Using a magnetic stirrer for yeast starters

[Cheap Charlie]

22 hours ago, Shamus O'Sean said:

MAKING A YEAST STARTER INCLUDING AN OVERBUILD FOR THE NEXT BREW.

PDF version for easy printing: 

Making a yeast starter including an overbuild for the next brew.pdf 2.84 MB · 4 downloads

Introduction

Classic Phil just got a stir plate for doing yeast starters.  So I thought I would do a bit of a repeat of a thread from a few years ago when Otto demonstrated his yeast starter method.  The process includes doing an overbuild.  That is where you make enough yeast cells for the beer you are going to brew plus extra yeast to harvest and save for making another starter for the next brew.

Most of the equipment you will need to make a yeast starter.  Dry Malt Extract, a 3 – 5 litre borosilicate glass flask, magnetic stir bar (small white thing in front of the flask), funnel, scales, spray sanitiser, spoon, pot, stir plate, aluminium foil.  You do not need a stir plate; instead you can give the flask a shake every time you walk past it for the first 24 hours.

 

Yeast calculators

The first thing is to figure out how much yeast you need for your brew and how many active yeast cells you are starting with.  Do not be put off by the big sounding numbers.  Use a yeast starter calculator to figure out the numbers including the overbuild.  Brewers Friend or BrewFather are two examples of software you can use. 

The calculators use the wort gravity, volume, target pitch rate, yeast type, number of packets or grams to figure out how much yeast is needed for your brew.

If doing a starter with dry yeast, I assume 18 billion cells per gram of yeast.  This assumption is fine as long as the yeast is still in date and has been stored in the fridge.  I usually rehydrate the dry yeast in 10 times its weight of 30°C boiled and cooled water.  This step gives the yeast the best chance for maximising the number of healthiest cells.  However, you can pitch it straight in from the packet.

Liquid yeast usually states how many yeast cells are in the packet when it is packaged.  Yeast deteriorates over time.  The yeast calculators use the manufacturing date to tell you how many cells are left after a certain time.

Yeast slurry from a previous ferment has about 1.5 billion cells per ml of slurry.  It dies off too, so call brewday plus 3 days the date of manufacturing and allow for loss of viability.

If you are using an overbuild from a previous starter, you would have begun with a known cell count and will know how many cells were in your overbuild when it was harvested.  Add 2 days to the date you did the starter and call that the date of manufacturing and allow for loss of viability.

In my case I use BrewFather.  In the example below, I had made an overbuild of 200 billion cells of US‑05 on 6 November.  I was doing the next starter (for my Kaiju Krush) on 25 December.  In the 46 days since making it, the overbuild had dropped to 68% viability, so it only had 135 billion viable cells left.  The brew I was doing this starter for was 30 litres of 1.045 OG wort.  The calculator said I need 266 billion cells of US‑05.  Plus I wanted to make another 200 cell overbuild (not sure why the screenshot below says 199 billion cells overbuild).  So to make the total 466 billion cells, I needed to make a 2.4 litre starter with 236 grams of Dry Malt Extract.  Once the starter has finished fermenting, I have to harvest 1.03 litres to save and leave 1.37 litres in the flask for the Kaiju Krush.

The first day - Starting the starter (about 45 mins prep time and 45 minutes cooling time)

Now you can weigh out the DME and add the water, pour it into the flask and boil the starter wort in the flask.  I do that if the starter is less than half of the volume of the flask.  As others have pointed out, the issue is possible boil-over in the flask.  Some DME is more prone to boil-over than others.  To play it safe, as the starter in this case is close to half the capacity of my 5 litre flask, I am going to boil the starter wort in a pot then add it to the flask.

The flask still needs to be sanitised/sterilised.  Therefore, firstly drop your stir bar in the flask, pour about 1 litre of hot water into the flask and pop the funnel in the flask for a boil to sterilise.  We will use the funnel later.

You might note that I do not use anything to diffuse the heat from the gas burner.  Maybe not best practice, but all of my flasks (2 x 3 litre + 1 x 5 litre) have not had an issue.

 

Next weigh out the DME.  Then pour in the volume of hot water.  Use the scales to measure the correct amount of water.

   

 

It does not matter if your measuring is not 100% accurate.  Stir in any DME that has not dissolved.

   

 

Pop the starter wort on the stove to boil.

 

Now is a good time to get out your previous overbuild that was stored in the fridge.

 

I use alcohol swabs to sterilise the rim of the jar.  So go ahead and swab the rim.  Then let it dry for a minute or two.

   

 

Decant off most of the beer above the yeast.  Leaving mostly yeast in the bottom of the jar.  I suggest covering the jar with its lid or a piece of aluminium foil, sprayed with sanitiser.

   

 

By now, your flask of water should be boiling.  You will see that I have also inverted the funnel over the mouth of the flask to steam sterilise the inside of the flask.  You want to expose the funnel inside and outside to a few minutes of steam.  Once the funnel is sterilised, set it aside.  Grab the square of aluminium foil and wrap it around the mouth of the funnel using oven gloves.

   

 

The foil only has to be loosely wrapped around the mouth of the flask.  Set a timer for 3 minutes.  The escaping steam will sterilise the inside of the foil.

   

 

By now the starter wort will be boiling.  Set a timer for 5 minutes.  Give the boiling wort an occasional stir.

   

 

Once the 3 minute timer is up, remove the flask from the heat using baking gloves because the flask will be boiling hot.  Carefully remove the foil “lid” and set it aside.  Empty out the boiling water, being careful to not let the stir bar side out of the flask.

   

 

By now, the 5 minute timer for the starter wort boil should be finished.  Stand the flask.  Fit the funnel.  Remove the starter wort from the heat and carefully pour into the flask.  Remove the funnel and refit the foil “lid”.

   

 

Using gloves, pop the flask into a warm water bath.  These flasks are meant to be able to withstand boiling to freezing temperature changes, but I do not take the risk.  Rather than a small sink for your “bath” you can use any pot or vessel that will withstand the heat of the flask.

 

I leave the flask in the warm water for about 8 minutes.  Give the flask a swirl every now and again to help with the heat transfer.

 

Then I dump the now hot water and fill up the “bath” with cold water.  Leave it for another 8 minutes or so.  Repeat this process 4 -5 times or until the starter wort is 20 – 25°C.

 

Give the yeast in the jar a good swirl around to make it creamy.  Use another alcohol swab to sterilise the rim of the flask.

   

 

And the yeast jar.  And clean and sanitise the funnel from before.

   

 

Decant some of the starter wort from the flask into the yeast jar.  Wipe up any drops with the alcohol swab.  This will help to stir up the yeast and make it pour easier.

   

 

Once nice and runny, use the funnel to pour the yeast into the flask.  Wipe up any drips with an alcohol swab.

   

 

To make sure I get as much of the yeast out of the jar as possible, I pour some more of the starter wort back into the jar a second time.  Give it a swirl and pour back into the flask.

 

Now put the foil “lid” back on the flask.  Slightly tilt the flask so the magnetic stir bar is at the underside outer edge of the flask.  Slide the flask onto the stir plate so the position where the stir bar was passes across the middle of the stir plate.  The magnets under the stir plate should attract the stir bar and move it to the centre of the flask as you continue to slide the flask across the stir plate.  Make sure that flask is sitting centrally on the stir plate.

Turn on the stir plate and adjust the speed so that a vortex is created in the middle of the wort.  But not so fast that the stir bar spins off to the side of the flask

 

The photo above was just so you can see the vortex a bit better.  I actually put the stir plate and flask into a cardboard box in the lounge room where the temperature stays pretty constant.

 

Temperature of the starter is not so critical because you are not worried so much about off flavours. You are just growing more yeast.  Having said that, in the middle of winter, I will put a heat belt in the box (hence the porcelain tiles in the box).  Set it on 18°C so the wort does not cool down too much.  I never worry about keeping the starter cool.  However, the lounge never gets above 25°C anyway.

Leave the starter on the stir plate for 12 hours.  Some leave it longer, like 24 hours.  However, I read/heard somewhere that much more than 13-14 hours does something to the yeasties like stretching their molecules and affecting their fermenting performance.

The fourth day – Harvesting and storing the overbuild and retaining the yeast for brew day (about 45 mins prep time)

After 12 hours turn off the stir plate and leave the yeast to ferment out over the next 36 – 48 hours.  By that time it will look something like this.  You can see how the Krausen rose up the flask.  Do this in a 3 litre flask and you would have a Krausen volcano.

 

You can also see the layer of new yeast at the bottom.

 

Give the flask a swirl to knock most of the Krausen back into the liquid.  I also use another stir bar on the outside of the glass, to lift the stir bar inside the flask and swirl it around on the inside wall of the flask to clean the Krausen back into the liquid.

 

Once all the Krausen is cleaned off, get the stir bar back into the middle of the flask and turn the stir plate back on.  I leave it for 30 minutes or so.  By that time the yeast has completely mixed evenly into the liquid.

 

While the yeast is being mixed up, sterilise a jar, lid and tongs for storing the overbuild volume.  I usually use enough water to 3/4 fill the jar on its side.  Once at a boil, I leave it for 3 - 5 minutes.  Then I use the tongs to turn the jar over and boil it for another 3 – 5 minutes.  The overbuild from this starter will be stored in this Mason jar.

 

Remove the jar and the lid with the tongs and store to cool down.  By the time the yeast is mixed up, the jar should have cooled to room temperature.  You want it less than 30°C.  If it is still a bit warm, I will sometimes run the outside of the glass under a cold tap, being careful to not get any water inside the jar.  Do not do this with a jar freshly out of the boiling water.  Cheap Mason jar glass is too fragile and will break if switched from hot to cold too quickly.

 

Once the yeast is well mixed, turn off the stir plate and remove the flask.  Take off the foil “lid”.  Use another alcohol swab to sterilise the mouth of the flask.

 

Use another stir bar, held on the outside of the flask, to carefully remove the stir bar from the flask by attracting it from the bottom of the flask and dragging it up the inside of the flask.  Using a finger, without touching the inside of the flask, I press on the stir bar and slide it out of the flask.

 

Swirl up the yeast in the flask again because, even in this short space of time, it will have started to settle on the bottom again.  You want it as evenly spread through the liquid as possible. Decant the desired volume of overbuild from the flask into the Mason jar.  I use kitchen scales, zeroed after the Mason jar is placed on them.  Assume 1 gram of liquid is 1 ml of liquid.

 

Gently turn the lid onto the Mason jar.  Do not tighten it up.  Leave it loose enough to allow any build-up of air to escape.  The concoction should not ferment anymore because it should be fermented out already.  Plus you are putting it in the fridge that will inhibit further fermentation too.  Put the Mason jar in the fridge.  This is the overbuild that will be used for our next starter.  I realised after putting this in the fridge that it was a US-05 yeast, but I had wrongly used a CCA (Coopers Commercial Ale) label.  Within a couple of days, the yeast will have settled to the bottom like the Czech Lager yeast in the Mason jar beside my US-05 yeast.

 

Put the foil “lid” back on the flask and put it in another fridge to allow the yeast to settle out to use in the upcoming brew.

 

 

 

Wow, this is excellent. Thanks @Shamus O'Sean. I have printed this out and put into my brew bible (which is located in the pool room)

[Shamus O'Sean]

41 minutes ago, Cheap Charlie said:

Wow, this is excellent. Thanks @Shamus O'Sean. I have printed this out and put into my brew bible (which is located in the pool room)

You do not have to have all the gear to do it either.  Replace the flask with a sanitised cordial bottle.  Obviously don't boil it though.  Give it a shake every half hour, much like doing a Coopers Commercial Yeast reactivation.

Nice to know you keep your brew bible in the most important room in the house.

[Cheap Charlie]

4 minutes ago, Shamus O'Sean said:

You do not have to have all the gear to do it either.  Replace the flask with a sanitised cordial bottle.  Obviously don't boil it though.  Give it a shake every half hour, much like doing a Coopers Commercial Yeast reactivation.

Nice to know you keep your brew bible in the most important room in the house.

I don't have a stirrer yet, but I don't like the look of the wort whipper, I will probably get the older model. I started using an old soda water bottle, but now I have upgraded to Moccona coffee jars.

[Shamus O'Sean]

13 hours ago, Classic Brewing Co said:

Cheers Shamus, I am sure your tutorial will help others too, so you have done well, I for one will save it & the PDF & try to get it sorted.

All I was doing before as gathering a quantity from the bottom of the FV, whack it in an Erlenmeyer Flask covered, whack it in the fridge up to about 2 weeks.

I got away with it a few times, but I was never sure about the quantity, last time I used about 600ml which appeared to be too much.

I realise now that it is a very different process.

Cheers.

Harvesting the trub is quite different.  You can collect enough yeast that you do not need to do a starter.  It does deteriorate like any liquid yeast, but you either re-use it quickly or harvest enough that any die-off does not matter.

Remember slurry has about 1.5 billion cells per ml of slurry, but that measurement is of the settled slurry once cold crashed in a jar in the fridge.  So if the average 23L of 1.043 OG wort needs about 200 billion cells you only need about 150ml of fresh settled slurry.

[Shamus O'Sean]

3 minutes ago, Cheap Charlie said:

I don't have a stirrer yet, but I don't like the look of the wort whipper, I will probably get the older model. I started using an old soda water bottle, but now I have upgraded to Moccona coffee jars.

That will do it.  Wider mouth is easier to deal with.  Being glass you can slowly bring it to the boil to sterilise if you want.  Not sure about the lids though.  Are they "hollow" glass?  Maybe do not boil them.

[Cheap Charlie]

1 minute ago, Shamus O'Sean said:

Harvesting the trub is quite different.  You can collect enough yeast that you do not need to do a starter.  It does deteriorate like any liquid yeast, but you either re-use it quickly or harvest enough that any die-off does not matter.

Remember slurry has about 1.5 billion cells per ml of slurry, but that measurement is of the settled slurry once cold crashed in a jar in the fridge.  So if the average 23L of 1.043 OG wort needs about 200 billion cells you only need about 150ml of fresh settled slurry.

Yeah, I usually fill a coffee cup with the trub and chuck that in (≈250ml). It seems to be an over pitch, ferment is done in a few days, sometimes 48 hours, but the beers certainly do turn out a lot cleaner. 

[Cheap Charlie]

2 minutes ago, Shamus O'Sean said:

That will do it.  Wider mouth is easier to deal with.  Being glass you can slowly bring it to the boil to sterilise if you want.  Not sure about the lids though.  Are they "hollow" glass?  Maybe do not boil them.

I have already cracked one by heating it and cooling it . I don't really bother with the lid because it is plastic, maybe spray it with some sanitiser. For the glass jar I use boiling water and let it cool.

[iBooz2]

Just to update everyone on what I use to sanitise the lips/rims of glass vessels.  Just a clean piece of paper towel soaked in Isopropyl Alcohol rather than those disposable wipes as they are expensive.  You can by a 500 ml spray bottle from Bunnings and it will last you ages so long as you clip the vapor cap back on after each use.

Back when I was working I had cartons of those Iso wipes but I cannot justify the expense now as no longer tax deductible.

[kmar92]

On 1/5/2023 at 10:13 PM, Shamus O'Sean said:

Temperature of the starter is not so critical because you are not worried so much about off flavours. You are just growing more yeast.  Having said that, in the middle of winter, I will put a heat belt in the box (hence the porcelain tiles in the box).  Set it on 18°C so the wort does not cool down too much.  I never worry about keeping the starter cool.  However, the lounge never gets above 25°C anyway.

Leave the starter on the stir plate for 12 hours.  Some leave it longer, like 24 hours.  However, I read/heard somewhere that much more than 13-14 hours does something to the yeasties like stretching their molecules and affecting their fermenting performance.

I have been re-reading your great post regarding yeast starters @Shamus O'Sean.

If I may, a couple of points. Palmer reckons that the temperature of the starter should be in the vicinity and your intended fermentation temperature as this way you are breeding yeast cells that are acclimatized for the actual brew. I am not saying that the temperature is critical but I guess anything that can be done to help the yeast is a bonus. Secondly, Palmer also states that the initial time the starter is on the stir plate with a vortex going is conducive to incorporating oxygen into the wort to help the yeast during the yeast adaption phase (lag phase). After the yeast have reached the next stage - attenuation or high growth phase, then oxygen is not good to have in the wort so it is better to then have the starter removed from the stir plate or switch it off.

[Shamus O'Sean]

2 hours ago, kmar92 said:

I have been re-reading your great post regarding yeast starters @Shamus O'Sean.

If I may, a couple of points. Palmer reckons that the temperature of the starter should be in the vicinity and your intended fermentation temperature as this way you are breeding yeast cells that are acclimatized for the actual brew. I am not saying that the temperature is critical but I guess anything that can be done to help the yeast is a bonus. Secondly, Palmer also states that the initial time the starter is on the stir plate with a vortex going is conducive to incorporating oxygen into the wort to help the yeast during the yeast adaption phase (lag phase). After the yeast have reached the next stage - attenuation or high growth phase, then oxygen is not good to have in the wort so it is better to then have the starter removed from the stir plate or switch it off.

Hence the reason to turn off the stir plate after about 12-14 hours.  But it does make sense to try to grow , say a lager yeast at 12°C.  However, achieving that is more challenging.  I do not have a temperature controlled yeast growing fermentation chamber. 

[kmar92]

I have an improvised one! I guess that if I got the timing correct I could do a lager yeast starter in conjunction with a lager fermentation.

[iBooz2]

It's usually late in the afternoon or early evening when I pitch into a starter, that is just the way my daily routine works out.  I am very fussy with temp control but not spinning time control, so the stir-plate does not get switched off until sometime the next morning, which maybe up to 18 hours later after pitch.  I use a wine cooler fridge and an STC for my starter temp control cabinet.

Edited February 26, 2023 by iBooz2

[kmar92]

21 minutes ago, iBooz2 said:

It's usually late in the afternoon or early evening when I pitch into a starter, that is just the way my daily routine works out.  I am very fussy with temp control but not spinning time control, so the stir-plate does not get switched off until sometime the next morning, which maybe up to 18 hours later after pitch.  I use a wine cooler fridge and an STC for my starter temp control cabinet.

I wouldn't think that 18 hours would be a problem, oxygenation wise. After all you are just trying to make healthy yeast cells, not beer. To my way of thinking, and apparently to Palmer's way of thinking also, temperature would be far more important, i.e. building yeast cells that are adapted to your intended fermenting temperature so once they get into the wort they are best adapted to the environment and healthy.

Edited February 26, 2023 by kmar92

[Otto Von Blotto]

Does temperature make much of a difference if it's gonna be chilled down for a day or two prior to pitching it though? It may be more of a thing when pitching them active.

I've never worried about the temperature of starters other than making sure they're warm enough in winter when I'm doing ales. Haven't noticed any problems in the beers and I can't see how maintaining the starter around the brew's fermentation temp would make any noticeable improvement to them.

After all, the idea is to grow yeast, and they prefer to operate in temperatures higher than we ferment our beers at.

[kmar92]

11 hours ago, Otto Von Blotto said:

Does temperature make much of a difference if it's gonna be chilled down for a day or two prior to pitching it though? It may be more of a thing when pitching them active.

I've never worried about the temperature of starters other than making sure they're warm enough in winter when I'm doing ales. Haven't noticed any problems in the beers and I can't see how maintaining the starter around the brew's fermentation temp would make any noticeable improvement to them.

After all, the idea is to grow yeast, and they prefer to operate in temperatures higher than we ferment our beers at.

I am not a microbiologist, so I really cant answer your question. Maybe temp makes little difference, but my reading of Palmer he implies that having the starter near fermentation temps helps to have yeast cells acclimated to the ferment temp which would assist the yeast in the 1st stage of fermentation. Whether chilling the yeast starter before using for a ferment makes that scenario different - I don't know. Chilling will just make the yeast go dormant so maybe when they are woken up in the ferment they are still acclimated to the fermenting temperature, or maybe they are not and have to adapt again?

[Otto Von Blotto]

1 hour ago, kmar92 said:

I am not a microbiologist, so I really cant answer your question. Maybe temp makes little difference, but my reading of Palmer he implies that having the starter near fermentation temps helps to have yeast cells acclimated to the ferment temp which would assist the yeast in the 1st stage of fermentation. Whether chilling the yeast starter before using for a ferment makes that scenario different - I don't know. Chilling will just make the yeast go dormant so maybe when they are woken up in the ferment they are still acclimated to the fermenting temperature, or maybe they are not and have to adapt again?

Neither am I and theoretically it makes sense, I'm just not sure how much difference it makes in practice - unless you pitch 30 degree yeast into 15 degree wort which isn't advisable from what I have read. 

I've never done the active starter pitching though, which is a scenario where I'd think keeping the temperature similar would have more benefits. I've always chilled them and tipped out most of the spent wort, and for a number of years now I've pitched the yeast still cold. They always get going pretty quickly and produce beers that taste great and as expected; trying to control the starter temp just seems like unnecessary hassle for me

[Tricky Micky]

Great thread here by the way. I thought I'd post this for all of us who haven't yet started collecting CCA yeast from Coopers commercial offerings. Nice and simple to follow.

 

Edited March 1, 2023 by Mickep

[stquinto]

That's great info, thanks to all who contributed, especially @Shamus O'Sean for the PDF. Like @Cheap Charlie I'll print it out for my Bible

I was thinking of getting one of these setups. I'll have to get a smalle camping gas stove though as I have an induction cooker. I also have a few packs of out-of-date Wyeast strains (the oldest was to be used before July 22). If I made up a starter and used the stirring plate, do you reckon they could still be viable ? Likewise I have some old-ish dried packs (maybe best by Nov 22). Shame to chuck them but even worse to waste the time spent on a brew onyl to ruin it with iffy yeast.

Cheers

[Shamus O'Sean]

6 hours ago, stquinto said:

That's great info, thanks to all who contributed, especially @Shamus O'Sean for the PDF. Like @Cheap Charlie I'll print it out for my Bible

I was thinking of getting one of these setups. I'll have to get a smalle camping gas stove though as I have an induction cooker. I also have a few packs of out-of-date Wyeast strains (the oldest was to be used before July 22). If I made up a starter and used the stirring plate, do you reckon they could still be viable ? Likewise I have some old-ish dried packs (maybe best by Nov 22). Shame to chuck them but even worse to waste the time spent on a brew onyl to ruin it with iffy yeast.

Cheers

The Wyeast packs are worth trying to reinvigorate. The trickiest part is figuring out or making an educated guess on the viability.  Yeast calculators can do that for you.  The same calculators will usually help you figure out the size and how many step-ups are needed to get enough healthy yeast.

I have a jar of 150 billion cells of White Labs American Lager WLP840 from Oct 2021 that is probably cactus, but I cannot bring myself to chuck it.  If it costs more in dry malt and a bit of power to bring it back to life, I should just buy fresh yeast when I need it.

With dry yeast, that was use-by 4 months ago, I would just make a starter assuming 50% viability or about 100 billion healthy cells.  Otherwise, just chuck 2 packets into your brew.  It also makes great yeast nutrient.  Just chuck it into the boil with 5-10 minutes to go.

[Cheap Charlie]

1 hour ago, Shamus O'Sean said:

If it costs more in dry malt and a bit of power to bring it back to life, I should just buy fresh yeast when I need it.

I have a 5 month old jar of CCA in the fridge, not sure whether to keep it on life support or just pull the plug. I suppose I could see how it goes with sugar, but you're right not really worth wasting time and dry malt to raise the dead horse.

[Otto Von Blotto]

They survive longer than you think, the online calculators are pretty conservative when it comes to viability. A few years ago I did my own viability testing and found a considerable difference between my observations and the calculators the longer I kept it, in short the viability didn't drop as quickly as they would suggest. 

I resurrected the three strains I keep in the fridge after probably more than 6 months in order to ferment the recent batches. I just made a small starter for them about a litre in size to check if they were ok, and they all were. 

2021 might be pushing it a bit though

Edited March 2, 2023 by Otto Von Blotto

[Greenyinthewestofsydney]

In my experience it depends what the yeast has been sitting under. If it's a sample from an unhopped starter sitting under 2 or 3% ABV beer then I have resurrected them 18 months after putting them in the fridge. If it's a slurry and sitting under say 5% ABV beer then by the 6 month mark you would have almost nothing alive in there. You can see by the colour. Light grey means a lot of death. Darkish grey is basically total death.

[Otto Von Blotto]

Fair point. I will point out that those viability tests were done with yeast sitting under unhopped starter "beer" as is my normal practice with harvest and reuse. 

[Shamus O'Sean]

13 hours ago, Cheap Charlie said:

I have a 5 month old jar of CCA in the fridge, not sure whether to keep it on life support or just pull the plug. I suppose I could see how it goes with sugar, but you're right not really worth wasting time and dry malt to raise the dead horse.

If you had 400-500 ml of yeast cake in the jar and clear beer above it, I think you could resurrect it.  A 2L starter with 200g of LDM would be enough.  The CCA is pretty robust.

[Cheap Charlie]

12 hours ago, Shamus O'Sean said:

If you had 400-500 ml of yeast cake in the jar and clear beer above it, I think you could resurrect it.  A 2L starter with 200g of LDM would be enough.  The CCA is pretty robust.

I will give that a go. I just got some novalager yeast so keen to try that and put the CCA on the bench for a while.