Iodine tests

oldschool · 10-12-2009, 08:36 AM

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** · 10-12-2009, 09:12 AM

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 · 10-12-2009, 02:31 PM

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)

Quote:

Originally Posted by Kaiser

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 · 10-13-2009, 02:43 AM

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** · 10-13-2009, 02:45 AM

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:

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

oldschool · 10-13-2009, 02:48 AM

Quote:

Originally Posted by 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:

http://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 · 10-13-2009, 02:53 AM

Quote:

Originally Posted by oldschool

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 · 10-13-2009, 03:06 AM

Quote:

Originally Posted by The Pol

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 · 10-13-2009, 03:12 AM

Quote:

Originally Posted by oldschool

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** · 10-13-2009, 03:17 AM

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.