Wanted vs unwanted off flavors (banana / pear)

[estebanuri]

My last two batches have unwanted banana off flavors.
Some info: 5 gals, OG > 1070, all grain barley malt. yeast S04 for the fist one, and T58 for the second.
I could not monitor the fermentation temperature.

According to what I read, these aromas are generated when the fermentation temperature is high.
My previous batches fermented without temperature control and had no problem, but now that the summer is approaching I think that investing in temperature control would be worth it.

On the other hand, some time ago I tasted a craft beer plenty of aromas of pears (or apples).
Later I bought it again, but this time I couldn't find those aromas at all. Then I thought that would be interesting to achieve those tasting notes on purpose, but how?

In short I wonder,
- What temperature ranges would you recommend to achieve (or to avoid) this banana off flavor?
- What temperature ranges would you recommend to achieve this pear/apple off flavor?
- What other factors (yeasts, time in bottle, mash...) could affect the generation of these esters?

Thanks in advance!

 

[Zver]

In short:
1. Ferment at lower side
2. Ferment at upper side
3. Yeast, pitch rate, aeration, OG.

Banana is isoamyl acetate, apple - acetaldehyde.

"Belgian yeasts typically produce more esters than British ale yeasts, and also some molecules associated with wheat yeasts. Logsdon adds, “Fusel alcohol raises perception of isoamyl acetate (banana). It isn’t detected as strongly when fusels are lower.” Higher original gravities, higher attenuation and inadequate aeration leads to more esters. (See the sidebar on page 45 for more.)

Increased fermentation temperature increases ethyl acetate levels, floral and fruity esters, and may be necessary for some of these yeasts to finish attenuating. Lower temperatures promote perception of phenols.

Higher pitching rates lower ethyl acetate levels. Very high or very low pitching rates increase ester levels.

Taming the beast begins with finding a balance. Defining balance can be another matter.

Consider Logsdon back on the subject of pitching rates. “Boosting the (pitching) rate reduces esters and creates more acetaldehyde (which have a green apple character). Reducing aeration increases esters,” he said."

https://byo.com/body/item/636-fermenting-belgian-style-beers