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I recently brewed an oatmeal cream stout from the Mashmaker book (recipe here https://growlermag.com/homebrew-recipe-oatmeal-cream-double-stout/) with the intention of adding some chocolate & hazelnut flavours.

Main difference initially is that I added some cacao nibs to the mash.

I hit the OG, however the FG has come out at 1.032, rather than the expected ~1.015...

I had read the yeast I was using is highly flocculant, so I pitched some more after 2 weeks, to no avail. Fermentation schedule looked like -

  • Day 0 - 18C, pitched 1 smackpack 1318 London 3 yeast
  • Day 6 - 21C, roused yeast, gravity 1.032
  • Day 13 - 21C, still 1.032, added 1 pack dry Garvin/Nottingham yeast
  • Day 17 - still 1.032

For completeness, I scaled this down to an 11L brew:

  • Maris otter 2240g
  • Flaked Oats 263g
  • Roasted malt (blackprinz) 230g
  • Pale Chocolate 209g
  • Crystal 120 (Dark Crystal) 164g

  • Lactose 263g

  • Nugget @ 60min 16g

  • Cacao nibs (mash) 49g

  • Cacao nibs (secondary) 98g

Any thoughts on what might have gone wrong here - could the cacao nibs have somehow impacted the amount of fermentable sugers in the mash? (or are my sums just off..?)

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    what was your mash temp? I had something similar, and had mashed way to high and ended aith 1.040 F.G.
    – jsolarski
    Commented Nov 17, 2018 at 18:23
  • Mashed at 68C, for 90mins
    – RYFN
    Commented Nov 18, 2018 at 9:59

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No. I'm not aware of cacao nibs having any enzyme inhibiting abilities.

Either something else caused a less fermentable wort. Ie higher temp or low beta-amylase in malt.

Or, something caused yeast to give up on an otherwise fermentable wort. Stress, low nutrients, low oxygen, low pitch etc.

Edit: looking closer at the recipe I would NOT put a 1.015 target on it. Much closer to 1.030. I believe you are at terminal gravity with 1.032. About 50-75% of your sugars from the specialty grains will not ferment. 100% of the Lactos will not ferment.

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  • Thanks! So it's pretty unlikely this recipe would have hit 7 or 8% regardless? The FG there I calculated based on the OG and expected final ABV.
    – RYFN
    Commented Nov 18, 2018 at 10:01
  • Only a prgram like beersmith will properly guess a FG and take into concideration unfermentable sugars based on mash process, grain type, sugar type.
    – Evil Zymurgist
    Commented Nov 18, 2018 at 21:45

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