Understanding attenuation

[Chalkyt]

This is prompted by a recent post regarding WLP773. I used this yeast last year and the cider eventually went from 1.050 to 1.002 which suggests that it attenuated 96% even though it is supposed to be 80%.

Clearly I don't understand attenuation so can someone give me the "short course".

My understanding is that attenuation is a measure of how much sugar is consumed by the yeasts. So, in simple terms I would expect something such as WLP773 with an attenuation of 80% to stop an OG of 1.050 at FG 1.010, so why does it keep going.

Other popular yeasts such as SO4, Nottingham, etc have published attenuations in the range 70-80% so I would expect FGs from these to end up at around 1.010-1.012 which should leave a fair bit of apple flavour and sweetness as I understand that anything over 1.007 should have these characteristics and certainly that is the case when tasting.

But, typical FG always is a lot closer to 1.000 no matter what apple blends or yeasts I use, and that seems to be the case with everyone. After all, a FG in the 1.010-1.012 range would eliminate all the angst about adding artificial sweeteners, bottle pasteurising etc if an off-dry or slightly sweet cider is the target.

So it seems that practice doesn't line up with the theory... why is it so? Should a low attenuation yeast result in a more "appley" and sweet cider?

 

[dmtaylor]

The sugars in apple juice are considered very "simple" and nearly 100% fermentable by most yeasts. The most dry ciders with champagne yeast will finish at 0.992-0.994 specific gravity, because ethanol has a specific gravity lower than that of water at 1.000. The brick wall limit happens to be about 0.992. At that point is 100% real attenuation.

Meanwhile, ale yeasts are all rated based on their apparent attenuation, which measures as if the attenuation would hit its brick wall at 1.000, which for most intents and purposes, is pretty much true for all malt wort. The sugars in beer/ale/lager malt wort are much different and more complex than the simple sugars in apple juice. Maltose is a somewhat more complex sugar than glucose, fructose, or sucrose; and maltose makes up a high percentage of sugars in beer, and most yeasts can only provide apparent attenuation of approximately 75%, plus or minus a few percent. Hence a 1.050 wort will often finish at about 1.012 or thereabouts. And the real attenuation of the same wort is a bit lower, only 60% or something like that, since if you were to add extra enzymes and/or use a special diastaticus variant yeast, you might get the specific gravity down to about 1.000 -- can't even get it down to 0.992 like you can with cider. This limit of about 1.000 can happen with some saison yeasts with the diastaticus variant, which have the ability to consume maltotriose which is one of the most complex sugars in wort. I personally haven't seen a beer finish below 1.000 but if it were possible and the yeast could actually eat it all, perhaps it would be possible to get it down to 0.992, theoretically. Hence with wort the real attenuation is typically far from the same 100% that is possible with the simple sugars in cider.

Confused yet? I'm not exactly thinking straight at the moment so forgive me if I'm not making sense.

So anyway..... your example where the cider goes to 96% attenuation finishing at 1.002 is... actually very normal for cider, which is nearly 100% fermentable, and which if you have all the right conditions could get down to 0.992 or thereabouts if you had the simplest of sugars and a different yeast. But that 96% is still apparent attenuation. The real attenuation is lower, in the 80s or something.

And an ale yeast pitched into a cider should be expected to ferment much farther than the standard ale ratings because the sugars in apple juice/cider are so much more easily fermentable than wort. I've used ale yeasts before that have finished like 1.000-1.005 or thereabouts, which would NEVER get that low if the same yeast had been fermenting malt wort. Notty, US-05, S-04, others, I've used lots of different ones, all similar results, around 1.005 typically.

Wine yeasts on the other hand, typically will finish anywhere from 0.994-1.002 or so, maybe 0.997 average, something like that, if I let them ferment to dryness. I think WLP773 fits this category, i.e., a wine yeast with pretty average attenuation, pitched into an apple juice with very fermentable sugars, etc. EDIT: Oh wait... now I see that WLP773 is actually a blend of ale and wine yeasts. Huh. Well imagine that. I just read that AFTER writing what follows....

If your goal is a sweeter cider, you can play around with English and Scottish yeasts and see if you enjoy them. Personally I find ale yeasts to turn out a cider than tastes positively beery to me, and not so appley, not as appley as with good old Cote des Blancs white wine yeast, AND if I fiddle around with my process enough, I can get the CdB yeast to crap out early around 1.005 and preserve some of the natural sweetness, and in any case, it tastes WONDERFULLY appley with this yeast. And it's dirt cheap! I think I got 10 packs for $10 on Amazon, something like that. YMMV.

Ramble on!

 

[bmd2k1]

In short...yeast attenuation doesn't apply to cider. As long as the yeast doesn't reach its alcohol tolerance level...it will continue to rip thru the simple sugars in apple juice till they are all gone [emoji111]

 

[RPh_Guy]

In short...yeast attenuation doesn't apply to cider. As long as the yeast doesn't reach its alcohol tolerance level...it will continue to rip thru the simple sugars in apple juice till they are all gone [emoji111]

White labs claims 80% attenuation in apple juice.
https://www.whitelabs.com/yeast-bank/wlp773-scottish-cider-yeast-blend

But that 96% is still apparent attenuation. The real attenuation is lower, in the 80s or something.

Yes, the real attenuation is 77%.

(12.4 Brix to 2.8 true brix is 77% attenuation)

This is pretty misleading by White Labs in my opinion. There's nothing special about this yeast's attenuation, based on this result.

 

[Chalkyt]

Thank you for those replies. They answer a lot of questions. Like Maylar, I would have loved my WLP773 to have finished at 1.010 and couldn't really understand why it kept going.

It really does look as though attenuation has no real meaning when it domes to making cider so we will have to rely on something like stovetop pasteurisation to get a sweeter carbonated brew..

Hey Dave... what did you do to stop the CDB at 1.005. I am looking to try CDB this year (if I can get some, at this stage the only option is via ebay from USA at about $US10 each with postage).

 

[dmtaylor]

Hey Dave... what did you do to stop the CDB at 1.005. I am looking to try CDB this year (if I can get some, at this stage the only option is via ebay from USA at about $US10 each with postage).

Ack... Sorry, I lied, accidentally... I just checked my records and it fell to 1.001. I ferment cold in the low 50s, I rack early and often, and when gravity hits 1.010 or so, I keep it refrigerated, then let it sit in the fridge for another couple months until stable. Currently it's at 1.001 but potentially might lose a couple more points. But not to worry..... we can always cheat by adding xylitol to sweeten, which tastes exactly like sugar but is not fermentable.

 

[wasully]

good old Cote des Blancs white wine yeast, AND if I fiddle around with my process enough, I can get the CdB yeast to crap out early around 1.005 and preserve some of the natural sweetness, and in any case, it tastes WONDERFULLY appley with this yeast. And it's dirt cheap! I think I got 10 packs for $10 on Amazon, something like that. YMMV.

Ramble on!

What's the process?