Fruit flavors from White Labs California Ale yeast I

The formation of fruity esters by a given yeast (i.e. not counting yeast genetics as a variable) is governed by many factors, some of which are conflicting can can drive you to drink. Some of these are:

• Pitching rate. Lower pitching rates (mainly in traditionally brewed ales) and higher pitching rates (in commercially brewed lagers) give you more fruity esters.
• Dissolved Oxygen (DO) levels. Lower levels of dissolved oxygen (ie less wort aeration) promote the formation of fruity esters.
• Fermenter geometry. A low, wide, flat bottomed fermenter will make it easy for the yeast at the bottom of the fermenter to vent off the CO2 produced. This is important, as CO2 inhibits the formation of fruity esters. A tall, narrow conical fermenter will retain more CO2 in the yeast deposit at the bottom, resulting in more CO2 inhibition and therefore lower levels of fruity esters.
• Pitching temperature. Fruity esters are formed from fatty acids and higher alcohols. More yeast growth early in the fermentation consumes more fatty acids early on, which leaves less of them available for ester formation later in the fermentation. Pitching cool delays yeast growth a little, which leaves more fatty esters available for subsequent ester formation.
• Fermentation temperature. Notwithstanding all of the above, this is the most important factor by far. Higher temperatures give you more fruity esters. The End. If you want to keep your fruity esters down, ferment cooler.

All of that said, many factors work against each other, and manipulating your pitching rate, aeration/oxygenation, pitching temperature and fermentation temperature schedule is always a trade-off.

So I would suggest you start by fermenting cooler. This will give you the biggest bang for your buck right off the bat. If that doesn't get you where you want to be, consider the other factors discussed above.

Note that yeast genetics also play an important role, so what works for one yeast may not work (or not work the same way) for another one. Belgian yeasts are well known for large amounts of fruity esters (e.g. Fermentis BE-256 goes nuclear on iso-amyl acetate / banana aromas) but typically respond far more to variations in DO levels. The difference between a well-aerated wort and a poorly aerated wort with BE-256 at the same temperature can be dramatic: the one can be a fruity ale and the other a 20 megaton banana bomb. An American ale yeast will most likely respond far more to temperature and pitching rate variations than it will to variations in DO levels.

Bottom line: experiment! :-)

23C/73F is at the top end of the range for this yeast(WP001) you have to take into account that during the most exponential growth of the yeast it can generate a fair amount of heat in the FV and may be pushing or at least maintaining the higher temp longer than you expect.

I would be trying to pitch in at around 68F/20C for a cleaner profile, the majority of the fruity esters are produced in the first 3 days of fermentation when the exponential growth phase is at its height.

It could also be that you are under pitching your yeast, thereby stressing it and causing the undesired flavours.

• What is your pitching rate? litres/g, usGal/oz?

It may even be six of one and half dozen of the other, as these effects can be additive.

Your fermentation temperature doesn't appear to be high enough to have that profile with such a clean yeast. You may look to a little longer boil time to drive away some of the potential off flavor producers. These can sometimes lurk on your palate as fruity. Some yeast food and oxygen in your next batch might increase fermentation and reduce any lag time you may be experiencing.