Iodine tests

[oldschool]

Can someone explain the iodine testing to me? I know that you are testing for the presence of starches. Is this telling you the same thing as a refractometer only with fermentables? How accurate is the iodine test compared to the refractometer-and do many brewers use that kind of tool. I've mostly heard of wine makers using them to measure the sugar content of grapes. thanks, school

 

[Reno_eNVy]

The iodine tells you absolutely nothing about the amount of fermentable sugars in the solution. The only thing it does is indicate if there are still non-converted starches left. No color change = conversion is complete, no starches. Purple/Black color change = starches remain.

 

[shortyjacobs]

So I just asked about this recently, and according to Yuri and Kaiser, iodine measures how much starch has been converted to sugar. Like Reno said, no color change, everything is sugar...black result means starches still remain.

That said, just because you converted all the starch to sugar doesn't mean you converted it to FERMENTABLE sugar. Just sugar in general. Here's Kaiser's post on that, (very helpful)

technically, the iodine reaction stops once an unbranched chain is shorter than 9 glucose units. It can be longer for branched chains. http://braukaiser.com/wiki/index.php?title=Carbohydrates#Reaction_with_iodine

But there will be fermentable sugars in the wort. I suggest you do a fast ferment test to derdermine the fermentability of the wort as it will be higher than what you would normally expect.http://braukaiser.com/wiki/index.php?title=Fast_Ferment_Test

 

[oldschool]

Okay, so you just take a sample of wort(however much?) and mix it with an undefined ammount of iodine? like medical grade iodine? what about the ratios?

 

[Yuri_Rage]

No real ratio required. It's a very simple test. Put some wort on a white saucer. Put a few drops of iodine into it (no need to mix/stir). If the iodine drops turn purple/black, starch is present. If the iodine remains brown-ish, no starch is present.

This link describes both the saucer method and an alternate method using a big piece of chalk:

https://www.homebrewtalk.com/wiki/index.php/Iodine_test

 

[oldschool]

No real ratio required. It's a very simple test. Put some wort on a white saucer. Put a few drops of iodine into it (no need to mix/stir). If the iodine drops turn purple/black, starch is present. If the iodine remains brown-ish, no starch is present.

This link describes both the saucer method and an alternate method using a big piece of chalk:

https://www.homebrewtalk.com/wiki/index.php/Iodine_test

Would you think that a refractometer would be a better method? Although they can be quite pricey..

 

[The Pol]

Would you think that a refractometer would be a better method? Although they can be quite pricey..

A refractometer ($30) is just a fancy hydrometer, it will NOT measure conversion.

Iodine tells you if you have converted your starches. A refractometer tells you the concentration of sugars, two completely different things. I have a refractometer, and I am starting to use iodone to test for conversion.

 

[oldschool]

A refractometer ($30) is just a fancy hydrometer, it will NOT measure conversion.

Iodine tells you if you have converted your starches. A refractometer tells you the concentration of sugars, two completely different things. I have a refractometer, and I am starting to use iodone to test for conversion.

I disagree, a hydrometer tells you something way different. You can up your gravity on the hydrometer by adding sodium chloride, sodium bicarbonate, or anything soluble for that matter(not just sugar). You are saying that the iodine test will tell you if you have starches present, not sugar. And a refractometer tells you how much sugar is present, not starch. Is this not acheiving the same goal, only iodine test will not reveal a precise quantity of starch.

 

[The Pol]

I disagree, a hydrometer tells you something way different. You can up your gravity on the hydrometer by adding sodium chloride, sodium bicarbonate, or anything soluble for that matter(not just sugar). You are saying that the iodine test will tell you if you have starches present, not sugar. And a refractometer tells you how much sugar is present, not starch. Is this not acheiving the same goal, only iodine test will not reveal a precise quantity of starch.

Wow,

Yes a hydrometer will give you the density of a fluid, but if we are talking about brewing beer here, which we are, hydromters tell you exactly what the hydrometer does, the SG of the wort. I dont care about everything else because it does not apply to brewing.

A hydromter tells you how much sugar is present, just like a hydrometer. They accomplish the exact same goal. Iodine will not tell you precisely how much starch you have, nor will a hydrometer, refractometer. A refractometer will not indicate the presence of starches any better than a hydrometer, which is not at all....

For instance, I can measure the wort and get 10 Brix in the refractometer, so how much starch is left? Is there any? Tell me.

Also, I can measure a wort that is 10 Brix and it is not completely converted, I can measure another wort that is 10 Brix that is 100% converted... still not indicating whether or not conversion is complete.

To determine if conversion is complete, you need to measure starch, refractometers do not measure starch, but iodine will indicate its presence.

Or you can use Kai's spreadsheet that indicates conversion based on the SG of the wort and the water to grain ratio used. But again, that is based on SG, which refractometers and hydrometers are both used for.

 

[Yuri_Rage]

Actually, a refractometer reading will be affected by other dissolved solids, also. In fact, you can buy a refractometer designed to measure starch concentration. Also, even if starch had a minimal impact on a refractometer reading, using a refractometer to test for conversion would require you to know the mash efficiency with a rather exact amount of precision. Simply put: a refractometer is ill-suited for testing mash conversion.

 

[The Pol]

Can someone explain the iodine testing to me? I know that you are testing for the presence of starches. Is this telling you the same thing as a refractometer only with fermentables? How accurate is the iodine test compared to the refractometer-and do many brewers use that kind of tool. I've mostly heard of wine makers using them to measure the sugar content of grapes. thanks, school

Refractometers are used to measure SG, just like a hydrometer. Measuring starches (dont know that anyone measures them) would be completely separate, comparing iodine to a refractomter isnt even comparable. Iodone tests for the presence of starches, that is all. If any are present, then conversion is not complete.

 

[The Pol]

Actually, a refractometer reading will be affected by other dissolved solids, also. In fact, you can buy a refractometer designed to measure starch concentration. Also, even if starch had a minimal impact on a refractometer reading, using a refractometer to test for conversion would require you to know the mash efficiency with a rather exact amount of precision. Simply put: a refractometer is ill-suited for testing mash conversion.

Exactly, which is why when you buy a refract, you have to find the Brix correction factor. Mine is like 1.054. This takes into account other solids in the wort. There are plenty of things that WILL affect hydrometers and refractometers, but we use them to measure the same thing, sugars. I dont use my refractomter to determine how much "other stuff" is in there

 

[oldschool]

Wow,


A hydromter tells you how much sugar is present, just like a hydrometer. They accomplish the exact same goal. Iodine will not tell you precisely how much starch you have, nor will a hydrometer, refractometer. A refractometer will not indicate the presence of starches any better than a hydrometer, which is not at all....

For instance, I can measure the wort and get 10 Brix in the refractometer, so how much starch is left? Is there any? Tell me.

Also, I can measure a wort that is 10 Brix and it is not completely converted, I can measure another wort that is 10 Brix that is 100% converted... still not indicating whether or not conversion is complete.

To determine if conversion is complete, you need to measure starch, refractometers do not measure starch, but iodine will indicate its presence.

Or you can use Kai's spreadsheet that indicates conversion based on the SG of the wort and the water to grain ratio used. But again, that is based on SG, which refractometers and hydrometers are both used for.

I know that we are not on the topic of hydrometers but a hydrometer will not just tell you how much sugar is present. It will also be effected by the ammount of starch in solution since it is one of many unfermentable carbs that are soluble in water. Back to what i disagreed upon, a refractometer is not at all "just a fancy hydrometer."

 

[oldschool]

Refractometers are used to measure SG, just like a hydrometer.

Incorrect. As yuri said a refract. measures sugar(and now i know, certain ones measure starch) concentrations of a solution, not the specific gravity.

 

[The Pol]

I know that we are not on the topic of hydrometers but a hydrometer will not just tell you how much sugar is present. It will also be effected by the ammount of starch in solution since it is one of many unfermentable carbs that are soluble in water. Back to what i disagreed upon, a refractometer is not at all "just a fancy hydrometer."

For our purposes, it is. What more does it tell you, I need to know, other than the SG? I have both, and damned if they dont tell me the exact same thing when I am brewing. One tells me that the SG is 1.040, and the other tells me that the SG is 1.040... I dont see a difference. The funny thing is that they tell me the exact same thing, and nothing more or less. Though I do prefer the refractomter because the sample size is tiny and can be taken hot.

 

[oldschool]

SG is ALL that a hydro will tell you. has nothing to do with a refractometer.

 

[Yuri_Rage]

Still not quite correct. A refractometer tells you the index of refraction of a solution. When using a Brix refractometer, one assumes that the only dissolved solid in otherwise pure water is sugar (thus the correction factor mentioned by The Pol). Other dissolved solids will impact the refractive properties of the solution. Therefore, you cannot use a refractometer to distinguish starch from sugar (at least not with the equipment usually involved in homebrewing beer).

Thus, an iodine test coupled with a specific gravity measurement (however you get it) will net the results you seek.

 

[The Pol]

Refractometers are used to measure SG, just like a hydrometer.




Incorrect. As yuri said a refract. measures sugar(and now i know, certain ones measure starch) concentrations of a solution, not the specific gravity.

For our purposes they are the same. My refract tells me my SG, so does my hydrometer.

You should use your quote thingy to show where I said "for our purposes". Just sayin...

All a refract tells you is Brix, which after using a correction factor gives you Plato and SG. All indicating the concentration of sugars in your solution. We as brewers use them to tell us the same thing, and one thing, the SG of our wort. Still, having nothing to do with starches in the mash being present. They measure sugar in completely different ways, but they provide the brewer with the exact same information in the end. Like I said, I just prefer the refract for the small sample and no need to cool the sample.

 

[The Pol]

Incorrect. As yuri said a refract. measures sugar(and now i know, certain ones measure starch) concentrations of a solution, not the specific gravity.

Yes, the refrcacts that we brewers use measure sugar, some measure engine coolant... but, ours measure sugars, and that measure of sugar IS defined as the SG of the solution.

Like Yuri said, outside forces affect both tools, but the refract is corrected for them with the Brix correction factor.

This being said, you can use a starch refract to measure the amount of starch in the solution, I think that most brewers have bypassed this because the iodone test is so much less costly and probably just as reliable.

 

[oldschool]

Yes, the refrcacts that we brewers use measure sugar, some measure engine coolant... QUOTE]

Are you sure that some refractometers are used to measure engine coolant?

 

[oldschool]

regardless, my iodine question was answered. I also got some inspiration to research the theory and function of a refractometer. I'm getting a rundown at a local brewery by one of their brewers tomorrow morning. I will have to ask them how they do it. thanks

 

[The Pol]

Yes, the refrcacts that we brewers use measure sugar, some measure engine coolant... QUOTE]

Are you sure that some refractometers are used to measure engine coolant?

Yep, pretty sure.

http://www.tequipment.net/ExtechRF40.asp

 

[Kaiser]

A refractometer made for testing starch concentration will not be able to tell you the starch concentration in wort. This is because like the Brix and engine coolant refractos it only measures refractive index and its scale is calibrated assuming pure starch, pure sugar or pure engine coolant solutions.

I’m inclined to say that if your gravity reading (corrected refracto reading or hydrometer) is close or at the max that you can determine from mash thickness and grain extract potential, your iodine test is very likely to me negative. This is because your mash went well enough to dissolve all or nearly all of the starches in the grain and should have yielded full conversion.

If you do the iodine test, give the test on chalk a try. It is so much easier to read and you can even tell color nuances. Preparing a series of iodine tests during the mash (every 10 min for example) is a great way to learn how conversion progresses and how the iodine reaction changes. This is not something you would so everytime, but many here are geeky about brewing and would like to see that. It won’t make your beer better, but you may gain more confidence in what you are doing.

In (large) commercial brewing, an iodine test may even be done photometrically where a photometer is used to detest a starch (actually it’s mostly large dextrins) and iodine reaction.

Kai

 

[shortyjacobs]

It's very simple:

A hydrometer measures specific gravity of a liquid. NOT sugars. NOT starches. NOT dissolved baking soda. As brewers, we assume that the only thing affecting SG is sugar, because that's the only assumption we CAN make. We MAKE this assumption after doing an iodine test to prove we have no starches left. If we assume there are both starches AND sugars, then we have no way of telling how much of each we have, since we have two unknowns and only one data point.

A refractometer measures refractive index. NOT sugars. NOT starches. NOT anything else. We ASSUME the only thing affecting refractive index is sugar concentration, for all the reasons listed above.

Yes, refractometers are used to test engine coolants, or battery levels, or ANYTHING where a solute or diluent could affect the RI. Along the same line, hydrometers are used to test battery levels, engine coolants, or anything where a solute or diluent could affect SG.

Arguing if a refractometer OR hydrometer can test for anything other than RI or SG, (respectively), is patently wrong. You can argue all you want about what ASSUMPTIONS we make to convert SG or RI readings into numbers we can use, (like amounts of sugar, etc.), but in the end, those devices are only telling you SG or RI, which is RELATED, but NOT INDICATIVE, to/of brewing related worries.

 

[oldschool]

It's very simple:

A hydrometer measures specific gravity of a liquid. NOT sugars. NOT starches. NOT dissolved baking soda. As brewers, we assume that the only thing affecting SG is sugar, because that's the only assumption we CAN make.

Dissolved salts in your brew water will have an effect on SG. Test your hydro with distilled water and with your city water. there will be a difference.

 

[The Pol]

You do realize that you and shortyjacobs said the exact same thing. His point was that hydros measure SG only, NOT sugar, NOT salt, NOT starch... but ANYTHING that will change the SG of water, they arent specific. He said, what you said.

The only assumption we can make though, is that the SG reading, is sugar... because that is the only assumption we can make. Same goes for a refract.

 

[oldschool]

I didn't realize that. But i do know that i really like arguing...

 

[Reno_eNVy]

I didn't realize that. But i do know that i really like arguing...

Man, you sure do hide it... I never would have noticed. Asking for advice and then telling the adviser why he/she is wrong must be one of your past-times, too.

 

[Kaiser]

The only assumption we can make though, is that the SG reading, is sugar... because that is the only assumption we can make. Same goes for a refract.

And there is nothing wrong with that. In fact, the Plato and SG tables that we use for determining efficiency, attenuation and alcohol are based on pure suugar solution.

Technically, the extract content in wort or malt, which we calculate for efficiency or malt analysis, is the weight of sucrose that would make a sugar solution with the same specific gravity if the same amount of water is used. Luckily we always use the same reference and the actual weight of extract is pretty close to that of sucrose which is why it works so well.

Kai

 

[TexLaw]

Hey, OP, here are a couple things to keep in mind:

1 -- You don't need medical grade iodine. In fact, that is getting pretty hard to find easily, since everyone is afraid you are heading off to our happy meth lab when you leave the store. Iodophore works great for the test, though, and that is easy to find. I typically add two parts water to one part iodophore (roughly -- it's a small amount) so that the iodophore and mash tun liquor mix a little easier. It's a fairly simple thing to do.

2 -- Another good way to check conversion (or lack thereof) is with your finger. Dip it into the mash tun and then taste it. If the liquor tastes starchy, don't even bother with an iodine test, as you are not done. If it's getting sweeter and a bit sticky, you may be onto something.

3 -- A refractometer is handy for checking conversion, but only as another tool that gives limited information. If your refractomer reading from the MLT liquor is low (say, you get a 12 when you're working on a beer with an OG of 1.056), then you shouldn't be done. It's actually somewhat fun to watch the refractometer readings increase as the mash converts. The refractometer certainly isn't a gold standard, but it's interesting. Stick with the iodine test if you want the best answer on conversion (or your finger).

Okay, gents, resume your hijack.


TL

 

[oldschool]

Man, you sure do hide it... I never would have noticed. Asking for advice and then telling the adviser why he/she is wrong must be one of your past-times, too.

Uh...yeah, thanks for the input. And just because someone tells you something doesn't mean they are correct.

 

[Catt22]

Man, you sure do hide it... I never would have noticed. Asking for advice and then telling the adviser why he/she is wrong must be one of your past-times, too.

It's a Southern Indiana thing! I've run into that before on more than one occasion.

 

[ClaudiusB]

Kaiser wrote:
give the test on chalk a try. It is so much easier to read and you can even tell color nuances. Preparing a series of iodine tests during the mash (every 10 min for example) is a great way to learn how conversion progresses and how the iodine reaction changes.

Kaiser's method is the way to go.
Even an old dog like me can use a better method than the old German way.

To compare the color change better, each component is put in one compartment and the wort iodine mix in the other.
The old way.,

I built a simple Kaiser gadget:

Cheers,
ClaudiusB

 

[oldschool]

Great display! Best post on this thread yet.

 

[dantodd]

Uh...yeah, thanks for the input. And just because someone tells you something doesn't mean they are correct.

If you will only accept self-reinforcing statements there is no need to ask the question. If you had considerable knowledge and wanted more then it is one thing to ask further questions but you did not even understand the basics of "what" a refractometer and iodine test do yet rejected the answers you received out of hand.

 

[Kaiser]

Claudius, you disappoint me. I would have expected something with a digital readout from you.

But seriously, thanks for giving the chalk a try. After all, I found this in a German textbook and after trying it myself I was wondering why I haven't heard of that before.*

Kai

 

[RighteousFire]

Iodine can only indicate wether or not there is starch present in a solution. We can not tell how fermentable the wort is until after fermentation is complete. As was said, this doesn't indicate if long or short chain sugars are present, just that there is sugar. No tool that a homebrewer, or microbrewers that I know, has can determine that. You would need a dedicated lab with appropriate equipment and training for that. Iodinde tests are an important part of the brewing process to determine conversion, and an easy thing you can do to be consistant.

A refractometer is used to determine a concentration of a given solution, and it is calibrated based on a pure solution. It doesn't matter what it's intended use is it will give a reading based on a physical constant of the refractability of a particular solution (sugar, starch, coolant, etc).

The beauty of a refractometer is you don't need to take a sample and chill it for an accurate reading. The small amount required will cool down fast enough to give an accurate reading. This means you can pull a sample from any part of the brewing process, pre-fermentation. You need a hydrometer for post fermentation gravity readings.

Hydrometers measure the gravity of a solution. Again, the hydrometer doesn't care what is in the solution wether it is salt or sugar or sand or dirt or anything. All it is telling you is the density of a liquid compared to pure water @1.000.

Dissolved salts in your brew water will have an effect on SG. Test your hydro with distilled water and with your city water. there will be a difference.

We as brewers assume that the only thing effecting the gravity reading is sugar, which is mostly true. Yes the TDS (total dissolved solids, usually mineral content) will have an effect on the reading but they usually, unless you have uber hard water, make up roughly .001% to .05% of the solution, which will really not play into your SG readings enough to matter. We aren't supposed to worry about these things, remember?

For the OP and anyone else out there in radio land I'm going to be brewing a pilsner this evening so I will do a series of iodine tests to show how it is done and what it looks like because everybody new seems to be lost when it comes to iodine. There will be pictures at least, and I will be taking video of the process and hopefully will have those uploaded shortly thereafter.

P.S. All the pro brewers I've met use a refractometer, hydrometer, and iodine in the same exact way we would. *

 

[Kaiser]

*We can not tell how fermentable the wort is until after fermentation is complete.

I’d like to point out that we can tell the fermentabily of the wort after a fermentation is complete. This doesn’t have to be the primary fermentation. Commercial brewers and many home brewers rely on a fast fermentation test to give them quick (2-3 days) feedback on the fermentability of the produced wort.

Kai

 

[RighteousFire]

I’d like to point out that we can tell the fermentabily of the wort after a fermentation is complete. This doesn’t have to be the primary fermentation. Commercial brewers and many home brewers rely on a fast fermentation test to give them quick (2-3 days) feedback on the fermentability of the produced wort.

Kai

A very good point.

 

[Boerderij_Kabouter]

The best description of how to use the iodine test (that I have read anyway) is in New Lager Brewing by Greg Noonan (RIP). He goes into detail about how specific color changes in the iodine indicate various stages of conversion.

oldschool, if you have a question and want an answer, go ahead and start new threads. If you want self satisfying answers, go talk to your mother. If you want to debate, go to the debate section. Starting a thread, getting clear answers, then rebuking those answers is not so cool.