Re-using the yeast cake?

[Toxxyc]

OK I've got a question. A few weeks ago I made a rum wash, 20 litres. I used 1kg molasses and 2kg brown sugar into 20l of solution, so not very strong. Into that I pitched 15g of S-04 beer yeast (had some on hand) as well as a packet (20g) of bread yeast.

I wrapped the whole thing in my half electric blanket, set it to hot (around 32°C) and left it there. In a week it was done fermenting. I let it sit for another week and then poured the wash off into a sanitized cube, sealed it and set it aside for stripping later.

Not wanting to waste the yeast colony in the fermenting container, I pre-mixed a few kilos of brown sugar in water and after cooling, poured that into the container straight onto the yeast cake. I've done this with beer many times and it usually results in a faster, stronger fermentation as there's a crapload of yeast in the cake, as well as a lot of dead yeast that works as nutrients for the live yeast. Sounds good?

Nope. I set this whole thing in the electric blanket again and set the temp up to 32°C again. The first few days went well and I saw a lot of CO2 escape from the osmosis cap. It slowed down and stopped completely after about 6 days so I removed the blanket and set it aside to let the yeast drop out a bit, thinking I'll run the sugar and the molasses washes together in the kettle in a single strip.

Stripping day came and I opened the molasses wash, gave it a quick taste to confirm there's no sugars left and it was dry and tart, exactly like it should be. All good.

Opened the sugar wash, gave it a taste and it was sickly sweet. Obviously, fermentation wasn't complete. I figured it must then be a pH thing and as I know a sugar wash can get relatively acidic, I poured in a tablespoon of sodium bicarbonate I had on hand. Off topic, but in hindsight I should have known this was a BAD idea. I got a HUGE reaction and the wash came spewing out of the container like mad. LOL.

Cleanup done and all that and now fermentation is going again. I wrapped it in the blanket again, and it's fermenting, but SUPER slow. I'm guessing (after some Googling) that the Bicarb simply didn't have enough power to raise the pH enough in order to let the fermentation complete.

So now, because I don't want to spend the next 6 weeks waiting for this thing to finish, how can I speed this process up? I don't think we get oyster shells here, as it's South Africa and this place is a bit of shithole when it comes to lots of things. Can I use a swimming pool alkalinity booster like soda ash (Na2CO2)? Or is there a better way to boost this thing to completion?

PS: I just want it to finish as I got better yeasts to use and I need the vessel it's fermenting in. Otherwise I would have just left it to do it's thing.

[still_stirrin]

... Can I use a swimming pool alkalinity booster like soda ash (Na2CO2)? Or is there a better way to boost this thing to completion?

So, as you’ve noticed, trub (dregs or “yeast cake”, as you’ve called it) can be acidic, and depending from what was the ferment may tend to be quite acidic, to the extent that a new wash won’t even kick off without pH correction.

A good base (pH booster) is calcium hydroxide (pickling lime), often found in the grocery store in the canning supplies section. It is a much stronger base than bicarb soda and even better than soda ash. Plus, the calcium is a good nutrient for the yeast. Hydrate a tablespoon of it in warm water and then gently pour it into your fermenter, swirling (not stirring vigorously) it into the wash. Activity will start after a short time and hopefully it won’t be explosive like your baking soda addition.

Check the pH after this addition. You may need to repeat it a time or two to get the pH back up to 4.5, or so.

Give it a try.
ss

[Setsumi]

on oyster shells, any shel from the beach will work, the old beat up limpets prolly the best for pickup. any feed store should have shells for chickens ask for skulpgruis.

you can use egg shells also. myself use chalk or bordkryt. just buy the better known brands and whatch out for the china imports.

it is better to start the addition before fermentation.

think SS has the better option in your case.

[Demy]

Sugar washes are easy to prepare but you need to pay attention to nutrients and pH. A good nutrient I often use is the boiled yeast for a few minutes, sometimes I add a bit of flour to the mix and works well. The pH must be adjusted immediately (use what you find as mentioned by others) and then kept in the correct range using something that is buffer (oysters, eggs, marble flakes etc)) because sugar washes tend to lower the pH while Fermentation proceeds. If you do this you can safely reuse your yeast.

[Saltbush Bill]

. I got a HUGE reaction and the wash came spewing out of the container like mad. LOL.

Most of us have learned that lesson the hard way....no stopping once the eruption starts.

[NZChris]

You need to know what you pH is, not guess. Strips are a little bit tricky for colorful washes like rum, but if that's all you've got, use them.

If the pH is too low, shells are pretty useless unless you first heat them to glowing red hot for long enough to convert them into Quicklime, then make Calcium Hydroxide.

[Toxxyc]

Thanks guys. Yeah I'm a beer and mead brewer so I'm familiar with the use of nutrients. As nutrients I used an old yeast cake from a lower ABV beer I made and dumped the boiling hot molasses wash straight onto it, and sealed the can. That killed everything in the old yeast cake, and after cooling I added the yeast to the fed container with wash.

I just really didn't expect the pH to tank THAT fast. I'll have to get something to buffer it with then. Happy to spill a bit if it means I don't lose the wash. I'll take a look when I'm at the shops in a bit. In the meantime I'll be making a new wash with a bit more molasses and whatnot, using the correct procedures from the start. Also think I should get a pH meter sometime. I'll help both my distilling and my beer making, I'm sure.

[Tummydoc]

You can use swimming pool pH increaser, you'll get a more violent eruption than baking soda. Probably a geiser if you ferment in a carboy but not a problem in a garbage can or bucket. You need a pH meter to adjust, target a pH of 4-4.5 to restart a stuck ferment.

[Teddysad]

Best practice is to use potassium bicarbonate, pre dissolved in water. and added gradually to achieve the desired pH. Then use Calcium carbonate in form of sea or egg shells, or natural chalk to maintain that pH. You can take it a step further and make a full buffer with citric acid to stop rising pH but in our realms , rising pH is not normally a problem