Underpitching Yeast

[Keifer]

So i read in a wheat thread some ways of making it more bananary. One of the ways would be to underpitch the yeast, resulting in more banana flavour. What about ale yeasts, if you under pitch these how does it affect the taste? and by how much?

Reason i ask is i made a batch the other day and used a starter of a brit ale 2 yeast that i done probably 3-4 months previous. It took best part of 3 days to show signs of activity. This would sort of equate to underpitching and am wondering out of sheer curiosity if it would have change the flavour at all. Not worried about the beer at all, just how the little critters go about their work

Cheers,
Keith

 

[Trent]

I am pretty sure that underpitching to the point where you have a 3 day lag time can allow some bugs and stuff to get a hold to start with, and maybe leave their little pawprints in the flavour of the beer, and also put the beer yeast under some sort of stress. I think that it will increase the esters, which isnt so bad in a british beer, but may make them more dominant than you want. IIRC, yeast also put out fusel alcohols (the hot ones) when they are reproducing and growing, so may make the alcohol have a hot sensation. I assume the wheat yeasts that perform better when underpitched and slightly stressed have evolved to work in these sorts of conditions, but I think that there is a difference between underpitching to slightly stress, and really underpitching, which may cause the yeast to cark it early, or put out some unwanted byproducts. I am sure that the beer will be fine, but I would say for me that a 3 day lag time is probably a little more than I would be comfortable with, and the beer may not be as good as it could be. Be interesting if you could report back any observations about how the beer fares, cause I am wrong more often that I would like to be
All the best
Trent

 

[pint of lager]

Pitching a 3-4 months old starter is a bad idea. There are minimal yeasts alive. Once yeast flocculates, they start dying off at a great rate. After 3-4 months, you would be lucky to have 1% of them alive.

Infections and wild yeasts multiply at 10 times the rate of yeasts. They can quickly build up numbers and overwhelm your yeast.

One of the golden rules of brewing is to pitch a large quantity of healthy hungry yeast. They quickly change conditions in the wort making it unfavourable for wild yeasts and infections to take hold. Yeast consume the available oxygen, lower the pH and start producing alcohol, all of which make it hard for infections to continue to thrive.

Next time you have an old starter, pour off the waste beer and add 100 ml of sanitised 1.040 wort. Try to keep everything as clean and close to sterile as you can.

When this shows signs of active fermentation, step up to 1 litre, then when that is going, pitch to your brew. Always step up your actively fermenting mini starter in steps of 10, for example 100 ml to 1,000 ml.

The standard rate of starter is 5% for ales and 10% for lagers. So for an ale brew of 23 litres, you want an active starter of at least 1.5 litres. If you want to try underpitching, then use half of the suggested standard rate of starter.

3 days lag could mean that your brew is seriously infected. It would take a 4 month old starter 2-3 days to fire up 100 ml of wort.

 

[Jazzafish]

I recently brewed one of my regular English milds and under pitched it with some WLP 005. I normally get a starter going but this time I just tipped the old slurry in.

The result was a completely different beer. I knew it would have some effect, but it was supprising. There were alot of dominating esters that took over from its normal malt driven flavour. Not as pleasant in my case.

In a wheat beer it would be great, but then again it all depends on the yeast.

 

[Jazzafish]

Just to be clear my underpitching experiment was an experiment, not a general practice!

 

[braufrau]

Pitching a 3-4 months old starter is a bad idea. There are minimal yeasts alive. Once yeast flocculates, they start dying off at a great rate. After 3-4 months, you would be lucky to have 1% of them alive.

So ... how long can I keep a starter in the fridge?
If I make a big starter and keep back 300ml before pitching ... how long will it
be useful? I only brew every 2 months. Can I keep it 2 months?

-braufrau

 

[pint of lager]

If you have good sanitation, and sanitation as close to sterile is needed when dealing with starters, you can easily use the yeast from 300ml, pour off the waste beer, add 100ml of starter, then step up when it is at high krausen. Do not try and pitch the old 300ml straight into a brew, it needs to be restarted.

 

[Keifer]

An interesting read, thanks all, i will post back whether i can pick any of the flavours mentioned, krausen is crankin and we'll see in a few weeks.

 

[braufrau]

If you have good sanitation, and sanitation as close to sterile is needed when dealing with starters, you can easily use the yeast from 300ml, pour off the waste beer, add 100ml of starter, then step up when it is at high krausen. Do not try and pitch the old 300ml straight into a brew, it needs to be restarted.

Thanks pint of lager ... that makes sense ... just like reculturing from a bottle!


-braufrau

 

[pint of lager]

Rules of liquid yeast work.

1. Use wort of sg 1.030 -1.040. for 1.040 use 100gms DME per litre. Aeration is important, you are aiming for healthy yeast growth, not beer production.

2. Be as aseptic as possible (as close to sterile as possible.) Take great care with very small amounts of yeast and wort transfer.

3. The smaller the quantity of yeast, the smaller the starter.

4. The older the yeast, the smaller the starter.

5. Once you have your small wort actively fementing, step up in scales of 10, for instance, 100ml is stepped up to 1,000 ml.

6. For ales you need an active starter of volume 5% of your wort. So if your batch size is 23 litres, you need a starter of 1.175 litres, most people aim for at least a litre. Lagers are slower to multiply and ferment, they need double, or 10% of your wort size. If making a stronger og brew, consider using fresh yeast slurry from a previous brew.

Aim to have your final step close to the volume needed.

7. Consider using a good quality yeast nutrient blend in your starters (not just plain diammonium phosphate, something that has lots of trace elements). Healthy parents have healthy children. Make sure you use the correct does, too much micronutrients can be harmful to your yeast.

8. Every time you work with yeast, sniff it and if possible, pour some into a glass and taste it. This way, you have an understanding as to whether the flavour/aroma is funky infected or funky hard working yeast.