June 16, 2020 - 6:47pm
CO2 Disappearing act
Vacuum sealed for 2 months at ~8C. What was once tightly bound and rock solid due to the intense gas pressure has now finally dissipated.
I presume all or most of the CO2 got converted into carbonic acid.
As shown below it is the dominant chemical species at low pH.
This got me thinking... Carbon capture (fixation). Turned up this:Carbonic-Acid-Fix-Carbon.html
On a more trivial note the aroma of this dough was like a nice glass of Chardonnay, sur lie style.
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If left to warm up will it expand?
While gasses dissolve more readily at lower temps they're still gasses CO2 (aq). The tendency for it to become carbonic acid is dependent on further factors and concentration probably plays a role.
The package remained under high pressure for about 6 weeks before it showed signs of softening. It continued to get softer in those last few weeks.
It didn't expand at room temp, I can assure you the gas has gone. The dough tasted very acid but in a pleasant way, not at all acetic but certainly carbonic acid like.
I've seen this effect before but this time I have ruled out gas leakage with the vacuum seal.
While the vacuum seal is pretty good, it is not hermetic, and if there is a pressure gradient across the container there will be slow leakage of gas in proportion to the partial pressure difference. On the inside the partial pressure of CO2 is a little above atmospheric pressure (assume 800 mm of Hg) and on the outside the partial pressure of CO2 is normal sea level value (about 0.3mm of Hg). The leakage rate also depends on the permeability of the wrapper material and both polyethylene and especially nylon have high CO2 permeability). PVDF also leaks CO2 at fairly high rates which allows a bowl covered with PVDF to retain water and allow CO2 to escape.
Partial pressure is proportional of the total pressure of a system. The vacuum sealed dough package was bound (constricted volume) and under pressure. I estimate approx. ~4-5 bar, so the partial pressure of CO2 would be far greater than 800mm Hg in my case.
It appears that a doubling of pressure (atm) roughly doubles the solubility of CO2.
Compressibility, fugacity, and water-solubility of carbon dioxide in the region 0-36 atm. and 0-100°C
Michael, in the image above, why didn’t the dough expand to fill the bag? On close inspection it looks like the dough may have been bound, not from the vacuum bag but around the dough. Is that the case?
I am familiar with acetic and lactic, but what is carbonic acid and how does it affect flavor?
Lastly. I’d imagine that you are familiar with Doc’s theory (2% weight lose of the total weight of the flour) pertaining to calculated weight lose indicating the maturity of a starter. Could this be part of the explanation?
A lot of questions, I know. I am inquisitive even when not knowledgeable.
Danny
”inquiring minds want to know...”
Hi Danny,
That's right it was bound and the expansion you can see it the result of untying the package. It had fermented for about 24 hours or so.
I would describe Carbonic acid as "zingy" / tart. Sparkling water is often described as having a sour taste because of the presence of carbonic acid. CO2 can be used as an atmosphere to preserve some foods and because of this I can recall tasting the carbonic acid in a cut and prepared fruit salad.
I am aware of Doc's 2% weight loss specification but I cant say I understand it. Perhaps you can ask him to chime in...
Michael
Michael,
See this string from 2017:
http://www.thefreshloaf.com/node/51875/judging-levain-maturity-weight-loss
I think there are some other posts that contain plots of weight loss vs time for various temperature and time combinations. The plot below was for a month in the refrigerator which I took as good evidence that a starter will last that long without being fed. Also shows that there is plenty of sugar left in the starter after 2% of the added flour weight has been burned up by the LAB + yeast metabolism to keep it alive and active for quite a while.
Long Term Starter Storage Weight Loss.jpg
This data was collected on a digital scale with a resolution of 1 mg and an accuracy of ~5mg with a total weight (container, lid, flour, starter, water) of around 40g. So the added flour weight was 15g and 2% was 300mg. The three starters have similar but different origins and continue to express different growth profiles over repeated refresh cycles.
Michael, do you think there might have been some CO2 loss through the plastic of the bag? I guess you could check by periodically weighing the sealed bag with 0.1g accurate scales.
Lance
Certainly it would have been useful to track the weight but if some gas did pass through the plastic it is likely to be very negligible in relative terms.
Although it was an eye-opener to learn wine closures at college and how air can pass through a surprisingly wide range of materials. IIRC air passes about 10 times faster through a synthetic cork compared to a traditional cork.
Michael
Doc. Dough's reply above regarding permeability of PE was valuable. It would be fair to say I overlooked the ability of this material to hold gas and specifically CO2.
I think making use of an empty carbonated water bottle made with PET would be more conclusive to determine the level of fixation of CO2. Although that was never my intent. Merely an observation of happenstance.
Could carbon fixation and wastewater treatment be incorporated? Bacteria are used to decompose BOD anyway... Just a thought, I am likely wrong for I have very limited background in the field.
On another note, I wonder if this is how we produce intensely sour yeasted dough. A small percentage of the compressed dough may at added to the main dough as a flavor enhancer. This might be for those who are not yet ready to maintain a SD starter, or find acetic acid too assertive.
Indeed I am wondering if there is a further application here.
Not sure about that as method for yeasted doughs. If you boil sparkling water does the sour taste remain?
I had completely forgotten about the concept. How could I...
In this sense, would the released CO2 contributes towards thermal expansion of dough?
Perhaps I misunderstood your question. In fact dissolved CO2 coming out of solution as bread bakes does contribute to dough expansion under some circumstances. You can see it most dramatically when you retard dough and then bake it with lots of steam. It that case you can get tons of quite large blisters errupting on the surface of the dough. I believe the phenomenology goes something like this. As the dough chills the solubility of CO2 goes up but the yeast continues to produce CO2 while the dough remains saturated so there is a balance between volume expansion, leakage, and absorption of the CO2. Deep in the dough leakage is not really taking place except the migration of CO2 between alveoli as they change shape and create minor pressure differences between them. But the dough can hold a lot of additional dissolved CO2 (think about how many bubbles you get when you open a bottle of seltzer or sparkling water, and how much additional gas is given off from a glass of champagne as it warms up from near freezing to room temperature). When the dough sees a hot oven and condensing steam cooks the starch, it forms a gas tight membrane. After that as the dough warms up, the dissolved CO2 has to come out of solution and shows up as a trapped bubble under the cooked surface starch forming a blister. The same thing is going on deeper in the dough as well, except that you can't see it. There, the evolved gas just adds to the CO2 already trapped in the alveoli and expands along with the rest of the trapped gas as the dough temperature rises. It that case it does contribute to thermal expansion of the dough.
I am aware of the dough expansion effect resulted from CO2 dissolved at low temperature. This makes me wonder if the pressurized dough could be used to incorporate more CO2 (in the form of carbonic acid) into the main dough. Under general condition, only a certain amount of CO2 can be trapped in the alveoli. In my understanding, this is limited by the pressure that air cell walls can withstand.
At around 60°C, starch gelatinization starts to take place. Starch granules in the gluten matrix swell and may deform into elongated form. Air cell walls are strengthened, which allows the cells to expand further. Since cell walls can now tolerate greater pressure before rupture, the alveoli could reach larger size as compared to before (when the dough has not hit the oven). So my thinking is, perhaps the additional dissolved CO2 would help increase bread volume. Or maybe the dissolved CO2 level would have leveled off as it reaches the critical pH, so it would not serve this purpose.
Please do point out any misconceptions I might have. As you can probably tell, I haven't taken proper fundamental physics or chemistry classes :)
CO2 solubility is very low in water at elevated temperatures.