equal lengths before being chilled.

I confirmed the OG of the 2 starters were in the same ballpark.

It was time to pitch the yeast! I lucked out by grabbing a 15 day old WLP090 San Diego Super Yeast, so I split this ridiculously fresh vial equally between the starters and got them spinning on my stir plates.

I also followed another tidbit of advice from John Palmer:

If you make your starter using a malt extract that includes refined sugar, it is better to wait until the yeast have finished fermenting and settled out before pitching to the main wort.

Since one of my starters was 100% corn sugar, I allowed both to completely finish fermenting before pitching into actual wort. After reading about a similar experiment performed by Kai Troester, I expected the dextrose starter to take longer to finish than the real wort starter, though I was unsure how much longer. In typical fashion, the real wort starter took less than 2 days to fully ferment out, while the dextrose starter took a solid 5 days, which might be reason enough not to switch to this method of making starters. At this point, the real wort starter had a visibly larger yeast cake, though I reasoned this was possibly a function of the trub produced as a result of proteins in the wort, which isn’t present in dextrose. Ultimately, without testing it under a microscope, it’s impossible to say which starter produced more yeast.

Hydrometer measurements revealed the real wort starter dropped to a respectable 1.003 SG while the dextrose starter finished at an incredibly dry .996 SG.

Out of curiosity, I sampled the fermented liquid from the starters only to make the groundbreaking discovery that the dextrose batch tasted like mildly alcoholic and not terribly tasty water. It was time to make some beer.

As my planned brew day arrived, tragedy struck– I got the flu.  My next opportunity to brew wouldn’t come for another 10 days, my lonely starters left sitting in the corner of my warm room waiting to be used. I figured the additional 1.5 weeks at room temperature wouldn’t hurt the yeast, though it probably wasn’t helping either. With illness gone and recipe designed, I forged ahead!

DARK AMBER ALE

Fermentables

Hops

Yeast

I performed a standard 1 hour mash, hitting both my target mash temp and pH, which is always encouraging. Once complete, I collected the sweet wort, boiled and added hops, then chilled it to my target pitching temp. I decanted both starters before dumping the contents into their respective primary fermentation kegs. After hitting both fermentors with 60 seconds of pure O2, they were placed in my fermentation chamber set to 66°F. Then I waited… and waited… and waited. An entire 70 hours had gone by and not a single sign of fermentation activity from either keg. Had the yeast died? I haven’t had a batch take this long to start in a long time. I opened each keg to look for signs of infection, but everything looked fine, just lifeless. I kept on waiting.

Finally, 85 hours later, the real wort starter batch began to show signs of life; the dextrose starter batch wasn’t active until about 95 hours post-pitch, the longest fermentation lag I’ve ever witnessed. I let the beers ferment for another 4 days before taking an initial hydrometer reading.

The real wort starter batch was off to a strong lead at 1.020 SG while the dextrose starter beer had only dropped to 1.030 SG. I left them alone for another week until there were no observable signs of fermentation activity.

The real wort starter beer was at 1.014 SG, only .001 shy of my target FG. The dextrose starter batch, on the other hand, was sitting at 1.020 SG, which sucks, but even worse, it emanated a strong, unmistakable aroma of… BBQ sauce? Very odd and not at all promising. I wasn’t about to throw in the towel on this xBmt, so I gently shook both fermentors to re-suspend the yeast and ramped the chamber temp to 68°F for 2 days before taking another hydrometer measurement.

Back in business! The beer pitched with the dextrose starter dropped to 1.017 SG and continued to bubble very, very slowly for another 5 days while the real wort starter beer appeared to do nothing. Finally, the 4th hydrometer reading showed both beers to be at a similar SG of 1.013.

For those keeping score, that’s 23 days it took for the dextrose starter batch to reach target FG. My word. With fermentation complete, I cold crashed the beers for 2 days, fined with gelatin, then kegged them up and let them force carb over the next week.

| RESULTS |

Twenty-two adventurous volunteers  from the Pacific Gravity Homebrew Club kindly agreed to take part in this xBmt, a panel comprised of a solid mix of experienced homebrewers, BJCP judges, and general lovers of craft beer.

Each participant was blindly served 3 samples in identical opaque cups, 2 from the dextrose starter batch and 1 from the real wort starter beer, then asked to select the beer they thought was different.  Statistical significance would be reached if 11 of 22 (p<0.05) tasters were able to correctly identify the odd-beer-out. The final tally showed only 10 of 22 tasters (p=0.11) correctly selected the real wort starter beer as being different, 36% more than we might expect by random chance alone, though still not enough to establish statistical significance.

Interestingly, all 4 BJCP judges who participated selected correctly, 2 of them even mentioning this was the easiest triangle test they’ve done.

Additional follow up questions were asked in the survey, but please keep in mind I’m revealing these results just for fun, as the fact the null hypothesis was not rejected implies this data holds little if any scientific value.

Following the initial triangle test, participants were asked to describe what differences they perceived in the sample they selected.  Answers varied greatly among those who selected correctly on the triangle test with a couple tasters describing the real wort starter beer as more bitter, while others perceived it as maltier, under-attenuated, “olive smelling,” and more phenolic.

In terms of overall preference, responses were pretty evenly split with 3 tasters choosing the real wort starter beer, 4 preferring the dextrose starter beer, and another 3 endorsing no preference.

After the nature of the xBmt was revealed, participants were asked to guess which beer they thought was fermented with a dextrose starter.  Three guessed correctly, 2 were wrong, and the most popular response, “I have no clue,” was selected by 5 tasters.

Throughout this xBmt, I was convinced statistical significance would be established. The dextrose starter beer took an eternity to finish fermentation and the gravity samples I took smelled distinctly odd.  There was no way these 2 beers were not going to be obviously different. When the beers were ready for tasting, my certainty solidified, as they didn’t even look the same.

The real wort starter beer was darker, clearer, and easily the more pleasant looking, while the dextrose starter batch was a cloudy, unappealing mess.  Given the incredibly obvious visual differences, I literally had to blind myself when it finally came time for me to taste these beers.

My Impressions: I was rather surprised during my initial attempt at the triangle test– I couldn’t immediately tell a difference.  I perceived the beers as being far more similar than I expected. I took a few big gulps from each of the cups, consuming much more than the typical xBmt participant, and eventually noticed a subtle difference in the finish. The wort starter batch seemed to have a cleaner and perhaps slightly more bitter finish. I correctly selected the odd-beer-out. To prove my choice wasn’t random, I did a few more side-by-side tests and got those right as well.  Apparently, I could perceive a difference, but it was admittedly far more subtle than I expected.

| DISCUSSION |

Despite the lack of significant results, this xBmt made it clear to me that the advice against using a dextrose starter is more than just urban legend. By most observable metrics, it seriously under-performed and did not contribute anything of value to the brew day or resultant beer. Consider the following observations:

• The dextrose starter took 2.5 times longer than the real wort starter to fully ferment out.
• Once pitched, the dextrose starter batch took 10 hours longer for fermentation activity to appear.
• The dextrose starter batch took an agonizingly long 3 weeks to reach FG.
• The dextrose starter beer was cloudier and far less visually appealing than the real wort starter beer.

Even if the finished beers were characteristically exactly the same, I see no reason to recommend making a starter using 100% dextrose. Real wort produced from mashed grains or malt extract just seems to work better–  it’s faster to start, quicker to finish, and doesn’t smell like a freshly opened a bottle of KC Masterpiece. Of course, this is just a single data point and, as we often do, I strongly discourage anyone from taking too much stock in the results of this fairly highly controlled xBmt. Wanna try fermenting a beer with a starter made from corn sugar or apple juice or regular old table sugar? Be my guest, after all, it is just beer and I wouldn’t want to dissuade your own personal experimentation.

But honestly, I’ve absolutely no intentions of using a dextrose starter to make beer ever again. Cheers!

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| Read More |

18 Ideas to Help Simplify Your Brew Day
 7 Considerations for Making Better Homebrew
 List of completed exBEERiments 
 How-to: Harvest yeast from starters
How-to: Make a lager in less than a month 

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