Slow/stuck fermentation with Windsor

[wedraper]

i brewed up a milk stout that i plan on mixing with cold-brewed coffee in the keg. i think i under-pitched the yeast, but i've not had that problem with dry yeast before. fermentation is in a converted fridge with a temperature controller. the ambient temperature dropped precipitously on day 3 and i don't have heat support in the chamber. the specifics are below:

Recipe: Bill's Coffee Milk Stout TYPE: Extract
Style: Oatmeal Stout
---RECIPE SPECIFICATIONS-----------------------------------------------
SRM: 45.0 SRM SRM RANGE: 22.0-40.0 SRM
IBU: 34.6 IBUs Tinseth IBU RANGE: 25.0-40.0 IBUs
OG: 1.071 SG OG RANGE: 1.048-1.065 SG
FG: 1.021 SG FG RANGE: 1.010-1.018 SG
BU:GU: 0.486 Calories: 235.0 kcal/12oz Est ABV: 6.6 %
EE%: 72.00 % Batch: 5.00 gal Boil: 6.70 gal BT: 60 Mins

---WATER CHEMISTRY ADDITIONS----------------


Total Grain Weight: 12 lbs 12.0 oz Total Hops: 1.70 oz oz.
---MASH/STEEP PROCESS------MASH PH:5.40 ------
>>>>>>>>>>-ADD WATER CHEMICALS BEFORE GRAINS!!<<<<<<<

Amt Name Type # %/IBU
1 lbs Chocolate Malt (350.0 SRM) Grain 1 7.8 %
1 lbs Oats, Flaked (1.0 SRM) Grain 2 7.8 %
8.0 oz Cara-Pils/Dextrine (2.0 SRM) Grain 3 3.9 %
8.0 oz Caramel/Crystal Malt -120L (120.0 SRM) Grain 4 3.9 %
8.0 oz Roasted Barley (300.0 SRM) Grain 5 3.9 %
4.0 oz Black (Patent) Malt (500.0 SRM) Grain 6 2.0 %


---BOIL PROCESS-----------------------------
Est Pre_Boil Gravity: 1.053 SG Est OG: 1.071 SG
Amt Name Type # %/IBU
2 lbs Extra Light Dry Extract [Boil for 60 min Dry Extract 7 15.7 %
1.00 oz Willamette [4.70 %] - Boil 60.0 min Hop 8 17.3 IBUs
0.70 oz Willamette [4.70 %] - Boil 30.0 min Hop 9 9.3 IBUs
6 lbs Maris Otter liquid extract [Boil for 15 Extract 10 47.1 %
1.00 Items Wort chiller (Boil 15.0 mins) Other 11 -
1 lbs Milk Sugar (Lactose) [Boil for 15 min](0 Sugar 12 7.8 %
0.50 tsp Irish Moss (Boil 10.0 mins) Fining 13 -



---NOTES------------------------------------
3/20/15:
- Steep in 5g, starting at 160F, stir occasionally, ending temp 144F
- Place grain bag on strainer, rinse with 1.7g room temp water
- Pour cooled wort through strainer into fermenter
- OG: 1.070/18 Brix
- Pitched 1pkg Windsor yeast dry at 78F
- 3/21: Active fermentation @12h, no fermometer, chamber at 63F; had to put on blow-off tube later in the day
- 3/24: SG- 12.5 Brix/1.037 (calculated)
- 3/29: SG- 1.036 (measured)/12.5 Brix; agitated fermentor, chamber at 54
- 3/30: SG- 1.036 (measured), rehydrated new Windsor yeast pkg and pitched
- 4/1: No surface activity

 

[JKaranka]

I stir / agitate Windsor, but even so it has fairly lousy attenuation.

 

[flars]

What was the temperature of the beer over this time period?

 

[wedraper]

All my thermometers were taken so I'm not sure. I'd bet mid to high 60s given chamber temp

 

[Yooper]

Windsor is notably low attenuating- but you checked the FG with a hydrometer, and not just a refractometer right?

 

[wedraper]

Yes I did for the ones denoted as "measured"

 

[Yooper]

Yes I did for the ones denoted as "measured"

Just checking!

I think there are several things going on here. One is that Windsor is notoriously low attenuating, and you got even lower- less than 50% if my quick math and 1.071 to 1.035 is correct. But about 9 points of that is lactose- which doesn't ferment, so keep that in mind.

Much extract is less fermentable than if you had mashed the grain, so there is that. Also, if you steeped what grain you had at 160, that would be less fermentable as well. (Actually nonfermentable, since the oats would only contribute starch and not fermentable sugar if not mashed with base malt).

In other words, between the low attenuating yeast, the high percentage of non-fermentables, and the combination, this seems to be where it will stay. I don't know if a more highly attenuating yeast will help at this point, but the added windsor yeast certainly would not, sorry.

 

[wedraper]

Thanks for the help. I think I'm going to pitch some S-04 and see what happens