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Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > Yeast & pH - Slow Start on Acidic Wort
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Old 02-24-2011, 05:32 PM   #1
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Default Yeast & pH - Slow Start on Acidic Wort

I was bored the other day and all my 3 and 5 gallon carboys were full. I decided to do a 1 gallon test batch to test an apricot syrup I wanted to use in an upcoming brew. I only did a partial mash, so I didn't worry about checking pH as I normally do on all grain brews.

I used an apricot syrup by Maple Grove Farms, which is organic and has no preservatives. I used yeast nutrient in the wort and aerated extensively. But for some reason, after 28 hours, I had good flocculation but absolutely no active fermentation. I always get a good active fermentation within 12 hours, so I started to trouble shoot.

I went back to the apricot syrup found malic acid as an ingredient. I tested the wort and the pH was slightly lighter than the bottom end of my test strip range, around 4.4.

I added baking soda and calcium carbonate to get the pH to about 5.2-5.4. Within 4 hours, the fermentation started up.

I've read alot about pH for mashing purposes, but I've never seen much on pH and how it impacts yeast. From this lone test, it appears pH had a significant impact on my yeast's ability to begin fermentation. Good to know if I ever use this syrup!

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Old 02-24-2011, 05:34 PM   #2
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anyone know of any information on yeast and ph? I'd like to study up a little more. I am also a bit concerned that the baking soda and calcium carbonate may have other flavor impacts on my brew....

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Old 02-24-2011, 05:51 PM   #3
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I've read that yeast grow best in ph 4-6 and can survive down to ph 2, maybe they needed to multiply and were a tad "retarded"? The maltose falcons have alot of information regarding yeast on their site. http://www.maltosefalcons.com/tech/y...-and-practices

Edit: Looking further on their site, this is where I read it, just scroll down to PH, there is a small section there.

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Old 02-24-2011, 06:08 PM   #4
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thanks for the link! as far as variables go, i had everything pretty controlled (good oxygen, healthy pitch rate of pacman yeast, good flocculation, constant 65 degree temp). But the lag time between pitch and active fermentation was way off from my normal brews.

i'm guessing that 32 hour lag and my emergency additions of baking soda and calcium carbonate will impact the beer negatively. i'm very glad i decided to do a 1 gallon test before jumping into an expensive batch!

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Old 02-24-2011, 06:20 PM   #5
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There was some very beneficial info in that link related to my issue, but it leaves me with more questions:

"pH. The last factor to affect yeast growth is pH (a measure of acidity). Yeast grow well at acidic pHs. They grow best between pH 4 to pH 6. Normal wort is acidic with a pH near 5.2. During growth and fermentation the pH drops to about 4.1-4.2 and in some cases even lower. The further acidification of the wort helps to prevent bacterial infection. (Most bacteria cannot tolerate acid pH). Yeast can survive at very low pH, as low as 2.0. This is the basis of acid washing where the bacterial load of a yeast slurry is reduced prior to repitching by lowering the pH to 2.2. Most bacteria will be destroyed at this pH while a good percentage of the yeast will survive. Interestingly, diluted unfermented honey is more acidic than wort and the production of more acid during fermentation actually slows down its fermentation. To make matters even worse most meadmakers add acid blend to the honey. Although the acid does help to balance out the flavor, it will inhibit fermentation and therefore should only be added after fermentation is complete. In fact some meadmakers will add a small amount of calcium carbonate to buffer the acidity and raise the pH. This can significantly accelerate fermentation. I have successfully fermented a mead out in a week using this method (and a good healthy supercharged starter)."

First, I never thought that the growth of the yeast may have made the wort more acidic. So, when I added alkalines to get the pH from 4.6 to 5.2, I may have disturbed an otherwise normal occurrence.

Second, like the mead illustration in the quote, I added honey AND apricot syrup with malic acid. Basically, I added a double dose of acids to my wort. But the author did as I did by adding alkalines to aid in the start of the fermentation process.

Did I do the right thing by bringing the pH up when I did?

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Old 02-24-2011, 06:29 PM   #6
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Here is an excerpt from Kaiser's How pH Affects Brewing article that may help:

Quote:
Nutrient uptake by yeast
Shortly after being pitched into fresh wort yeast will start lowering the pH of the surrounding medium (i.e. beer). This is the result of ammonium ion and amino acid uptake, secretion of organic acids [Briggs, 2004] and most importantly a proton pump which moves H+ ions from the yeast cell into the beer. By doing so the yeast also raises its internal pH. This proton pump is very important to the yeast and it is the most abundant protein in its cell membrane [Briggs, 2004]. The resulting pH gradient through the yeast's cell wall facilitates the uptake of nutrients like maltose.

Maltose uptake is a proton symport process through the cell membrane. The proton concentration outside the cell is greater (lower pH) than inside the cell (higher pH) and therefore a natural gradient exists which encourages protons to flow from the outside to the inside of the cell. Though the use of a symporter, a cell membrane protein, maltose can “piggy back” on the flow of protons into the cell. This is one of the reasons why yeast cells do better in an acidic environment and have means of lowering the pH.

The ability of yeast to lower the beer’s pH is important for healthy and low yeast stress fermentation and is one of the reasons why sufficient pitching rates are important and why it is better to step up starters rather than starting a small amount of yeast in a large starter. The more yeast cells that are working on lowering the pH the faster the pH will be able to drop.

As yeasts age, starve or otherwise loose their vitality, it becomes increasingly difficult for them to pump H+ from their cells into the beer. After all, this goes against nature’s desire to equalize everything and therefore takes energy. The result is a slight rise of the beer pH after primary fermentation. The pH can rise more significantly if the beer is not taken off the yeast before a large number of yeast cells start to autolyze.
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Old 02-24-2011, 06:39 PM   #7
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so it seems like the drop in pH to 4.6 may have been normal and maybe i should not have tried to bring it back up to 5.2?

but something gave me a very long lag and the yeast did respond rather quickly to begin actively fermenting after i brought the pH up to 5.2. it will be interesting to taste this beer once it finishes to see how the flavors turn out.

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Old 02-24-2011, 06:50 PM   #8
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I don't think this was a "very long lag". As you said this is not one of your normal brews, I would think the thing that changed was the governing factor, the apricot syrup, however what was the OG of this? Was it higher than your typical fermentations?

Personally I don't start worrying about any fermentation (Or lack thereof) until after day 4, I find most fermentations to differ in some way from batch to batch, however I don't typically brew alot of the same brews in concession.

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Old 02-24-2011, 06:55 PM   #9
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I'm not sure if the low-ish pH was due to the malic acid and honey or if it was due to the yeast doing their thing. It may be that it was going to take off anyway.

It seems that if the pH is too low then the yeast might struggle to establish that pH gradient required to get the sugars into the cell...but I don't know how low is too low. 4.4 doesn't seem like it would be too low, I would think berliner weisse (for example) starts lower than a typical beer but I've never brewed one (intentionally ).

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Old 02-24-2011, 07:17 PM   #10
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I've never seen yeast impacted by pH unless it gets down to below 3.5 or even around 3. This pretty well only happens in mead.

If your pH was below 3.5 and you added enough bicarbonate to get to 5.4, that would have been a lot of bicarbonate and it will have a large impact on flavor.

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