Go-ferm Pitch Rate Off-flavor Threshold: Inorganic

In the article on Tailored Additional of Nutrients with Go-ferm (TANG 2.0), I documented that adding Go-ferm at the recommended 1.25 grams per gram of dry yeast can quickly result in excess nutrients for session meads if the pitch rate is much above the recommended 1 gram per gallon of dry yeast. Then, in the high vs low pitch rate with Go-ferm triangle test experiment, it was found that a five gram per gallon pitch rate with the recommended amount of Go-ferm resulted in significant off-flavors when compared to a 1 gram per gallon pitch rate. However, this begged an important question: what is the pitch rate threshold for which Go-ferm off-flavors are perceived?

In this bench trial experiment, alternative amounts of Go-ferm and pitch rates were testing for their flavor and aroma contributions in a 4.5% ABV, carbonated, dry traditional mead fermented using S-04. Five Go-ferm amounts/ pitch rates were tested on identical musts. Each batch was fermented side-by-side and treated identically. Given the number of meads, all five meads were presented in a bench trials in front of two judges. Judges were asked to provided feedback and rank the meads.

Recipe: 4.5%, Dry Traditional Short Mead, April. 2021, 8 liter must, split into 1.7 liter batches

  • 7-liters of spring water
  • 1 kg of white honey, clover and alfalfa, from Peace Valley Apiaries
  • 0.5 g of cal. chloride
  • 0.25 g of gypsum
  • 0.2 g of Himalayan sea salt
  • S-04 yeast

Go-ferm variations:

  • 2.5 gram per gallon yeast pitch rate, no Go-ferm
  • 2.5 gram per gallon yeast pitch rate, 1.25 g/gal Go-ferm
  • 2.5 gram per gallon yeast pitch rate with 1.25 grams per gram yeast pitch rate of Go-ferm
  • 3.5 gram per gallon yeast pitch rate with 1.25 grams per gram yeast pitch rate of Go-ferm
  • 4.5 gram per gallon yeast pitch rate with 1.25 grams per gram yeast pitch rate of Go-ferm

Nutrients (calculated using The MeadMakr BatchBuildr):

  • YAN Recommended: 57.7-low; 78.3 – medium, 108.7- high
  • Medium-low YAN level provided excluding Go-ferm
    • Fermaid-K: 0.56 grams/ gallon (15.8 ppm YAN)
    • DAP: 1.02 grams/ gallon (61.2 ppm YAN)
    • Total ppm YAN from DAP and K = 77
  • Regimes
    1. No Go-ferm: 0 additional, 77 ppm YAN total
    2. 1.25 g/gal Go-ferm: 39.7 additional, 116.7 ppm YAN total
    3. 2.5-gram pitch w Go-ferm: 103 additional, 180 ppm YAN total
    4. 3.5-gram pitch w Go-ferm: 180.25 additional, 257.25 ppm YAN total
    5. 4.5-gram pitch w Go-ferm: 231.75 additional, 308.75 ppm YAN total

Notice how quickly the ppm YAN provided increases when you increase the pitch rate and are still providing the 1.25 grams of Go-ferm per gram of dry yeast, also graph above. While Scott Labs handbooks recommend providing a higher level of YAN when the pitch rate increases we can see that even at the 2.5 grams per gallon pitch rate the total YAN is already 180 ppm YAN, higher than even the high nutrient requirement. The pitch rate of 2.5 grams per gallon is the mid-range of the 2-3 grams recommended by the yeast manufacture, so such a pitch rate for dry ale yeast is warranted. Moreover, at the 2.5 gram per gallon pitch rate, The MeadMakr BatchBuildr does already warn of excess nutrients off-flavors from an equivalent amount of Fermaid-O.

Specs at time 0:

  • Target OG: 1.035
  • pH 7.00

At pitch

  • Mixed honey, water, salts
  • Transferred to fermentors, added needed Goferm.
  • Shook jugs for two minutes
  • Sprinkled yeast on top of must
  • First nutrient addition at 3 hours

Fermentation Notes

The inorganic nutrients were split into four additions and given at 3, 18, 36 and 48 hours.

Regular temperature, pH, gravity and aroma tests were taken. The table below summarizes the observations.

Time  2.5 g pitch, no go-ferm2.5 g pitch, 1.25 g/gal go-ferm2.5-gram pitch rate w go-ferm3.5-gram pitch rate w go-ferm4.5-gram pitch rate w go-ferm
+24h am 63.7°F pm 63.1°FUnfermented honeyUnfermented honeyUnfermented honeyUnfermented honeyUnfermented honey/yeast
+48h am 63.5°F pm 65.2°FSlight phenolic/ mothball honey
1.023
3.85 pH
Clean, honey, muddled apple 1.024
3.90 pH
Clean, honey, yeasty
1.022
3.93 pH
Yeasty
1.019
3.74 pH
Yeasty
1.019
3.93 pH
+3d
am 65.8°F pm 64.9°F
Clean, honey, muddled apple 1.013
3.39 pH
Clean, honey, bright apple 1.013
3.38 pH
Clean, honey, apple, yeasty 1.009
3.43 pH
Clean, honey, muddled apple, slight yeasty, slight alcohol
1.006
3.40 pH
Apple, slight go-ferm, slight alcohol
1. 006
3.56 pH
+4d
am 63.9°F pm 67.4°F
Clean, bright apple
1.006
3.24 pH
Pear, slight alcohol
1.008
3.35 pH
Pear, slight alcohol
1.005
3.38 pH
Pear, clean, yeasty 1.002
3.39 pH
Low pear, go-ferm,
1.002
3.53 pH
+5d
pm 65.8°F
Apple, honey, clean
1.003
3.32 pH
Pear, slight alcohol,
1.003
3.32 pH
Pear/apple, alcohol,
1.002
3.38 pH
Pear, honey, clean, 0.999
3.44 pH
Pear, alcohol 0.999
3.53 pH
+7d
am 66.2°F pm 67.3°F
Apple, clean 1.002
3.30 pH
Apple/pear, slight alc
1.002
3.32 pH
Pear, clean 1.000
3.38 pH
  
+8d
pm 67.7°F
Apple, honey, clean
0.999
3.32 pH
Apple, honey, clean
0.999
3.32 pH
Apple, honey, clean, alcohol 0.999
3.40 pH
  

Comments on Fementation

I really got my nose in during the fermentation to smell for aroma. Interesting, no Go-ferm had some phenolics at day 2, but it quickly cleaned up. The 1.25 g/gal Go-ferm has pretty clean aroma descriptors throughout, whereas the higher pitch rates did have yeastiness described at some point. The 3.5 and 4.5 pitch rates finished fermentation on day 5 but the lower pitch rates/ Go-ferm finished on day 8. I am a bit surprised that the first three finished at the same time.

Secondary

  • Most meads had dropped clear so transferred directly from primary to bottling
  • Carbonated with 3.6 grams/ 500ml of clover honey

Tasting Notes

Meads were tested at 4 months. Judges were blind to the treatment, and the meads were served all at once in random order in identical looking cups.

Judges were asked to provide brief tasting notes and rank from best to worst.

Time  2.5 g pitch, no go-ferm2.5 g pitch, 1.25 g/gal go-ferm2.5-gram pitch rate w go-ferm3.5-gram pitch rate w go-ferm4.5-gram pitch rate w go-ferm
Judge 1Clean, apple, slightly lager-like   Ranked 2nd Apple, clean  

Ranked 1st
Apple, clean, slightly bitter   Ranked 3rdTart, yeasty, bitter  
Ranked 4th
Tart, bitter, Umami   Ranked 5th
Judge 2Flat, not tart   Ranked 3rdBalanced, neutral  
Ranked 1st
Balanced, neutral  
Ranked 2nd
Yeasty, tart   Ranked 4thReally yeasty, tart  
Ranked 5th

Both judges ranked the 1.25 g/gal Go-ferm first in preference. This amount is consistent with the Scott Labs 1 gram per gallon pitch rate recommendation at this ABV level for wine yeasts. Judges were split between the no Go-ferm and the 2.5 gram pitch rate with the recommended amount of Go-ferm. The first judge thought the no Go-ferm was slightly better then the 2.5 gram pitch rate with the recommended amount of Go-ferm, whereas the other judge ranked those two in reverse order. The mead without the Go-ferm was also described as flat and being slightly lager like, which I interpret as a very slight sulfur character. The 3.5 and 4.5 grams per gallon pitch rate was described as bitter, yeasty, and umami flavors. Bitterness was also described for the 2.5 gram pitch rate with the recommended amount of Go-ferm by one Judge. Interestingly, tartness was described for the high pitch rates despite them finishing at a higher pH. I wonder if the meads picked up souring bacteria because of high residual YAN. It would be interesting to test the YAN and organisms hypothesis in a lab.


Final Notes

In the high vs low pitch rate with Go-ferm experiment, it was found that a five gram per gallon pitch rate with the recommended amount of Go-ferm resulted in significant off-flavors when compared to a 1 gram per gallon pitch rate. Here, the evidence suggests that the pitch rate threshold for the off-flavor occurred at pitch rates above 2.5 grams per gallon.

A couple of things I would do differently next time. First, I provided a medium level of YAN. However, another experiment showed that S-04 presented better with a low-level of compared to a high level of nutrients. I would like to try this again if it is found that a low nutrient requirement is also preferred to medium levels of YAN. Second, I gave four nutrient additions before 48 hours, and the experiment on nutrient timing that was done after showed that three additions are preferred to four.

Take away: for me, 1.25 g/gal Go-ferm showed preference over no Go-ferm and using the recommended amount for Go-ferm at normal ale yeast pitch rates and higher rates. It seems that at pitch rates above and maybe around 2.5 grams per gallon you can start to detect off-flavors from Go-ferm. Now, for my session meads recipes, I recommend adding 5 grams of Go-ferm in my 4 gallon batches.

These findings provide continued evidence that online calculators need to change. The MeadMakr BatchBuildr recommends rounding to 5 gram packets and adding 6.25 grams of Go-ferm per gallon for one gallon batches at this ABV level which is clearly inconsistent with recommendations and these findings. Moreover, allowing for high pitch rates and still recommending the standard amount of Go-ferm should probably come with a warning on Mead Made Right (current pitch rates range from 1-10 grams per gallon of dry yeast). Both of these websites are great, I use them and recommend them all the time, but there is still room for improvement.

To follow up, this experiment should be repeated with other yeasts, with fully organic nutrients, and at different ABV levels. My hypothesis for fully organic nutrients would be that the pitch rate threshold is even lower because Go-ferm already contains organic sources nutrients.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s