I'm putting together an "all glass" kit with two carboys and want to brew a DIPA but I'm a little concerned about temperature ranges where I'll be fermenting. I'm looking at somewhere between 15-18 Celsius. A friend told me that using an Ale yeast in that range will give the beer a bad flavor. I'm a little skeptical but realise anything is possible. With this being my first go I'd really like to nail it. Any insight is appreciated.
Cheers,
Ethan N.
Fermentation temperature does play a pretty big role in how the beer is going to taste. If the temperature is too high you can get excessive amounts of ester production and also can produce higher alcohols and phenolics that are undesired.
If the temperature is too low, ale yeast can be sluggish or go dormant too soon causing under attenuation. It can also fail to reabsorb byproducts from fermentation such as diacetyl. You would seem to be on the very low end of the fermentation range for ale yeast at 15-18C. This temperature range may work well with hybrid yeast such as Alt(wyeast 1007) or steam beer yeast(wyeast 2112).
An optimal range for most ales would be around 19-20C(66-68F).
Yes, yeast have an optimal temperature range.
They become dormant and won't ferment all of the sugars impacting the flavor, mouth feel and alcohol content
They flip out and produce fusel alcohols that can taste like cleaners or solvents. You can shake some of these flavors off during secondary but if there's too many they'll stick around. A Banana flavor in beer could be attributed to high esters during fermentation, diacetyls is another.
One more important point about temperature that isn't immediately obvious to newer brewers is that the ambient temperature of the room is NOT the temperature of the fermenting beer. Fermentation is an intense activity that produces a lot of heat, and the stronger the beer, the more heat is generated as the yeast go nuts eating all the sugars.
For a DIPA, I would expect that on day 2-3 of active fermentation, you'll see the temp of the fermenting beer be as much as 10 degrees Fahrenheit higher than the air temperature of the room the beer is in. And for an IPA-style brew, this higher temp can really make the beer taste wrong.
To combat this, get a big tub/drum/whatever to put the carboy/bucket in, along with a few gallons of water. Put frozen water bottles or ice packs in the water daily and keep an eye on the temps every 10-12 hours, especially during the first 5 days of fermentation or so. As fermentation slows down, the temperature will slowly drop back down to near ambient temps.
Of course, if you are starting the yeast off on the cool side of their preferred range, then maybe the rise in temps will just bring it up to the high end of their acceptable range, in which case everything is fine by itself. But just be prepared to act quickly if you see the temps go above the recommended high range.
This very strongly depends on which yeast you use; some yeasts throw pretty strong off-flavours if fermented warmer than their recommended range, others are extremely tolerant.
I have never heard of bad flavours coming from fermenting at a temperature lower than recommended. The only thing that a lower-than-recommended temperature can do, that I am aware of, is to ferment much slower and possibly even not at all.
Since you mention that this is your first go, I'll point out that the stronger styles of beer (and a Double IPA most definitely counts!) are much more challenging beers to make well. It will almost certainly be drinkable, will most likely be impressive, but it will be very difficult to make a strong beer that is great. Sooner or later I suggest you try making some straightforward 1.045-1.050 beers, while they don't sound nearly as interesting it is actually possible to make something incredibly good.
