Question regarding ppms of Starsan acid

So 1oz of Starsan in 5gallons of water is supposed to provide 300ppm of dodecylbenzenesulfonic acid and 780ppm of phosphoric acid. To sanitize at this solution, it is recommended that the solution makes contact with the surface for 30seconds.

Does any chemist on here know if I can use lower concentrations for longer time? Like 150ppm dodecylbenzenesulfonic acid & 390ppm phosphoric acid for, say, 5 minutes?

It would be a great way to save sanitizer but I'm sure there's some sort of threshold below which it would no longer be acidic enough to kill bacteria.

Very good question. I am not a microbiologist, but I await an answer. At a lower concentration, I'm not sure if it will work like heat deactivation does where say 1 minute at boiling kills 100% and 15 minutes at 150F kills 100%. There is probably a minimum concentration at which the organisms we are trying to kill just thumb their 'noses' at us and laugh.

I'm guessing the answer is "no", because reliably killing bad bugs takes a certain pH. You could always email the company and find out, though!

From what I understand, Star San loses effectiveness above a PH of 3.5. Maybe you could mix up a batch using the dilution ratio you're questioning and test the PH?

The dodecylbenzene sulfonic acid is just a surfactant. It is the phosphoric acid which is doing the job and its effectiveness depends on the pH it is able to establish. The recommended dose would result in a pH of about 2.33. Halving the recommended dose would result in a pH of 2.56 i.e about 0.23 pH higher. This doesn't seem like much and only amounts to a decrease in hydrogen ion activity of 40%. All this assumes distilled water. If water of alkalinity 80 (more or less typical) were used the recommended dose would give a pH of 2.44 and the product must be designed to work with water at that level of alkalinity. So I'm guessing that it would work at half strength if mixed with DI or RO water.

Note that articles on acid washing of yeast seem to indicate that the pH should be 2.2. I found one pro brewer who advances the rule of thumb: pH 2.2 - 2hrs; pH 2.4 - 4hrs; pH 2.6 - Overnight.

To say that the dodecylbenzene sulfonic acid is "just" a surfactant is a bit of an understatement. As it is registered as a sanitizer as a stand-alone product the concentration obviously important. To the OP, I would not be able to say if it was effective at lower concentrations, but I would just remind you that this product is reusable so you should not be needing to use that much of it. Many homebrewers find that their solutions are pH stable for months and so they can keep re-using it.

If Star-san was only a pH adjuster then it would be much cheaper to just buy some phosphoric acid.

theredben said:

To say that the dodecylbenzene sulfonic acid is "just" a surfactant is a bit of an understatement.

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Yes, I guess it is. Saying "just" a surfactant implies that it does not have a role in the sanitization process which it does. But for it to work properly pH must be set to between 2 and 3 and that's the job of the phosphoric. The ddbsa is an anionic surfactant and it is the attraction of the anion to the surface of positively charged bacteria that make it effective but at pH 2.5 only half of it is ionized. At pH 3.5 more would be ionized but the mix is then no longer effective so it is clear that the low pH established by the phosphoric acid plays a major role here. I guess it takes care of the gram negative bacteria which are negatively charged.

As the ddbsa has a molecular wt. triple that of phosphoric acid and a pK of 2.55 as compared to phosphoric's first pK of 2.15 it will be the phosphoric that has the major effect on solution pH so the calculations in the previous post are probably valid and OP should be OK as long as his dilution does not raise pH > 3. Should he increase contact time for the same log kill? I'm guessing if he diluted by a factor of 2 he should double contact time i.e. maintain same CxT. But I agree that the manufacturer should be consulted.

theredben said:

If Star-san was only a pH adjuster then it would be much cheaper to just buy some phosphoric acid.

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And that's exactly what I do.

I think you should use the recommended dosage to achieve the best results. On the other hand, why not use 2.5 gallons of water and .5 oz. of Starsan for a 5 gallon carboy. I would rather use less solution than use the wrong dose.

I wouldn't think contact time would make a difference at a lower concentration since the process isn't a chemical reaction.

The effectiveness of sanitizers is frequently expressed in terms of CxT for a specified log kill ratio. Thus, for example, EPA requires 1850 min-mg/L chloramine against giardia at 10 °C for a 3 log kill (99.9%) whereas 23 min-mg/L is sufficient for chlorine dioxide and 1.4 for ozone. This means that if you have a chlorine dioxide concentration of 2.8 mg/L a half a minutes exposure will take care of giardia but if you halve the concentration to 1.4 you must expose for a minute. For 4 log inactivation of viruses the numbers for those 3 disinfectants are, respectively 1491, 35.1 and 1.

With an anionic surfactant/acid sanitizer there is a limit once the pH rises appreciably above 3, but I don't see any reason why the same principle (Chick's law) shouldn't apply to this type of sanitizer but this is hardly my area of expertise.

The process isn't a chemical reaction? Sounds like one to me but wonder what sort of mechanism, other than chemical you have in mind.

I'm no chemist, but I can tell you that using Starsan is VERY cost effective. The reason is that a slightly stronger solution of it will kill just as well, and will keep for a very long time, and reused over and over (as long as the pH is kept below the required level.)

I normally mix 1/4 ounce in 3 quarts of distilled water. That's stronger than required for a gallon! But for me it's just easier to measure. I keep this in a 3-quart jug (the reason I am mixing 3 quarts is because I like these jugs) and use it to top off a spray bottle.

I normally use a spray bottle to apply it. Sometimes I will pour some into a carboy or bucket and use a cloth to wipe it around and then pour the excess back into the jug.

1/4 ounce of Star San will last me a couple of MONTHS.

I highly recommend using distilled water since alkaline water can neutralize the Starsan solution after a short time.

Homercidal said:

I highly recommend using distilled water since alkaline water can neutralize the Starsan solution after a short time.

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I agree that mixing with distilled water is the ideal route, RO is nearly as good. In addition, I've found that ion-exchange softened water is also a decent water to use. While it could still have a dose of alkalinity, apparently the real mechanism of StarSan degradation is excessive hardness. The extra alkalinity just means that you might have to add a little extra StarSan to the water. IMHO, this is the only use for ion-exchange softened water in brewing.

as far as I can tell the mechanism is a physical process. The negatively charged surfactant binds to the cell walls of the bacteria, which destroys the cell.
The phosphoric acid is there to simply keep the pH correct.

Homercidal said:

I highly recommend using distilled water since alkaline water can neutralize the Starsan solution after a short time.

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How short a time if using tap water with an alkalinity (CaCO3) of 90? A day, a week, a month?

IDK. I made some up and when I went to use it later it was cloudy and I was all like WTF??

Then I read the FAQs and they said if you have hard water to mix with distilled. I've done it ever since. Back then I didn't have a good way to measure pH.

I think 2.5 gallons of distilled water is like $2.50 here at the store. I buy 5 gallons of it for $4 at work and what I don't use brewing I use for starsan.

josephus23 said:

as far as I can tell the mechanism is a physical process.
The phosphoric acid is there to simply keep the pH correct.

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We are obviously quibbling about definitions here but all chemistry is ultimately physics. The pH goes to the value it does given the species present because at that pH the Gibbs energy is minimized. An enzyme works by holding a substrate molecule in such an orientation that a site on that molecule is exposed to attack by another reactant molecule thus increasing the probability that the attack will be successful and so on. These are obviously physical things, and the mechanics are studied by people called physical chemists, but they are chemists nonetheless.

josephus23 said:

The negatively charged surfactant binds to the cell walls of the bacteria, which destroys the cell.

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But how? That's not a full explanation. The surfactant does something to the bacterium like interfere with an enzyme that mediates transport of something in or out of the cell. I'm not saying that is what happens - I don't know- but it is probably something like that.

More to the point: whatever the mechanism or what it is called, the rate of kill is proportional to the number available to be killed thus the log of the population decreases linearly with time. Thus Chick's law is likely to be applicable.

jmf143 said:

How short a time if using tap water with an alkalinity (CaCO3) of 90? A day, a week, a month?

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Immediately. H3PO4 + HCO3- ---> CO2 + H2O + H2PO4-

But even 90 ppm alkalinity shouldn't pull the pH much higher than 2.44 which is still less than 3. The turbidity is puzzling though. At pH < 3 the amount of phosphate is small (tiny) enough that the solution shouldn't be saturated WRT calcium phosphate at the level of calcium which would be necessary to offset 90 ppm of alkalinity. DDBSA is a detergent (classed as a soap). Perhaps the haze is the calcium salt of DDBSA i.e. soap curds typical of hard water.

My guess is that the Dodecylbenzenesulfonic Acid surfactant disrupts the cell membrane. Since the cell membrane regulates the membrane transport of nutrient and osmotic pressure. This process causes the inactivation of cytochromes and ATP synthase. Without ATP the cell can't regenerate.

I wonder if you can use Star San and a lower concentration and just add some acid until the pH is in the correct range. Then use a longer contact time.

I think that's a good guess. The membrane is made up of lipids and DDBSA is a detergent.

Summarized from what Charles Talley of 5 Star said:
wetting agent (foam) that softens the cell wall of bacteria and the sugar coating. Once soft the phosphoric acid will rupture the wall kill both parent and baby.

At this point the picture that is forming in my mind is that the DDBSA is just a surfactant (sound familliar) but that it plays a very important role in allowing the phosphoric acid to do its job. The hydrophobic end (alkyl part) dissolves in cell wall/membrane sugar/lipid while the charged part (hydrophylic end) is attracted to water molecules in classic soap/detergent fashion so that it can "wash"away some of the wall/membrane. IOW the efficacy doesn't come from the anionic end being attracted to positively charged bacteria (that just bothered me) but that it is attracted to the rump end of water molecules, again as with any soap or detergent.

Given compromise in the cell membrane and/or wall the protons from the phosphoric acid now have improved access to the interior of the cell where they can establish a pH low enough to denature many of the enzymes that mediate the cell's biochemistry thus rendering the cell incapable of metabolizing nutrients, reproducing....

I'm starting to feel bad for the poor little bacteria...

MNDan said:

I'm starting to feel bad for the poor little bacteria...

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Do you know what it means to be emulsified?

I know I'm resurrecting an old thread, sorry. If I have very alkaline water (172 CaCO3 ppm per Ward Labs), how much do I need to increase the concentration of starsan in my solution?

The simple answer is if you mix up your StarSan and it's still cloudy, add more until it isn't cloudy since StarSan is designed to cloud when the pH gets too high.

MNDan said:

..since StarSan is designed to cloud when the pH gets too high.

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If that's the case (and I don't doubt that it is) you might want to just add a bit of cheap hydrochloric or phosphoric acid until it clears. If your alkalinity is 172 ppm as CaCO3 you will need 172/50 = 3.44 mEq/L. That's 3.4 mL of N hydrochloric acid per liter (the hardware store stuff is about 12.39 N).

BrewThruYou said:

I know I'm resurrecting an old thread, sorry. If I have very alkaline water (172 CaCO3 ppm per Ward Labs), how much do I need to increase the concentration of starsan in my solution?

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My understanding is that at concentrations much beyond the manufacturers' recommendations, StarSan is no longer a "no rinse" sanitizer, i.e., if you dump a bunch of this stuff into your water to overcome the alkalinity, you may start impacting the flavor of your beer.

I don't have a cite for this but I'm sure I remember a discussion of it.

That's really the idea behind using just the acid necessary for pH correction. A bit of additional phosphoric acid on the vessel walls won't hurt anything or effect the flavor of beer subsequently put into it. Additional detergent (DDBSA) very well might.

Thanks for helping me out. I think I'm either going to add some phosphoric added to the starsan solution or just switch to iodophor. AJ, is there a calculator somewhere that can help me figure out how much 10% phosphoric to add? I'll take pH readings, but I'm just wondering if there's something that will tell me how much acid to add to bring down the pH to a proper level.

MNDan said:

I'm starting to feel bad for the poor little bacteria...

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I hear the tree hugger crowd is pushing for a live trap.

Filter out the bacteria and set it free. :cross:

BrewThruYou said:

T AJ, is there a calculator somewhere that can help me figure out how much 10% phosphoric to add? I'll take pH readings, but I'm just wondering if there's something that will tell me how much acid to add to bring down the pH to a proper level.

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It should be something like 3.7 mL of 10% phosphoric acid per liter of water treated to take the pH to 3.5 depending slightly on the pH of the starting water. It is definitely a good idea to check the pH and strips are probably OK here because the usual brewing application problem of staining by wort does not apply.