My yeast experiments

April 9

For about a year now I have been trying to brew beer. I’ve been moderately successful, but nowhere near what many homebrewers are.

As always I am playing with my food, wondering ‘what if’. This is one of those process blogs which hopefully will get updated on a daily basis over the course of these experiments.

I am trying to answer the question of how can I best propagate and refresh beer yeast.

I am sure it can be done, after all brewers have been brewing beer for millennia and most of that time they did not even know there was this thing called yeast until Louis Pasteur figured it all out.

Here is the problem with yeast and beer. The yeast consumes the sugars, giving alcohol as a byproduct. The trouble is, alcohol kills yeast. So the yeast in one’s trub is, I understand, pretty degraded. For this reason – I believe – the conventional wisdom among brewers is not to reuse your yeast more than 3 times. But, I’m telling myself, that can’t be quite right, as farmers and brewers brewed for centuries without the luxury of a local brew store and yeast makers like White Labs, Wyeyeast and the like. Now on the other hand their beers could all have been like my last batch which fell from 1.065 and stalled out at 1.030. So maybe bad attenuation was the norm.

What I have read is that to propagate and refresh yeast, you should use a weak wort – about 1.030-1.040. This is 1 part dry malt extract (DME) to 10 parts water by weight. I also understand that the optimal amount of yeast slurry is likewise about 1 part slurry to 10 parts wort.

On the bread side of things – we know that bakers and brewers have co-existed and worked with each other for millennia. That is pretty obvious. They both are in the business of propagating yeast and making things from it. In one case, the yeast is nourished by the grain, the other it is nourished by the byproduct of the grain – the barley malt.

So this has led me to trying out a couple of experiments.

Experiment 1: yeast starter from Trub

April 7-8th

In this case I want to find the optimal time and conditions for propagating beer yeast using old trub that has been refrigerated since bottling a few days earlier. My cylinder holds 180ml of liquid and the hydrometer. I’ve combined 17g slurry, 17g DME, and 170g reverse osmosis water, thoroughly mixed and poured into a graduated cylinder with my hydrometer in it at 6AM – 21C. It registered 1.032. During the day there was clear fermentation, but I could not call it vigorous. It probably reached its peak by late evening (15 hours) and by the next morning (6AM) it was down to 1.010. So it would appear that between 15-18 hours is an optimal time – but I need to try it a couple of other times.

The next morning I took 17g of this slurry, 17g of DME 170g of H2O stirred, and repeated. That one is still ongoing. 12 hours on it has slowed up.

Experiment 2: bread starter

April 8

The extra slurry got me thinking about bread starter. What if I used that slurry to propagate a bread starter the same way I would my usual starter. The difference would be that it would not have the time to begin developing lactic acid bacteria. But might it be more effective at restoring yeast strength than my wort?? So: 100g of that 1st night slurry and 60g whole wheat flour. It really took off and was bubbling away within an hour. (Lag time? What’s that? ) I decided to let it go for a couple of hours. Then my next step: to use this as a slurry instead of the trub from the beer. This was set up at noon, its now 5PM and it appears to be going strong, though the hydrometer is still reading 1.030. I’ll monitor it through the evening. This setup had 17g of the 166% starter, 17g DME, 170g H20

Experiment 3

Onto the bread: (April 8)

I still had about 50g of the first nights slurry left over after experiment 2. . What to do with it? What about bread? So: I mixed up a white baguette dough – 80% hydration, (300g AP flour, 50g slurry and 190g water, 6 g salt. It too has been fermenting nicely. After 6 hours I poured it (well – it was the best it would handle!) in a baguette liner and stuck it in the fridge. I can tell it’s going to be quite chewy. (PS: It was indeed chewy. It had a fairly tight crumb, and was not quite as flavorful as sourdough. )

This experiment goes to show that with a little yeast of any kind you can do things with. You just need to make sure your flour is weighed, the salt comes in at 2% and you are specific in your hydration. I tend to go with multiples of 100g as this becomes easy to sort out the salt and liquid. A 300g flour at 70% hydration therefore needs 6g of salt and 210ml (g) of water. Using a slurry like this means that it needs to be calculated as part of the water.

Experiment 4: Yeast starter from the bread starter

April 8

Since the bread starter (experiment 2) was so resoundingly fast acting, I wondered about turning it back and using it to propogate a beer starter.

April 8, noon

So following my now usual ratios, I took 17g of this very active starter, mixed it with 17g DME and 170g H2O. I used my hydrometer cylinder and hydrometer to check on its progress. It started at 1.030.

April 8: 8PM

WTF!!! The hydrometer reading is at 1.040. What happened?

April 9 9:00AM

Its still active, reading at 1.020. I’ve also refreshed my sourdough starter, and thinking of using some of this starter to do sourbeer as it will have the lactic acid bacteria going strong. I’m thinking of doing a second gallon of beer using the flour starter from Experiment 4.

Time to make some beer….

2 PM April 9

I refreshed my 2 little experiments – the one using only the trub, and the one that had had the flour as food as well. In both these cases, I used 200g H2O, 20g starter and 20g DME. Both have started at 1.030. My plan is to brew 2 gallons, but pitch one gallon with one yeast and 1 gallon with the other.

April 10th

Brew day! Somehow I messed things up but it should turn out ok in the end. I added too much water. I needed to add a bunch of malt extract to bring things to an acceptable og (1.062 when all is said and done). But it worked out as I have enough wort for 3 x 3 litre jugs. The third will be pitched with safale 04 as a kind of control sample.  I pitched all 200g of the refreshed starter from the 2 experiments, and 20% of the Safale04 yeast which is normally intended for a 5 gallon brew (yes I hydrated it for about 30 minutes in 50ml of RO water). I also added 4g of yeast nutrient to each batch. All is good.

April 11

20 hours after pitching, all 3 jugs are actively fermenting. The two which used the old trub refreshed a couple of times are significantly more active than the Safale04 control sample. This is very hopeful because I would dearly love to be able to keep developing my own yeast for beer in the way I do for bread.

April 23 Fermentation is done!

My experiment 2 jug comes in at 1.012 YAAAY!  (6.65%)

This is the one where I added flour to the starter and let that develop

My experiment 1 jug came in at 1.018. Respectable. Better than stalling out in the mid 20’s. (5.85%)

My ‘control’ jug with safale04 yeast comes in at 1.020. (5.58%)

I have not yet bottled them  – that will come likely tomorrow.

Generally they all taste the same – a decent ale – nothing to be ashamed about.

Some tentative conclusions:

It would appear that the addition of flour to the trub and allowing it to ferment in the same way one would do with sourdough has strengthened the yeast. It is worth pursuing this more.

It would also seem that refreshing the yeast with successive fresh wort, leaving it a day between each one also makes for a stronger yeast than the basic dry yeast.

Further explorations and questions:

  1. I need to explore 2 ways of working with the flour: The variable is the point at which the flour is introduced.
    • refresh trub with wort once, refresh that with flour, refresh a third time with wort
    • begin the trub refresh with flour and then a second and third time with wort.
  2. I still want to work more with refreshing the trub with wort. I have 2 main questions here:
    • What is the optimum number of times to refresh before I hit the law of diminishing returns?
    • How much should I pitch? Which gets at one of the biggest questions: What’s really my cell count?