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I am looking to reproduce an incredible fruity aroma and flavour from a recipe I made a year ago. Looking at the recipe I am guessing it may be from the yeast.

3lb 2row
1lb Rye
.13oz nugget @ 60 min
.1oz Columbus @ 60min
.1oz Northern brewer at 30min
.3oz Northern Brewer @ flame out
WLP002 yeast straight from the vial.
Batch size: 2 gallons.

Assuming 2 gallon batch size...
(Calculated and not measured!)
OG: 1.055
FG: 1.014
ABV: 5.39%
IBU: 40.39
SRM: 4.11

Unfortunately this is all the info I have written down.

I remember sampling the beer at day five which had an incredible fruity aroma and taste. There was a ton of yeast in suspension, so much that the beer was completely cloudy. It was very orange and the taste was almost like ... orange juice. I swear I thought maybe someone went to my fermenter and poured a cup of tropicana in.

I have been trying to reproduce this "fruitiness" to no avail. I made this recipe at the time using an airlock and 18C fermentation temp. My latest two attempts are biased in the sense that:

  1. They have been fermented using 3 and 4th generation WLP002 very healthy yeast cakes. I am definitely over pitching.
  2. They have been fermented purely under pressure (20psi)

The result has been that the beer is very clean and ester free. There was virtually no difference in flavour using a temperature of 20C vs 24C (ambient) and certainly no fruitiness. I sampled these beers at around the same time at 5-7 days.

My most recent experiment involves a similar recipe but fermented under pressure after the first 9 hours, an OG of 1.090, and 24C (ambient) (gas was coming out of the blow off tube 20 minutes after pitching! The keg is quite warm to the touch so its probably more like 27C). I'm changing a little too many variables here, the pressure, the OG, and temp, but these are all to push the esters to the limit.

Has anybody ever gotten huge amounts of fruitiness from WLP002?

  • I should note that my experiment failed to reproduce any fruitiness... – fthinker Nov 11 '15 at 3:53
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You are doing two things (over-pitching and fermenting under pressure) that will drastically reduce the amount of ester production, which is primarily responsible for the fruitiness of beer.

Over-pitching reduces the extent of yeast growth, which is directly related to ester production. Basically the yeast can reproduce fewer times over, having started at a higher concentration, before they become limited by the amount of nutrients available. Less yeast growth almost always means less fruitiness.

Fermenting under pressure chiefly affects ester production by increasing dissolved CO2 levels in the fermenting beer, as the pressure itself has very little effect on the yeast's physiology. Dissolved CO2 is inversely related to ester production, so fermenting under no pressure would be the way to go for maximizing fruitiness.

"I'm changing a little too many variables here, the pressure, the OG, and temp, but these are all to push the esters to the limit. "

The higher OG and temperature should indeed help to push the fruitiness, but are probably being undone by over-pitching and pressure. If you're seeking the same flavors you got before, it's probably best to follow that procedure as closely as you can.

  • "Dissolved CO2 is inversely related to ester production" - that is very interesting, how does that work? – fthinker Aug 7 '15 at 16:18
  • It's not entirely understood, but increasing dissolved carbon dioxide seems to have an inhibitory effect on the formation of acetyl co-enzyme A, a key component of yeast metabolism and a direct precursor to some of the most prevalent esters. Here's the abstract of the paper from which I got this information. – Franklin P Combs Aug 7 '15 at 17:19
  • That's interesting. Looking here it seems that pressure can also have an inhibitory effect on yeast growth which could also explain the lack of esters. onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1992.tb01137.x/… – fthinker Aug 12 '15 at 19:51
  • Yes indeed it could. The study I linked to shows no connection whatsoever between dissolved CO2 and lowered yeast cell count or fermentation rate, so my guess would be that this is very strain-dependent. – Franklin P Combs Aug 13 '15 at 20:20

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