November 3, 2024 - 4:56am
pH and BF when starting nb is high
Hi! I'm new to the pH world and could use some guidance. I just mixed my dough (50/50 bread flour-Semolina Rimacinata), and the pH is 5.8.
My understanding is that I should aim for a pH drop of about 1.0 to end bulk fermentation and start shaping. However, I also read that I should aim for a pH between 4.1 and 3.8 to end the bulk phase.
With my starting pH so high, should I aim for a 1.0 drop or wait until the pH reaches that 4.1–3.8 range? I know I could use some other cues to determine when my bulk is done, but I'm really not used to working with semolina, that's why the pH could be very useful here.
Thanks in advance for any insights!
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Also very interested in this.
Would be great if those who have discussed this in past posts could link through to some of the more insightful postings/threads.
Also was wondering if, just for ball park view of the change in acidity of the dough one can use soil ph meters rather than the much more expensive food specific ones.
I have been measuring pH in just about every sourdough bread that I have made the past couple of years. I’m an engineer (retired with some extra time on my hands) and have been looking for that easy way to tell when BF is done.
Sad to report, I haven’t found it yet. I think I understand why.
I have also read that a drop of 1 pH point works. I tend to make my breads with about 40-50% whole grains, and if I let the pH drop a full point then my dough will be soup. You may have read that the presence of bran, as indicated by a high ash content, has a buffering effect on the acid produced by the LaB. It is not a true buffer, in the chemical sense, but it does slow the drop in pH. For example, my doughs typically start at around 5.6-5.7 pH, and I have found the BF to be done at around 5.2-5.3. During the shaping, divide…preshape…rest…shape, it will drop an additional 0.1-0.2 pH. If retarding the dough in the refrigerator overnight it will drop another 0.1-0.2 pH.
I don’t have enough experience measuring a dough made with 100% white flour, so I don’t know if the 1 pH rule will work for that. The main takeaway, for me at least, is that there are too many variables that affect the dough, and pH is another tool to help understand the process. If you consistently use the same or similar formulas for your dough, as I do, you can use pH as a guide. But I would never depend on it exclusively.
-Brad
[Edited] Your question was about 50% durum flour, and unfortunately I do not have any data on that. However, I have added 25% durum with the same results.
Very interesting!! I had no idea about that buffering effect...And very disappointing at the same time, I was hoping for a magic formula, but apparently I can forget about that :-)
Still, very useful to know that a BF can be done at such high pH readings!
Thanks a lot for sharing your experience!
I hope it is useful.
Maybe others have had different experiences and that would be interesting, too.
-Brad
I don't think that the ending pH tells much about how well fermented the dough is. Partly that's because the end pH depends on the starting pH, and that depends on the pH of the starter at that time and the ratio of water to starter. Buffering by bran, etc., can also play a role in moderating pH changes, as mentioned by Brad.
I have noticed that my starters tend to bottom out around pH 3.9 (they will go a little lower if you wait long enough). But at that point, they will be more than ready to be refreshed.
I haven't made pH vs time measurements for bread dough very often, but I have seen end pH values for sourdough breads in the range of roughly 4.1 to 4.5 or so. White flour yeasted doughs seem to start out around pH 5.2 - 5.5, and the pH will not have declined much by the time bulk fermentation is done.
I think that pH readings on dough would be more helpful when you need to have your dough be fairly acidic, as for high-rye breads when you need to avoid starch attack.
You can get a rough feel for the starting pH values by looking at the concentration of H2 ions in the water in the dough, since the pH measures that concentration on a logarithmic scale. Let's start with a 100% hydration starter and use that at 20% baker's percentage. Let the dough hydration be 2/3 = 67%, Since half the starter is water, so the baker's percentage of starter water is 10%. The new concentration of H2 ions will be 6.7 times as high as the starter. pH uses the logarithm base 10, and log(6.7) = 0.826.
So if the starter pH was 4.0, the new dough should read about 4.8. That's in line with measurements I've made. (We can neglect the pH of the flour itself because at say 5.5 it's small compared with the starter).
Sure, over-simplified, but it gives us the idea.
Another way to think about the importance of the endpoint pH in the fermentation process is to ask what's more important to the fermentation, yeast or LAB? For dough properties, I think most people would say the yeast. For flavor, of course, it's the LAB. Almost all of the pH changes come from the LAB, but the yeast's behavior determines the endpoint of fermentation. The acidity does affect the yeast behavior, but as far as I know (maybe not very far) that's a secondary effect.
TomP
I shouldn't add this ..... but acidity does have an effect on yeast. Things work out in the end .... if there is one. Enjoy!
I'm confused about your pH calculation. The concentration of H+ ions decreases as the pH increases from 4.0 to 4.8 (pH = –log[H+]).
Also, because the acids of interest (lactic and acetic) are weak acids, the dilution does not have as large effect on pH as with strong acids. For example, pH of lactic acid at different concentrations:
Hydrochloric acid would show a full pH value decrease for each 10-fold increase in concentration (pH 3 to pH 1 at those concentrations).
I think we both have it the right way around. Mixing the starter into the rest of the dough ingredients reduces the concentration so the pH goes up. Remember, I wrote that I oversimplified things!
How does the pH go from 3 to 1 for a 10-fold increase in concentration? Log(10) = 1, so the step should be one pH unit, not two.
That's why I was confused. Although, dilution alone will not produce such a large change in pH, as the example of lactic acid showed. There other effects that contribute to the magnitude of the increase.
The example for HCl was for each 10-fold increase in concentration, from 1 mM to 100 mM.
Fascinating!! I definitely need to percolate all of this, as it is way more complex than what I suspected...Thanks so much for your input!
Is it possible that the buffering effect is actually chemical? The ash composition of wheat flour is inorganic materials, mostly phosphorus, magnesium, and calcium. Magnesium and calcium compounds tend to be alkaline and might be the source of the buffering.
I haven't yet found a description of how these elements are incorporated in the wheat kernel, so I'm just guessing how they might interact with acids.
Also, the bran layer contributes additional non-gluten-forming protein that probably has sites that can be protonated to buffer some of the acids.
Forgive me f this is a little hand waving, my chemistry education goes back a few decades, but I think this is generally the way it works. A true chemical buffer is composed of an inorganic salt dissolved in water. A buffering solution is designed to hold the pH at a specific level upon the addition of more acid. To do this the salt is selected based on specific acid or acids.
In a sourdough, we know the acids are lactic and acetic, but the salts are whatever comes from the grain. It will neutralize (I use the term loosely) some of the acid but will not keep it at a specific pH.
This is all I meant by not “in the chemical sense”.
-Brad
I should make some pH measurements on 100% white flour sourdough with low ash. Looking back through my notes, I made measurements on white starters but not on the increase of pH when mixing starter into all white dough.
Tom,
That would be informative. Please let us know what you find.
-Brad
Here's what I measured. The flour was Gold Medal App-Purpose Unbleached. The loaf used 300g of the flour, hydration was 70% plus a point or two for the starter, and the starter baker's percentage was 30%. Salt was at 2.3%.
Here's some data. I didn't include the kind of kneading or S&F at the measurement breaks.
10:20 AM starter - 3.86; starter + all the water: 3.92
10:35 4.9 # 4.85 - 4.95 - after rough mix; depends on location
11:05 4.9 # 4.85 - 4.95
11:50 4.81 # 4.8 - 4.83
1:55 4.45 # Little variation
2:35 4.3 # 4.29 - 4.32
3:00 4.21 # 4.2 - 4.22
3:40 4.12 # 4.09 - 4.12
4:40 4.03 # 4.0 - 4.06
5:48 3.90 # very little variation
6:55 3.80 # a few places ~3.75
7:00 PM - shape
7:40 - start bake; preheat 450 deg F; steel; initial steam. final baking temperature 400 deg F.
8:40 - end bake
I was surprised by how much variation there was from one place to another in the dough, especially in the earlier measurements. There was enough variation that one shouldn't look at the exact values too hard.
I fermented too long because I wanted to know how the pH changed as it got down to and below 4.0. I should have stopped bulk ferment 1 1/2 or even 2 hours sooner. At shaping time the dough was too soft and extensible and it took a lot of stretching, folding, and re-rolling to build up enough elasticity that the loaf could hold its shape during proofing. Probably because the fermentation was too long, the crust color came out a pleasant straw yellow rather than the darker reddish-brown I usually get. I won't know about the interior until tomorrow morning.
Here is a graph of the pH data. To emphasize the fuzziness of the pH values, I have plotted them with the style used by the XKCD comic/science/technology/sociology/I-don't-know-what-to-call-it web site.
ph-sourdough-ap.png
Love your sense of humour Tom with your choice of chart.
Wonder if the way to measure is to probe a small aliquot instead of the big dough body. Almost certainly less accurate, but wonder if that will be relevant to the final breads or not.
-Jon
The fact that the mixture does not hold at a specific pH is may be because the flour/dough is an imperfect buffer. It may have limited capacity to buffer the acids produced. There is also the issue of the acids "finding" the bases in the viscous dough and reaching a true equilibrium.
FYI—buffers need not be composed solely of inorganic salts. There are several buffer systems that use organic molecules, usually amines and/or organic acids.
The only magic is your nose and your eyes. That's all ya need. Enjoy!
I have monitored pH in bulk on and off for quite a while. I had high hopes that this would be a reliable indicator of bulk "doneness".
Unfortunately, at least for me, this was not the case. I think one of the problems is that every baker has a different take on when bulk is complete in terms of % rise. I usually look for an increase of 40-50%. This gives me good oven spring, hopefully a good ear and open crumb. Others prefer a much bigger volume increase. This may give more flavour development, but perhaps at the expense of those previous parameters I just mentioned.
Of couse both these approaches must differ in the pH drop that is achieved.
Another problem, at least in the UK, relates to fortified flour. ALL UK wheat flour (except wholemeal) is fortified with calcium carbonate. Although I have never seen it reported, my conclusions are that the mildly alkaline calcium carbonate tends to neutralise the lactic acid produced in fermentation, so it is very difficult to achieve crumb pHs of 4.0 - 4.1 that others report, unless you ferment excessively.
For the record, typical values for me are bulk initial pH 5.60, bulk finish pH 4.75 and crumb pH 4.55. I also find that bulk initial pH can be influenced by quantity of levain, levain pH and levain type, eg wheat or rye. But a low bulk starting pH does not necessarily give a low bulk final pH.
Lance
Thanks a lot, Lance. I think I'm starting to get the idea...I'll keep experimenting, while keeping all of this in the back of my mind. Again, thanks a lot, your input is greatly appreciated!
I was interested in ph, not as a panacea, but more an early warning indicator that the BF dough was getting too acid and therefore the gluten might be at risk of deteriorating, particularly where wholemeal flour is involved and enzymatic activity and fermentation can get away before there is a significant increase in volume.
Obviously different flours have different abilities to withstand acid and enzyme deterioration (e.g. high W number flours), so that also has to be factored in, but it would be useful, like an aliquot jar can be for volume, to have an idea how acidity is developing, even if not going by an absolute number.
Interesting Lance, you're influencing my thinking on whether I should get a better pH meter or not.
Have you ever made panettone? Isn't that what you really need the meter for?
-Jon
Don't get me wrong, Jon - I still find a pH meter useful. It's handy for monitoring starters and levains and I do check my dough and crumb pHs quite regularly.
I was really making the point that, for me, pH is not something I would use as a break point for the end of bulk.
I also make some soft cheese now and again and it is useful for that.
And, as you say, very useful when making panettone.
Lance
I was recently gifted a food pH meter and have been taking some measurements just for fun. I did do a couple of measurements last week with the six different loaves I was making.
My 100% semolina durum started off at 5.0 at the start of BF, but my 60% rye at 4.6, which really worried me. I checked the pH again when I gauged a 50% rise, which is normally when I end BF for dark loaves, and the rye was down to 4.0. It probably went into the oven a little lower at 3.8 (same day bake), and thankfully the rise was still excellent. I did allow the semolina to continue with BF until 4.3 (about 75% rise) before shaping it.
I'm baking a couple of loaves again on Thursday and would be happy to share more measurements.
I think that the pH measurements are generally useful for me to gauge BF cutoff to prevent soup situations with very brown loaves.
I think I'm going to keep checking the pH even if I don't really know what I'm going to do with the data, and I'll see where it takes me...In the meantime, here is my 50/50 semolina Rimacinata/Bread flour bread: pH 5.8 after kneading, 4.25 at the end of the bench rest, before going into the fridge (I forgot to check the pH before baking); I think I could have pushed it a bit further!
Great looking loaves with good open crumb for 50% sem. rim!
If you forget to check pH before baking (I often do as well!), then just check the bread crumb pH once baked.
Just take 3g bread crumb without crust mushed up in 20g preferably deionised water in pestle and mortar if you have one or just use a wooden spoon and take the pH.
I prefer doing this as you are not poking holes in your shaped dough. I found that crumb pH was very similar to final dough pH and also it is stable for at least a day - ie it doesn't keep dropping.
Lance