Why Phosphoric Acid is Flavor Neutral

[ajdelange]

This came to me the other day and has been in a couple of posts already but I think this insight is important enough to deserve its own thread if not Sticky status.

Phosphoric acid appears to be flavor neutral because, after it has done its job of yielding up a proton, it is changed to biphosphate ion and mash already contains a lot of that. According to Briggs malt is 0.4% phosphate as phosphorous. Converting that to as biphosphate ion we'd have 1.25% meaning that 1 kg of malt contains 12.5 grams of H3PO4- which is 129 mEq. Suppose we mash a kg of this malt in 3 L of water of with calcium hardness 7 mEq/L (140 ppm as CaCO3). 1/3.5 th of this calcium, 7*3/3.5 = 6 mEq would precipitate as apatite, Ca10(PO4)6(OH)2, taking 6*6/20 = 1.8mEq of H2PO4- with it leaving 127 mEq in the mash tun.

Now further suppose that the water is quite alkaline to the extent of 3.33 mEq/L (166.7 ppm as CaCO3). The 3 L of water thus contain 10 mEq of slkalinity. In most beers we need to neutralize 90% that with some acid or another amounting to 9 mEq. If we chose phosphoric acid for this we will need 9 mmol as each phosphoric acid molecule yields up 1 proton when added to mash at typical mash pH and converts to 1 mmmol biphosphate: H3PO4 ---> H+ + H2PO4-

For this nominal calculation, which represents fairly hard, alkaline water, in treating the water to remove alkalinity we are increasing the biphosphate content of the mash by
(127 + 9)/127 or 7%. As a detectable change in a biological stimulus usually requires a change in the stimulus of 25% or more we don't notice a flavor change when we add phosphate to mash.

So while it appears to be true that phosphoric acid is less strongly flavored than, for example, lactic acid in solutions of equal pH, the main reason we don't taste phosphoric when we add it is because there is already so much of it there.


Briggs, Denis E Malts and Malting Blackie Academic and Professional, London, 1998 p 191

 

[berndawg84]

Great post. From what I've read, phosphoric acid seems to be the best thing to use to lower mash pH, since lactic acid does have a stronger taste...is that right? Still trying to learn more about water chemistry.

 

[ajdelange]

Yes, if you make up solutions of water at the same pH with lactic and phosphoric and ask people which tastes more acidic they will pick the lactic BUT the main reason you don't taste a phosphoric addition in a mash is because you are adding proportionally only a small bit to the amount that is already there.

 

[mabrungard]

Don't discount lactic acid for taste reasons. When used at low to modest concentrations, I don't believe that most tasters would find any flavor from lactic acid or acid malt. Another consideration is that lactate is a yeast nutrient.

It is in high alkalinity water that lactic acid can be problematic to beer taste. Then moving to phosphoric acid is necessary.

 

[ajdelange]

Wouldn't discount it for a minute as I actually like the flavor whether it be from liquid acid, sauermalz or sauergut, esp. from sauermalz.

 

[techbrau]

Wouldn't discount it for a minute as I actually like the flavor whether it be from liquid acid, sauermalz or sauergut, esp. from sauermalz.

I agree, and think that biological acidification is a big part of getting the authentic flavor of German lagers.

If you like sauermalz, you have to give sauergut a try. It tastes even better to me.

Nowadays I keep a permanent culture going in mason jars. I use about 2/3 of it on each brew, and refill it with fresh wort from the mash (diluted to 10-11 plato if needed). I incubate it for about 24h in a sous vide bath at 118F, then throw it in the back of the fridge. It will keep for a month or more until your next brew day.

I made the mother culture by doing a small 3 liter mini mash in a pot on the stove (LODO, of course) to make a 10 plato wort, filling the mason jars, cooling to 118 F, dropping the pH to 4.5 with approx 20 g/l raw acid malt, and then inoculating it with approx 20 g/l raw pilsner malt.

You need to titrate it to figure out exactly how much acid you have, but you will generally reach about 0.8% acid after a 24h incubation. At that concentration it takes 60 ml sauergut for every kg of malt in your mash to drop by 0.1 pH, and 30 ml to drop by 0.1 in the boil.

I like to drop to 5.2-5.3 in the mash, and then add a second sauergut addition at the end of the boil to hit 5.0

There's a lot more to acidification than simply hitting a pH number. Biological acidification brings a whole host of other benefits that you don't get by simply using technical acid:

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2004.tb00199.x/pdf

But honestly, the flavor improvement of sauergut over sauermalz - especially for light lagers - was all it took to convince me that maintaining the culture was well worth the effort.

 

[ChuckS1]

It is in high alkalinity water that lactic acid can be problematic to beer taste. Then moving to phosphoric acid is necessary.

I'm new to water chemistry. What's the definition of "high" for alkalinity? My water report from Ward Labs has my total alkalinity at 100 and HCO3 at 122.

 

[ajdelange]

I call anything below 1 mEq/L (50 ppm) low and is the region in which we'd all like to be as it is easily manageable with sauermalz which is, as is plain from #6, much easier to manage than sauergut and still gives some of the flavor benefits. One to perhaps 3 mEq/L is still manageable with acid including lactic unless you are sensitive to the taste and don't want it. I guess I'd consider above 3 high to the point where you might want to consider decarbonation rather than neutralization with acid but this recent insight has me rethinking that as it appears we can neutralize obscene levels of alkalinity (10 mEq/L ~ 500 ppm) with no effect other than increasing mash phosphate by 21 %

 

[day_trippr]

Well, I can testify that there is a limit to this "flavor neutral" thing.

My well runs "hard" enough I had to go with an RO system if I ever wanted to brew anything light. I committed to that reality after the two successive SRM ~3 AG brews I tried required so much phosphoric acid (per Bru'n Water) that it was clearly noticeable as a mid-pallet off-note.

I love my RO system...

Cheers!

 

[ajdelange]

Obviously there has to be some limit. Malt may be 1% phosphate and the rest mostly starch but if it were 10% phosphate and 90% starch it would probably taste funny. OTOH are you sure that mid palate off note wasn't calcium?

 

[Homercidal]

Yep, I use RO even though I could probably balance out with PHOS. I prefer to use as little additive as necessary, and then tweak as I want. If I'm brewing a really dark beer like a stout I might keep 50% of my tap water. Probably 80% of my brews are made with RO water (Or distilled bottled water.)

 

[ajdelange]

I really am in sympathy with the less is better philosophy expressed in #11 and thus want to make it clear that I'm not suggesting that people stop using RO or use it less. IMO RO is clearly the best way to go as you are in complete control. If you neutralize with phosphate or any other acid you must titrate or calculate the amount you need to offset water alkalinity. With RO you don't as the water's alkalinity is trivial compared to the malts'.

 

[SirCasio]

I'm new to water chemistry. What's the definition of "high" for alkalinity? My water report from Ward Labs has my total alkalinity at 100 and HCO3 at 122.

Thanks, AJ for describing what you think is low and what is insanely high...however, I have the same question as Chuck, and what level would it be considered "high enough" that using Phosphoric Acid over Lactic Acid (or Sauermalz) be recommended?

 

[ajdelange]

Unfortunately I don't think there is an answer for that though I'm sure you can elicit lots of opinions. Mine, FWIW, would be to use RO water and only enough lactic to handle the alkalinity of your malt. I would not use phosphoric. Please realize that I am not telling you that this is what you should do. My practices are dictated by the kinds of beers I brew/drink and my personal tastes. Eventually those factors will inform what you do in your brewing.

 

[day_trippr]

Obviously there has to be some limit. Malt may be 1% phosphate and the rest mostly starch but if it were 10% phosphate and 90% starch it would probably taste funny. OTOH are you sure that mid palate off note wasn't calcium?

No idea what it was but as I've brewed the exact same recipe using RO with additions and it came out great I'm reasonably confident it was fallout from the phosphorous acid. Literally the only thing different was the water.

Also that character was never present in dark beers that required much less acid...

Cheers!

 

[JDL]

Day_trippr,

Out of curiosity could you post the amounts to water you used? Always good to know where other people noticed a flavor adjustment.

Thanks,
Jeff

 

[day_trippr]

Our home used to be on a private water system but it folded, which required all 200-something homeowners in the covered area to drill their own wells.
Fun times

I'd been trying to get a handle on things since. Got the Ward test, used Bru'n Water, brewed some stouts, porters, esbs, even a Trappist ale, didn't notice anything aside from the amount of acid I needed to use was way higher than before.

Then the Cream Of Three Crops came up in the rotation.
Waterloo. Literally.

For strike and sparge volumes of ~ 7 and 9 gallons respectively I needed 34 ml and 31 ml of 25% Phosphoric Acid to hit a calculated mash pH of 5.24 and sparge pH of 5.5.

The result had this weird mid-palate thing that I immediately found off-putting, a strange minerally character that had some linger to it, enhanced by an apparent tartness that shouldn't have been there considering the bland recipe.

Somewhat interestingly, my wife didn't notice it, and one of my sons had to be prompted to even consider if there was anything there. But I'm my worst critic and that batch was definitely off - by a lot, compared to previous batches.

That was the end of that. I installed an RO system in my shop and with a TDS down around 7-8 I need barely more than one milliliter of acid to bring the sparge water for a 10 gallon batch to 5.5. I've done a couple of pales, dipas and a Trappist since the RO went in without any issues. Once I've done another CO3C I'll know for sure I've buried that problem for good...

Cheers!

[edit] Forgot these from the Ward test:
TDS 322
Na 30
K 4
Ca 69
Mg 11
Total Hardness as CaCO3 218
SO4-S
Cl 84
CO3 <1.0
HCO3 178
Total Alkalinity CaCO3 146

Train Wreck City

 

[amschind]

Two questions:
First, if the phosphorus is biologically available (and since HnPO4 buffers are what most folks use for microbiological growth media, I assume that they are), won't the yeast incorporate some fraction of the phosphorus into the multitude of biological molecules which need phosphorus (DNA, ATP, et c)? If it does, then that fraction of the added phosphorus will wind up in the yeast cake, which would only affect taste if you're into homemade Vegemite.
See below; I try to answer my own question for fun.

Yeast Growth In the Absence of Phosphorus
While this isn't exactly what we're discussing, figure 1 does illustrate the optimal biologically available phosphorus concentration for S. cerevisiae (~75 ug/ml) beyond which additions don't affect growth.

Wort Composition Review

If we believe this paper (bottom of page 51) we get 620-1000mg/L for the average wort.

Yeast per Liter of Wort

This paper gives a rather broad range, but seems to form a Bell Curve with an eyeball mean of 10 gm yeast/L wort (look at fig 2, as fig 1 is in a lab setting and fig 2 is from a real brewery). Trying to get from 10 gm/L to the amount of phosphorus tied up in yeast is challenging (versus simply (10,000mg yest/L wort)*(2ug P/mg yeast)= 20mg P in yeast/L wort) because the first paper pretty clearly demonstrates that yeast will take up more phosphorus in a linear and then supralinear fashion as more is available, even after reaching an optimal media P concentration for growth. Note that both papers measured yeast as "Wet pressed yeast", which the growth paper defines more clearly as roughly 75% water. Given how inexact these calculations are, I don't think that differences in how much water the researchers squeezed out of their samples is likely to be a major source of error.

The initial amount of yeast is a challenge as most people list pitch rates in terms of cells/batch. The paper itself describes seeding with 500 mg of wet pressed yeast per liter of wort, and to avoid laborious and likely incorrect conversions between dry yeast pitch rates in mg, wet yeast mg per mg of dry yeast, cells per mg, and variable pitch rates, I am going to stick with what the paper used (if someone has already or can verify this, please jump in).

If we assume 1 L of wort for simplicity at 700 ug/ml P and 500 mg of yeast pitched carrying with them 2.5 ug P/mg yeast, we can proceed as follows:
(500mg yeast)*(2.5ug P/mg yeast)=1.25mg P in the yeast starter
(1L wort)*700mg/L=700mg phosphate (I+O)
(6000mg peak yeast/L)*(1.8ug P/mg yeast)=11 mg P in the yeast
(9500mg peak yeast/L)*(2ug P/mg yeast) = 19 mg P in the yeast
(9500mg peak yeast/L)*(4ug P/mg yeast) = 38mg P in the yeast
(9500mg peak yeast/L)*(6ug P/mg yeast) = 57mg P in the yeast (most likely real world result)
(18000mg peak yeast/L)*(2ug P/mg yeast)=16mg P in the yeast
(18000mg peak yeast/L)*(4ug P/mg yeast)=72mg P in the yeast

So, we get a range of 10 to 72 mg of P tied up in the yeast, with my guess at the most likely real world result at 57 mg P tied up in the yeast, a whopping 91% of the phosphorus is untouched (650mg-57mg=593mg; 593/650=91%) and is not removed by the yeast.

I will now rephrase this in real terms to see how it affects my situation.
Previously, I used Bru'nWater to calculate a 7.5ml 85% H3PO4 addition to 15 gallons of water; that works out to ~190 mg/L H3PO4. Compared to the 600-1000 mg/L range seen above, I should still be well within the middle of that range. The yeast will remove anywhere from 20-80 mg/L of the phosphorus, which won't appreciably affect the result.

My second question relates to lactate and its utilization by yeast in fermentation/wort conditions, but that one may be a little harder to answer using google.

 

[ajdelange]

Yes, yeast will definitely incorporate some phosphate as part of the additional biomass produced in a healthy fermentation. What are most yeast nutrients made of? DAP.

Yeast will not consume lactate AFAIK. In metabolic processes the organism transfers electrons to sugars producing reduced state products like lactate and ethanol. Though each reaction in the pathways is reversible the conditions are not favorable for them to run in reverse during fermentation. In the second place yeast, at least the ones we use in brewing do not, to my knowledge, have a lactate producing pathway to run in reverse even if conditions were right.

The preceding is my opinion based on common sense, not specific knowledge of lactate metabolism (or catabolism in this case) in yeasts.

 

[amschind]

Though each reaction in the pathways is reversible the conditions are not favorable for them to run in reverse during fermentation. In the second place yeast, at least the ones we use in brewing do not, to my knowledge, have a lactate producing pathway to run in reverse even if conditions were right.

I found this:
Yeast Growth On Lactate

The introduction summarizes the ability of yeast to grow on lactate, and mentions a lactate dehydrogenase that is expressed under anaerobic conditions. I agree that a molecule used as a surrogate electron acceptor likely wouldn't be metabolized in the absence of oxygen, but it appears that yeast can use it as an energy source under aerobic conditions.

In metabolic processes the organism transfers electrons to sugars producing reduced state products like lactate and ethanol. Though each reaction in the pathways is reversible the conditions are not favorable for them to run in reverse during fermentation.

I think that this is likely the explanation, namely that the aerobic conditions expire (i.e the yeast uses all of the oxygen) well before preferable energy sources like sugar are consumed.

Anyway, not sure that this is of any practical value, but understanding the process is part of the fun. Brewers are the founders of molecular biology.

 

[ajdelange]

The introduction summarizes the ability of yeast to grow on lactate, and mentions a lactate dehydrogenase that is expressed under anaerobic conditions.

Anaerobic?

I agree that a molecule used as a surrogate electron acceptor likely wouldn't be metabolized in the absence of oxygen, but it appears that yeast can use it as an energy source under aerobic conditions.

It is well known that under the proper aerobic conditions yeasts can respire (transfer electrons to oxygen) and thus use ethanol as an energy source so I guess I'm not surprised to hear that they can do so with lactate as well.

But aerobic conditions are not those of fermentation so I don't think you need worry that if you add 5 mL of lactic acid to a mash that the yeast will consume 2.5 mL of that.



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