Yeast in high gravity & need to re-pitch

sweetcell · Mar 18, 2012

heya folks,

yesterday i brewed a 1.082 dark ale. unfortunately i fear that i over-heated my yeast before pitching, and that some of it might have been killed. i took my starter out of the fridge a little later than i intended to, and to speed up its warming i turned on my stir plate's heater. by the time i checked up on the yeast again it was very warm - i didn't take a temperature (i panicked and immediately put it in some cool water to bring the temp down), but i'm pretty sure that it was at an unhealthy temp for the poor yeasties. i'll do a test later with water and provide an estimate of that temp.

i pitched the starter once both it and the wort were cooled. 24 hours later and i have some fermentation going, so they didn't all die... but it's a rather subdued fermentation. i'm re-using this yeast (Wyeast Belgian Strong Ale 1388) and last time it took off really quickly. this slow start has me a bit concerned that i have too little 1388 in there and that the yeast will be stressed trying to digest all that sugar.

1) does yeast start slower in higher gravity worts? i would have thought that the extra sugar = faster and more vigorous fermentation.

2) i have some S04 dry yeast. should i consider adding it to provide backup to the under-pitched 1388? according to mr. malty i would need a pack and a half of dry, so if we estimate that the 1388 i have in there is about half a pack, throwing in the S04 might bring me up to a proper pitch count... is it too late to add? oxygen levels would be low since the 1388 had a 24 hour head-start.

Biobrewer · Mar 18, 2012

Stir plates can get very hot. One suggestion is to purchase a different stir plate. Ones that heat up like that are pretty cheap, and can do harm when they are on too long. Look into scientific ones like the ones from Corning. The magnet contains a fan under it driven by the same motor, which moves cooler air around the motor and magnet, cooling the plate and preventing hot spots.

So far as the starter you made, it may be ok. However, when things get that hot, you may not want to rapidly cool, as that will shock the yeast that are still living. I would say have some dry yeast on hand ready to hydrate. Take gravity readings every day for a couple days and see how the yeast are performing, then make a judgement call if they are performing well or if you need more yeast.

Biobrewer · Mar 18, 2012

Yeast do not necessarily start slower in high gravity, they just have a more stressful environment to deal with, which is why pitch rate is so important in high gravity beers.

Good luck!

Calder · Mar 18, 2012

The same amount of yeast in a high gravity beer (vs. a low gravity beer) will take longer to get going. It has more reproductions to do to get to an optimum quantity of yeast.

Adding S-04 now will not help. The Belgian yeast has consumed the O2 in the wort, so the S-04 will not reproduce. To get the right amount of S-04 yeast now, you would have to pitch 6+ packs.

I think you will find the Belgian is working fine, since you are seeing some signs of fermentation. If the yeast was stressed (low pitch rate) it can throw off some esters (but sometimes that is looked for in a Belgian and people deliberatly under-pitch). The only advice I would give is to try and ensure you keep fermentation temps in check to prevent too many esters and fusels.

sweetcell · Mar 18, 2012

Biobrewer said:
Stir plates can get very hot. One suggestion is to purchase a different stir plate. Ones that heat up like that are pretty cheap, and can do harm when they are on too long. Look into scientific ones like the ones from Corning. The magnet contains a fan under it driven by the same motor, which moves cooler air around the motor and magnet, cooling the plate and preventing hot spots.

So far as the starter you made, it may be ok. However, when things get that hot, you may not want to rapidly cool, as that will shock the yeast that are still living. I would say have some dry yeast on hand ready to hydrate. Take gravity readings every day for a couple days and see how the yeast are performing, then make a judgement call if they are performing well or if you need more yeast.

my stir-plate is a "scientific" one and the heat was from the built-in heater that i turned on purposefully. it was my fault for turning the heater on too high and leaving it on for too long.

good advice - i guess i'll wait a few days to see how the yeasties are doing, and if they drop off before i hit FG i'll add in the S04. maybe i'll make a starter first to boost the cell count before re-pitching.