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Author Topic: Amount of alcohol needed to preserve a liquid/syrup?  (Read 314 times)

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thesun

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Amount of alcohol needed to preserve a liquid/syrup?
« on: January 05, 2017, 07:37:40 AM »

I am totally NOT a chemist, but am hoping someone here who IS can help me with a bio-chemical question.  I make a lot of syrups and such for home bartending, often it takes months or even longer to use them up.  The kind of thing where it's easy to make a liter or 8oz batch but I only use a tablespoon at a time. 

I've posted on some bartending forums but people just give answers like, "It should last a few months" and I'd like to get a really solid answer:  What should the ratio be to make sure I've got a truly shelf-stable product?  In the case of grenadine, it's a 1:1 ratio of pomegranate juice and sugar.  I know the sugar will retard spoilage for a while, but I'd like to add a minimum amount of alcohol, since grenadine is used in non-alcoholic beverages too.  If I have 8oz of grenadine...1oz of added 95%ABV (Everclear)?  2oz?

Thanks so much if there's anyone out here who knows for sure what the answer is.  Or how I can do some pretty good calculations...if it's a liquid with far less sugar, I'm sure more alcohol is needed.  Would love to know what those metrics are. 
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Arkcon

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #1 on: January 05, 2017, 11:42:14 PM »

Briefly, we don't give specific advice on this forum on how to make something someone will eat.  This is a liability issue, and I'm going to use the rest of this post to help you understand why.

You're asking for the specific metrics, with ratios of sugar to alcohol.  Such things don't exist.  Traditionally, high sugar, and high alcohol solutions remain germ-free for indefinite periods of time.  I said "indefinite" because that means months, not years, but we're not sure, so don't make too big a batch, and rotate stocks...  And I say recipes because no one really tries to be scientific about it -- if it spoils, they throw it away, instead of trying to determine the least that will work for what period of time.

I can point you to some peer-rewied information.  It has been experimentally determined that the salmonella producing bacteria in eggs can be killed, over a period of months, in a 30% ethanol solution.  Which can then be diluted with cream to make egg nog.  But you said you don't want it to be that strong an alcohol solution.

https://www.cooksillustrated.com/features/8318-how-we-developed-great-and-safe-aged-eggnog
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thesun

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #2 on: January 06, 2017, 04:25:06 AM »

Hi, thanks for the info and very sorry to post something that's not allowed.  I looked on the forum rules prior to posting and it wasn't explosive or drug-related, (well, I guess technically alcohol's a drug but this is for a NON-alcoholic product).

Actually, I've been using the Cook's Illustrated method for eggnog for several years, that exact recipe, and that's what prompted me to try to find out the answer to this question.  I'm fine with 30% if that's what it takes, but the "citizen scientist" in me is just curious about where and when that line gets drawn.  Especially since sugar itself is a preservative, whereas eggs are a host and possibly already contaminated.

Perhaps someone can just answer the math question side:  For an 8oz quantity of non-alcohol liquid (i.e. syrup), what quantity of 95% pure alcohol would I need to add to get the liquid to a 30% ABV?

Anyway, again, sorry to post a non-allowed question.  I'm a bit disappointed though, as this seems like just the kind of interesting info the web and its hive-mind are able to provide and I feel like the legal risk is pretty minimal.  Perhaps if anyone out there wants to answer it directly they could PM me and we can discuss it out of the public eye?  I can PM my email or something so it's not even discussed directly on the forum at all.

Again, thank you for taking the time to explain and I'll keep fingers crossed that someone out there can add some useful info without opening up the site for a lawsuit.

 
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AWK

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #3 on: January 06, 2017, 04:49:01 AM »

I remember, when I was a teenager, I helped my mother in preparation red- and blackcurrent jelly.
Juice, fresh pressed from berries, was mixed with sugar (1L to 1.5 kg) to complete dissolution (~2 hrs), then put into jars, covered with disks of cellophane, then with a few drops of 95 % alcohol, twisted on and  to the cellar. At least nothing bad happened for a few years.
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thesun

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #4 on: January 06, 2017, 08:48:25 AM »

Was the alcohol just floated on top?  Or mixed in?  And how much is "a few drops"?  That's been part of my problem...there are lots of recipes but hard to find specific measures.  :-)  But thank you for taking the time!
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AWK

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #5 on: January 06, 2017, 09:09:02 AM »

Just a few drops on the cellophane disk (1-2 ml), and immediately closing on the jar.
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Intanjir

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #6 on: January 06, 2017, 09:22:35 AM »

I'm not sure if adding only a small amount of alcohol would help all that much.
The water activity of a syrup is low and bacteria already won't grow well.
It has been my experience that you get some kind of mold on the surface of jellies and syrups and that is what prompts me to discard them.
Molds are fungi and so relatively resistant to ethanol just like your cells or those of other eukaryotes.
Ethanol should still help though, but my intuition is that you would need more than a small amount.

Strains of brewer's yeast can tolerate alcohol up to 15-25% depending on the strain.
Obviously this number will lower if the water activity is also very low because of the sugar content.
So, 30% seems like a more than safe number.


As for the math, you want 30% of the total volume of mixture to equal the amount of alcohol in the Everclear(which is 95%).
0.3*(Syrup+Everclear) = 0.95(Everclear)

So solve for Everclear! (Algebra and alcohol: solve for your solvents)  ;D
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thesun

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #7 on: January 10, 2017, 08:41:58 AM »

Thanks so much for the help.  I really appreciate this.

My algebra is literally coming from high school, but does this properly solve for "e"?

.3*(s+e) = .95e

.3s + .3e = .95e

.3s = .65e

e = .3s/.65

Therefore, to make 8oz of syrup 30 percent alcohol, I'd add 3.7oz of Everclear.

(.3x8)/.65 = 3.69
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Intanjir

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Re: Amount of alcohol needed to preserve a liquid/syrup?
« Reply #8 on: January 10, 2017, 10:11:10 AM »

yup!

To check just plug 3.7 and 8 back in to the original equation and verify that both sides come out the same (they do).
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