Saving a Yeast Starter?

[Borneogoat]

On Saturday I made a 1.5L starter at 1.037 using DME and WY1450. However, something came up on Sunday and I've had to postpone my brew till next weekend. Sunday night I put the flask with foil cap in the fridge to hopefully save it. About 26hrs on the stir-plate before going in the fridge. I'm thinking the yeast will settle, I can decant most of the liquid, and then pitch when I brew this coming weekend (6-7days in the fridge). Good plan or am I missing something? Concerning keeping the starter sanitary, should I stick with the foil cap or something more air-tight on the flask? And lastly, do I need to warm the starter up before pitching? Maybe pull it out when I start brewing and sit at room temp for a few hours. Or just throw it in the wort straight from the fridge (3-6C)?

 

[Mat B]

I just did exactly that, and have done it a few times in the past. I see no issues with it. I would put a rubber band or something around the foil to stop any contaminants creeping in. The reason for the loose foil is to allow CO2 to escape during it's fermentation, which shouldn't be an issue now that it's finished. I'd also let it come to room temp for a few hours before pitching, as you've already planned, then decant, then pitch.

Don't throw it in cold from the fridge. All advice I've read suggests this can shock the yeast and kill it. I think the aim is to have the yeast and wort at similar temps before pitching to avoid any shock.

 

[Engibeer]

I've done this for a few days but I've always used a bung and airlock.

 

[peteru]

If you have a stir plate, put the starter back on and set to maximum warp. As it comes up to pitching temperature, the yeast will get plenty of oxygen due to agitation, which should help with yeast health during the adaptation phase. If you could be arsed, it's a good idea to add a few ml of your wort to the starter every 5-10 minutes as it warms up.

 

[Rocker1986]

It'll be fine to sit in the fridge like that. I always do this with my starters so I can decant most of the 'beer' off the yeast cake, although I only give them a couple of days in the fridge. A week will be fine though.

Now to throw a cat amongst the pigeons. I've been throwing the cold yeast from the fridge straight into warm wort for months now; after reading a post on here regarding it, I thought I'd give it a shot and see what happened. The result was a way shorter lag time, a healthy fermentation and the beer turned out perfectly fine. Apparently, the yeast build up reserves of trehalose during cold storage, and letting it warm up for a few hours prior to pitching results in the yeast consuming this trehalose as it wakes up, leaving it more vulnerable to osmotic pressure from the wort when pitched. Perhaps this explains the shorter lag times when pitching it cold as opposed to warming it up for hours. It's also my understanding that the thermal shock is a lot worse the other way around, i.e. warm yeast into cold wort.

Is it best practice? I don't know, and I'm not suggesting anything except that it works well for me at least. Try it if you like to see if it works for you or not, or keep to the old warm it up first method, up to you.

 

[ianh]

I do this all the time without any problems. I use wort from my previous brew for my starter (generally brew 1.040 -1.045 type beers). I use a fifth of a smack pack per starter and put 500ml of wort and yeast on stir-plate for 24 hours then add 1000ml of wort and stir for a further 48 hours. I then put the starter in my conditioning fridge at 1C. Decant most of the liquor and allow to come up to room temperature before pitching.

One starter sat in the fridge for 2 months whilst I was on holiday last year then went to work as normal, but it was 1469.

 

[Borneogoat]

So the consensus seems to be: no worries, have a homebrew! I'll sanitize a rubber bung tonight and replace the foil cap. And it seems that warm or cold pitching works.

Thanks everyone!

 

[Lyrebird_Cycles]

Apparently, the yeast build up reserves of trehalose during cold storage, and letting it warm up for a few hours prior to pitching results in the yeast consuming this trehalose as it wakes up, leaving it more vulnerable to osmotic pressure from the wort when pitched. Perhaps this explains the shorter lag times when pitching it cold as opposed to warming it up for hours. It's also my understanding that the thermal shock is a lot worse the other way around, i.e. warm yeast into cold wort.

Yep, we routinely measured alcohol concentrations of over 7% in the supernatant from yeast harvested from beer at 4.7% after a few days of cold storage. Yeast was always pitched cold; it's too hard to warm it up anyway (lousy heat conduction through a yeast cake).

PS if you are worried about the starter, rinse it with concentrated sulphuric acid: get it to pH 2.0 for 15 minutes immediately before pitching.

 

[ianh]

PS if you are worried about the starter, rinse it with concentrated sulphuric acid: get it to pH 2.0 for 15 minutes immediately before pitching.

Would not want to be using concentrated sulphuric acid at home.

 

[Lyrebird_Cycles]

Yeah the usual safety warnings apply.

 

[klangers]

Yep, we routinely measured alcohol concentrations of over 7% in the supernatant from yeast harvested from beer at 4.7% after a few days of cold storage. Yeast was always pitched cold; it's too hard to warm it up anyway (lousy heat conduction through a yeast cake).

PS if you are worried about the starter, rinse it with concentrated sulphuric acid: get it to pH 2.0 for 15 minutes immediately before pitching.

Good info.When you say 'rinse', is the procedure something like a titration of sorts whereby concentrated acid (let's say 50%) is dripped slowly into the starter whilst it is stirring?

 

[Lyrebird_Cycles]

On this scale, yes. What we used to do on an industrial scale was do the titration in the lab, scale up to the volume of yeast and pour the required volume of acid into the yeast tank whilst mixing it over with a lobe pump. You only need a few % of the volume of the yeast: a beaker of sulphuric was enough to do the yeast pitch for a 100 hl batch.

The yeast the acid hits first gets fried (it literally made a smoking hole in the yest mass) but once it mixes in it's OK. IIRC the rationale for using conc. sulphuric was that it was clean, if you diluted it you'd need to sterilise the dilution water. I know that sounds crazy but it's amazing what bugs can live in: we used to get bug counts in 2% caustic held at 60 degrees in the CIP tanks.