Mash temp, pH & yeast attenuation

[Fore]

Mash temp: Lower in the temp range means thinner more alcoholic beer. Higher means less fermentable sugars, thicker body.
Mash pH: I believe sort of a repeat of the above (substituting "temp" with "pH").
Attenuation: Obviously certain yeast strains have different AA% ranges, but what is it that determines where in that range?

In my AG brewing adventure, I'm still going through different beers and styles; not yet tried to tie down one beer. But I'm getting close to that and worry a bit about repeatability, because I see such unplanned variation on my AA%. My recipe entered AA% is based on my own experience with the yeast strain, but honestly, it's a figure I have no idea where it will end. It seems completely random. What are the factors behind this?

 

[Sadfield]

I'm not sure pH has much effect on body, once you have the correct range for mash efficency, it looks after itself, mainly as a function of yeast maintaining an environment it tolerates but is hostile to other organisms.

Mash conditions should be easy to replicate. So, yeast pitch rate and health will probably have the biggest influence on repeatability.

 

[EddtheBrew]

I'm not sure pH much effect on body, once you have the correct range for mash efficency it looks after itself, mainly as a function of yeast maintaining an environment it tolerates but is hostile to other organisms.

Mash conditions should be easy to replicate. So, yeast pitch rate and health will probably have the biggest influence on repeatability.

Hi All ,
Yeast pitching rate and , TEMPERATURE are quite key to consistency ,
Cheers
Edd

 

[Fore]

To date I only use dry yeast; so same pitching rate every time. I guess though that sort of depends on how old the yeast is and how well it's been stored. I store it the same of course, but don't know what happened before it reached me.

Ferment temperature variation is not massive with me.

So the differences I'm seeing in different brews, would probably be matched recipe by recipe, I'm just seeing variations between brews? But when one Belgian style, mashed at 62C, finishes at 1.004 and another not so dissimilar, mashed at 63C, finishes at 1.013, is that just down to yeast selection (M31*2 in 1st, and s33+T38 in 2nd), or is something else at play?

I think what I'm trying to get at is, how do I know if it will finish 1.004 or 1.013?

 

[Sadfield]

Different yeasts will attenuate differently. Keeping a record of the % attenuation you get for each yeast you use will give you an idea of the attenuation to expect next time you use that yeast. Most brewing software will allow you to enter your attenuation figures and predict the final gravity/ABV.

When you say your pitch rate is the same with dry yeast, do you mean you are always pitching full packets? If so, whilst this works, it won't help to achieve consistent attenuation across different brews with the same yeast. Pitch rate should ideally be a calculation based on OG and volume. A 20L brew at 1.040 will require less yeast than one a 1.055.

Using a pitch rate calculator like this one will help.

http://www.mrmalty.com/calc/calc.html

Getting the pitch rate right has numerous other benefits.

 

[Braufather]

Do you have to pay for that calculator? Buy the app? Or is there a free version?

 

[Braufather]

Also out of interest, for the standard yeast packs -Wyeast smack pack for example, what would the perfect Match for 19 litres of wort be in terms of abv?

 

[Sadfield]

Do you have to pay for that calculator? Buy the app? Or is there a free version?

Should be free, although there are plenty of other calculators available free on the Internet. For dry and commercial liquid yeast, I just use the one incorporated into Beersmith.

 

[Sadfield]

Also out of interest, for the standard yeast packs -Wyeast smack pack for example, what would the perfect Match for 19 litres of wort be in terms of abv?

This is a difficult one to answer. WYEAST state the smackpack is good for upto 1.060 for a 19L (5 Gallon) batch, around 6-6.5% assuming an FG c1.008-1.013. However, that doesn't really add viability into the equation. Wet yeast is a live product and as a result age and storage can easily affect its condition. That's where calculators come in handy as they often take age into consideration.

Running some figures through a calculator.

A 2 month old smackpack can have around 54% viability, so pitching into 19L of 1.060 wort would be a significant under-pitch.

Conversely, pitching a freshly packaged, 100% viable pack into a weaker 1.040 wort could be adding almost double the cells required.

 

[Fore]

Different yeasts will attenuate differently. Keeping a record of the % attenuation you get for each yeast you use will give you an idea of the attenuation to expect next time you use that yeast. Most brewing software will allow you to enter your attenuation figures and predict the final gravity/ABV.

When you say your pitch rate is the same with dry yeast, do you mean you are always pitching full packets?

I've become familiar with Brewer's Friend pitch rate calculator recently, as I'm just starting to plan starters (done one so far). To date I've just been using one dry packet, two in the cases of very high ABV. I kept all my attenuation records, and that's what throws me, because, for example, 05 has given me anything between 68 & 94 AA%. The two beers were supposed to be roughly the same ABV, within 0.5%, but one ended up at 4.3% and the other at 7%. So I don't feel I have control over this aspect yet, and entering the AA% number in my recipe planner is just a big guess. I am in the process of getting a fermentation fridge to remove another variable.

What about this.... same beer mashed at 62C, then mashed at 69C. Given all other factors constant, will the 62C mashed wort drop to a lower FG?

 

[Braufather]

Sorry fore, I seem to be sidetracking your thread! Just one last thought here. As making a stater isn’t an option for me, and also to get an idea of what a perfectly pitched brew turns out like,

I am thinking of turning it on it’s head and tweaking the brew to match the yeast. So once my smack pack arrives, I plug the date into a calculator, or use trial and error to find the perfect original gravity for this particular pack at this age and amend my malt bill etc accordingly.

I never seem to plan ahead enough for starters and given I never have dme around it’s simpler to just pitch an extra pack if needed. Or repitch some slurry. However I’d like to do a few brews where I have pitched yeast at perfect levels just for experience.

Sorry fore! It in answer to your final question I believe the lower mash will result in a higher original gravity because more sugars in the wort so likely a corresponding higher finishing gravity too, all things being equal.

 

[Fore]

Oh god. I'm really on the wrong lines then. I always thought the lighter body came from lower FG. Got to rethink. I never thought mash temp would effect gravity; in my recipe calculator, mash temp is just a record, it has no impact on OG. Maybe my fermentation fridge will bring some clarity to this whole subject.

 

[Simonh82]

I've become familiar with Brewer's Friend pitch rate calculator recently, as I'm just starting to plan starters (done one so far). To date I've just been using one dry packet, two in the cases of very high ABV. I kept all my attenuation records, and that's what throws me, because, for example, 05 has given me anything between 68 & 94 AA%. The two beers were supposed to be roughly the same ABV, within 0.5%, but one ended up at 4.3% and the other at 7%. So I don't feel I have control over this aspect yet, and entering the AA% number in my recipe planner is just a big guess. I am in the process of getting a fermentation fridge to remove another variable.

What about this.... same beer mashed at 62C, then mashed at 69C. Given all other factors constant, will the 62C mashed wort drop to a lower FG?

Yes, i would expect a significantly lower FG with a beer mashed at 62 vs a beer mashed at 69.

I heard a nice explanation which suggested the mash temp, yeast attenuation and starting gravity are three variables you can tweak to get your desired results.

Keeping everything else the same if you start with a higher original gravity you will finish with a higher final gravity. Similarly, a high mash temp will lead to a higher final gravity and a low mast temp will lead to a lower final gravity.

When it comes to yeast attenuation the variation is really in the yeast's ability to metabolise maltirose. Low attenuating yeast will work through the gloucose and maltose in the wort but will get stuck on the maltirose. High attenuating yeast will carry on working and consume the maltirose too.

It is unusual to find one yeast strain like US05 varying so much as you've described but it might vary by 8 to 10% between a very high and very low mash temp.

One other thing to bear in mind is that low mash temps take longer to convert the starch so finishing the mash early might counter act the low temperature.

 

[Simonh82]

Oh god. I'm really on the wrong lines then. I always thought the lighter body came from lower FG. Got to rethink. I never thought mash temp would effect gravity; in my recipe calculator, mash temp is just a record, it has no impact on OG. Maybe my fermentation fridge will bring some clarity to this whole subject.

Mash temp probably won't affect OG, as long as you mash long enough for full conversion. It will affect FG as a lower mash temp will create a more fermentable wort and leave less residual sugars in the beer.

 

[Sadfield]

@Fore That's a big variation you're getting there. It'll be interesting to see your results when you get a stable fermentation temperature with the brew fridge. Yeast really doesn't like fluctuating temperature.

@Braufather Getting the pitch rate right reduces the potential for problems and off-flavours and promotes consistency. Over or under pitching can still produce a good beer. It's worth trying your experiment, although it may not result in a conclusive result.

As for varying mash temperature, it doesn't so much change how much sugar is extracted from the mash, it changes the type of sugar in the wort. Cooler mash temps result in simpler sugars that are easier for yeast to process. Hotter mashes leave more complex sugars that yeast struggle to process.

EDIT: Sorry, I see @Simonh82 has already covered most of this. I got side tracked.

 

[IainM]

I found this article useful for clearing things up.

 

[Braufather]

There seems to be a lot of difference in the calculators and they all seem to call for a lot more than the manufacturers recommend.

Brewersfriend for example seems to say you you would need 133 billion cells for a week beer with OG of just 1038 for 19 litres. So a smack pack with 100 % viability has 100 million thats 33 billion short so it’s says you need a starter? For a 1038 brew?

Even more crazy is it says that a 20 day old pack is still a few billion short on cell count for a OG 1025 beer! Surely not

https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/


Up until now I used it the rule one one pack for brews under 1060 and two packs for over. The one time I repitched slurry it worked really well but wasn’t that scientific, so could have been luck.

I’ve used starters for big beers with mixed results, certainly no better than pitching two packs in my limited experience.

 

[Simonh82]

There seems to be a lot of difference in the calculators and they all seem to call for a lot more than the manufacturers recommend.

Brewersfriend for example seems to say you you would need 133 billion cells for a week beer with OG of just 1038 for 19 litres. So a smack pack with 100 % viability has 100 million thats 33 billion short so it’s says you need a starter? For a 1038 brew?

Even more crazy is it says that a 20 day old pack is still a few billion short on cell count for a OG 1025 beer! Surely not

https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/


Up until now I used it the rule one one pack for brews under 1060 and two packs for over. The one time I repitched slurry it worked really well but wasn’t that scientific, so could have been luck.

I’ve used starters for big beers with mixed results, certainly no better than pitching two packs in my limited experience.

The yeast pitch calculators generally recommend a pitch rate of 0.75m cells per ml per degree plato for average strength ales. The yeast manufacturers recommend a pitch rate of roughly half that. The lower pitch rate will likely still ferment your beer but it may increase the chance of a higher final gravity or even a stalled fermentation. In reality the manufacturers guidelines will probably work fine in most cases, especially if you have well oxygenated wort in nice sanitised fermentor and the temperature is a good one for the yeast. The pitch rates that are recommend by the calculators are probably a good insurance policy though.

 

[Fore]

OK, so finally it seem like I was on the right track after all. So a higher mash temp in the same recipe, all else equal, should in theory leave more residual unfermentable sweetness and thus higher FG.

As it turns out, I have a brew on which is an almost identical copy of the same I've done before. Happens to be the first time I have done the same AG twice. My final SG was only 1 point out from my previous effort. Same yeast. The only variable was the mash temp (and the hops, but I doubt they play a part in FG, so irrelevant), so it will be interesting to see where the FG ends up. Last time it finished at 1.004. It needs another week or 2.