Author Topic: Iostar to measure starch?  (Read 2825 times)

Offline davidgzach

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Re: Iostar to measure starch?
« Reply #15 on: November 30, 2012, 06:31:02 AM »
So Jeff, do you perfrom an iodine test on every brew or just those that have a more complex malt bill?

Dave
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Offline hopfenundmalz

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Re: Iostar to measure starch?
« Reply #16 on: November 30, 2012, 06:37:37 AM »
So Jeff, do you perfrom an iodine test on every brew or just those that have a more complex malt bill?

Dave

Some we have done this fall were so clear, no need to. Sometimes the wife does it just because. If we have doubt, it is done as a go/no go test. Usually the result is to go ahead. The ones it has said not to go ahead on were high in dark munich malt. Now I have been adding 15 to 20% Pilsner to get some higher enzyme levels.

My wife was an elementary teacher. She would do the iodine on the potato test with the kids for science class, so she likes doing the iodine test, takes her back I think.
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Offline Kaiser

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Re: Iostar to measure starch?
« Reply #17 on: November 30, 2012, 07:10:01 AM »
Maybe an iodine test is like parallel parking, unless you live in the city you rarely need it. Brewers should learn how to do the iodine test correctly but most of the time it is not needed.

The problem is that it doesn't show you how well you mash converted the starches from the malt. For that you need to do a mash gravity test for conversion efficiency. I have a table here that shows what mash gravity to expect when all starches convert. I also worked with Larry from Brewer's Friend to integrate that into BF's log entries and have it report conversion efficiency. I also have a spreadsheet for this, but I'm finding it easier when the grain and water data comes directly from the recipe.

Like Jeff, I have found that dark beers tend to need more attention when it comes to conversion. They are sometimes slow to get into the mid to upper 90's with respect to conversion efficiency.

Kai

Offline hopfenundmalz

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Re: Iostar to measure starch?
« Reply #18 on: November 30, 2012, 07:54:24 AM »
Hey Kai - I have been using your table this fall for checking conversion eff.

Though I would give kudos for that.

The iodine test does not say what the sugar content is, it just says the starch has converted. It does not say into what. Conversion takes place quickly, to get the most out of the mash takes 60 to 75 minutes.
« Last Edit: November 30, 2012, 09:15:32 AM by hopfenundmalz »
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Offline davidgzach

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Re: Iostar to measure starch?
« Reply #19 on: November 30, 2012, 08:07:45 AM »
Good info guys, thanks!
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Offline neemox

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Re: Iostar to measure starch?
« Reply #20 on: November 30, 2012, 09:00:42 AM »
So my opinion had been that a starch test could work as the go/no go as Jeff and others pointed out. There isn't a way to measure efficiency before you start lautering, right? In my head, I'm imagining that pulling wort off the top of the grain bed is going to be different than the wort under the grain, but maybe I'm not thinking clearly in the morning. Would it be a good idea to dip enough wort out of the mash to take a gravity reading before I start lautering?  Using Kai's chart and this gravity (assuming I let it cool before reading it) would eliminate the need for an iodine test.

Do people do this?

Offline Kaiser

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Re: Iostar to measure starch?
« Reply #21 on: November 30, 2012, 09:34:11 AM »
There isn't a way to measure efficiency before you start lautering, right? In my head, I'm imagining that pulling wort off the top of the grain bed is going to be different than the wort under the grain, but maybe I'm not thinking clearly in the morning. Would it be a good idea to dip enough wort out of the mash to take a gravity reading before I start lautering? 

Yes there is a way to measure the efficiency before you start lautering. But not in the conventional way since you don't know the volume of the wort in the mash. But one can determine the amount of sugar that has been dissolved based on the volume of water that was used and the current gravity of the wort. That is the idea behind the mash gravity test. But as you pointed out, the mash needs to be well mixed for that. Just like the kettle wort has to be well mixed before you can take a pre boil gravity measurement.

Quote
Using Kai's chart and this gravity (assuming I let it cool before reading it) would eliminate the need for an iodine test.

Do people do this?

I do this all the time. More than the iodine test. If I expect 80+% efficiency from my batch sparging process I know that my conversion efficiency has to be in the high 90's. If it is not I have a few options:

- let it mash for longer (I commonly do this)
- raise the temp to boost a-amylase (I also do this when needed or as part of the mash schedule)
- add more malt (I would only do this if I suspect low enzymatic strength to be the culprit. In that case I'd add pilsner malt)
- decide to go two batch sparges instead of one (this compensates for low conversion efficiency by boosting lauter efficiency, but that may have a negative impact on beer flavor)
- don't do anything

You don't have these options if the only place you test for efficiency is the boil kettle.

The iodine test checks for starch in the wort. If your conversion efficiency is close to 100% I would be surprised if the iodine test is positive. But if you have conversion issues you may have low conversion efficiency which you could compensate for by adding more grain. But even if you do that you need to make sure that the wort that is boiled is iodine negative unless the beer needs starches and long dextrins for character (e.g. Wit and other Belgians).

As I said before, I do the iodine test on the wort that I run into the kettle when I brew Doppelbocks and Dunkels just to make sure that the boiled wort will be starch free.

Kai