All Grain, sticking fermentation. Suspect Malt?

[pjbiker]

Hi folks,

I've been all grain brewing for a couple of years now and can generally expect my beers to ferment down to at least 1.012 from 1.052 or thereabouts. I've used a variety of yeasts but currently use Danstar Nottingham for convenience. The last 3 brews have suffered poor attenuation which I couldn't quite explain. I thought it may have been too high a mash temperature but have been careful and the most recent brew looks like it may be going the same way as others, sticking at around 16-17. It suggests a high proportion of unfermentable sugars.

It occurred to me that it could be the Malt? Anyone else had this problem? I've only really had it before back when I used liquid malt extracts a few times. Can it be poor malting? I'm getting pretty much the same extraction as I always do 75-80% overall efficiency depending on how slowly I sparge. The Malt I have is 'Warminster' Maris Otter bought by the 25Kg sack crushed. I've used it before and its been OK.

 

[evanvine]

The Malt I have is 'Warminster' Maris Otter bought by the 25Kg sack crushed. I've used it before and its been OK.

This may sound stupid, But are you refering to a previous 25kg sack or earlier brews from this sack?

 

[unclepumble]

Poor attenuation is most likely lack of dissolved oxygen when pitching, try spraying the wort into the fermenter, and giving it a vigorous stir as well.

It could also be your water profile, but less likely

I would Try getting more oxygen in & try to add a yeast nutrient, zinc is best if you can source some (not easy). otherwise old yeast chucked in the last 5mins of the boil will help.

UP

 

[pjbiker]

The Malt I have is 'Warminster' Maris Otter bought by the 25Kg sack crushed. I've used it before and its been OK.

This may sound stupid, But are you refering to a previous 25kg sack or earlier brews from this sack?

Problem only with the current 25kg sack

 

[prolix]

it could be slack malt , old crushed malt that has enzyme difficiency. you would need to do a starch test at the end of the mash to find out. the iodine will go purple if starch is present.

get a new sack of malt and see what happens.

on side note have you bottled ant of these brews? because yeast can ferment big sugars it just takes time and those bottles could turn into gushers or worse bottle bombs

 

[robsan77]

I agree, the main reasons I have seen stuck ferments is unstable fermentation temps. With the cold weather recently this is particularly common unless you use a heated environment with a thermostat. Yeast doesnt like overnight cold temps, it can manage earlier in fermentation as its own heat generated keeps it warm.

 

[evanvine]

+1 Rob!
Ignore my earlier question, I was on the wrong track.

 

[pjbiker]

Been checking my records again. I've had high finishing gravities for the last 3 brews including one from a previous sack of malt (also Warminster). But, I did break a thermometer and used a new one around the same time. I generally aim for 65 C starting mash temp and records show I've achieved that or thereabouts. I considered pH which I normally manage by adding a pre-determined amount of CRS which I experimented with ages ago. However, once, 5 brews ago, I had no CRS and brewed without it, still obtaining 1.011 FG from 1.043 OG and 80% efficiency.

Conclusion so far, the malt is probably OK isn't it, so I'll mash at a lower temperature next time and maybe get a different thermometer to calibrate. Perhaps it was the old thermometer that was wrong? I'll re-post here after the next brew.

Brew #30 Mash temp 65.5C, OG 46, FG 20
Brew #31 Mash temp 63.5C, OG 51, FG 15
Brew #32 Mash temp 65C, OG 52, FG 18


@prolix I've got the odd bottle saved, no explosions yet but I'll bear it in mind :drink:

 

[evanvine]

Will be very interested to hear your results, good luck :thumb:

 

[pjbiker]

Brew #30 Mash temp 65.5C, OG 46, FG 20
Brew #31 Mash temp 63.5C, OG 51, FG 15
Brew #32 Mash temp 65C, OG 52, FG 18

Brew #33 Mash temp 63.5C Using a new thermometer! , OG 55, G 13 after 5 days so may fall further. think I've cracked it! :thumb:

Brew #33 Mash temp 63.5C Using a new thermometer! , OG 55, G 12 after 6 days