Gravity without conversion?

[McCoy]

I think I know the answer to these question but I want to be certain. Specific gravity is only based on dissolved particles in the wort, changing its density.

Is conversion necessary to alter the gravity? (I think the answer is no.)

Shouldn't the starch itself change the gravity before conversion? (I think yes.)

Would a gravity reading taken before conversion is complete, but after all the starches are thoroughly dissolved in the wort, be an accurate measure of pre-boil gravity? (I'm really now sure, but I think yes.)

 

[Shred]

I don't believe so. When you steep grains in extract beers they have very little impact on the gravity.

 

[McCoy]

Presumably the starch has the same mass as the maltose/dextrins/other sugars it is decomposed into by the enzymes. If the starch is really dissolved in the wort, I fail to see why it wouldn't change the gravity by the same amount as the sugars the result from their decomposition.

 

[Shred]

Honestly, not sure. What you're saying seems to make sense. I guess the reason I'd seen little impact from steeped grains in extract brews was probably because of the low percentage of grain to extract used and the shortened mash/steep time.

 

[unionrdr]

I'm not inclined to think that conversion changes gravity,So gravity isn't a way to check conversion convbersely. you need a test kit for that. And what you get from steeping grains doesn't have to be fermentable to change graivity,in my opinion/experience. Long chain sugars that give color & flavor aren't without mass. So they must effect gravity. but just things that are dissolved into the liquid. Not things in suspension.

 

[Phunhog]

I have thought about this before and my conclusion is that your gravity reading is indeed an indicator of whether you have conversion. I use a refractometer and can watch my SG climb during a one hour mash. A refractometer only can measure sugar...not starch or anything else. Even if ou used only a hydrometer I think it is a good indication of conversion since my hydrometer and refractomer are usually pretty close to each other.

 

[McCoy]

I have thought about this before and my conclusion is that your gravity reading is indeed an indicator of whether you have conversion. I use a refractometer and can watch my SG climb during a one hour mash. A refractometer only can measure sugar...not starch or anything else. Even if ou used only a hydrometer I think it is a good indication of conversion since my hydrometer and refractomer are usually pretty close to each other.

Hydrometers and refractometers measure fundamentally different things. Hydrometers measure density while refractometers measure index of refraction. The starch and the sugars they are broken down into must conserve mass, so the dissolved starch and dissolved sugars should have the same gravity. Meanwhile, because sugars and starches are molecules of different size, conformation, etc. they could have very different indices of refraction. Therefore, it is feasible that starch and sugars are distinguishable using a refractometer, though I am not sure how.

Something that surprises me given my line of argument is that if the SG doesn't discriminate between starch and sugar, then the fact that SG continues to rise in the mash (e.g. you get more extract with a 90 minute mash than a 60 minute mash) would imply that you are in fact continuing to dissolve starch into the wort late into the mash. If that were true, it would surprise me that you'd ever pass a conversion test. Perhaps the conversion test just isn't very sensitive -- like it could detect if 10 points of starch remained unconverted but not 1 or 2 points.

 

[clskinsfan]

I have thought about this before and my conclusion is that your gravity reading is indeed an indicator of whether you have conversion. I use a refractometer and can watch my SG climb during a one hour mash. A refractometer only can measure sugar...not starch or anything else. Even if ou used only a hydrometer I think it is a good indication of conversion since my hydrometer and refractomer are usually pretty close to each other.

Amen. Great post!!

 

[savannahbrew]

I believe it would absolutely change the gravity. It is not as simple as x grams of sugar in 1 liter is equal to x grams of carbohydrates in 1 liter. In chemistry the density of a solution (wort, beer, whatever liquid mixture) is the sum of the mass concentrations of all the components which make up that solution.

 

[GuldTuborg]

I have thought about this before and my conclusion is that your gravity reading is indeed an indicator of whether you have conversion. I use a refractometer and can watch my SG climb during a one hour mash. A refractometer only can measure sugar...not starch or anything else. Even if ou used only a hydrometer I think it is a good indication of conversion since my hydrometer and refractomer are usually pretty close to each other.

The SG changes over time as more stuff gets dissolved in the wort. Some of that will be sugar, some will not. It is not a good indication of conversion.

Point is, hydrometers do not measure only sugar. If you don't believe me, measure a sample of water. Then dissolve a bunch of salt in that same sample, and test gravity again. You're measuring dissolved solids in water (at least until alcohol enters into the equation), nothing else.

 

[Phunhog]

The SG changes over time as more stuff gets dissolved in the wort. Some of that will be sugar, some will not. It is not a good indication of conversion.

Point is, hydrometers do not measure only sugar. If you don't believe me, measure a sample of water. Then dissolve a bunch of salt in that same sample, and test gravity again. You're measuring dissolved solids in water (at least until alcohol enters into the equation), nothing else.

False. Here is how a refractomer works. http://www.grapestompers.com/refractometer_use.aspx
It can only measure sugar...it can't measure "stuff". If it did it would be close to worthless.
The same would apply to a hydrometer too I think. Otherwise why bother taking a gravity reading at all since it could be thrown off by a multitude of "stuff" in the wort (proteins, hop particles, etc.)? It would be a false number that you can't rely on for anything.

 

[Zinc_Saucier]

False. Here is how a refractomer works. http://www.grapestompers.com/refractometer_use.aspx
It can only measure sugar...it can't measure "stuff". If it did it would be close to worthless.
The same would apply to a hydrometer too I think. Otherwise why bother taking a gravity reading at all since it could be thrown off by a multitude of "stuff" in the wort (proteins, hop particles, etc.)? It would be a false number that you can't rely on for anything.

True, a refractometer can only measure sugar (to the best of my understanding) however that doesn't mean that taking a gravity reading with a hydrometer during mashing would give you an accurate measure of starch-->sugar conversion. http://en.wikipedia.org/wiki/Specific_gravity if you check the end it shows the gravity of a lot more that sugar. So maybe a refractometer would be good to check conversion, but I don't think a hydrometer is the way to go.

Just my $.02

 

[GuldTuborg]

False. Here is how a refractomer works. http://www.grapestompers.com/refractometer_use.aspx
It can only measure sugar...it can't measure "stuff". If it did it would be close to worthless.
The same would apply to a hydrometer too I think. Otherwise why bother taking a gravity reading at all since it could be thrown off by a multitude of "stuff" in the wort (proteins, hop particles, etc.)? It would be a false number that you can't rely on for anything.

OK, several things are wrong here.

First, I never said anything about refractometers in my post, you you can't claim I said anything "false" by talking about them. Since you brought it up, I'll go there.

We use both hydrometers and refractometers measure the same thing, through different means (and some conversions have to take place). Did you bother to use your instruments to measure salinity, like I suggested? If you did, you'd see that I'm correct, and have provided a very easy to observe and understand counterexample. Seriously, try it. Your statement that these instruments only measure sugar is 100% false.

Consider this: when both instruments are calibrated, distilled water must be used, right? That's because the unknown amounts of dissolved solids in other types of water make it unusable to calibrate with. You could calibrate an instrument with other types of water, if you knew exactly the density or refractive index of the solution, but it's rare that we have anything like that on hand.

If you can't bother with taking 5 minutes to drag out your equipment and try this, consider these points. The reason we can rely upon the measurements we do, even though we're measuring all dissolved solids, is that a properly made wort is mostly fermentable sugar, and we're generally not adding or taking away any dissolved solids other than what gets fermented. We make wort to be that way so it makes better beer, but it means that the gravity changes are mostly due to increases or decreases in sugars.

Since I said I'd talk about refractometers as well, look over this link. People who work with salt water aquariums and in ocean water environments use the very same refractometers we do to measure salinity. Refractometers are used in commercial industries, medicine, an other fields to determine the purity of a solution with known ingredients. Even the Wikipedia entry for refractometers states this. The only difference in the "types" of handheld refractometers is the difference in scale, which is tweaked to suit the needs of the user (i.e., the refractive scale measured and the assumptions and calculations that are used to determine what the "scale" looks like in the viewable readout). The base product is the same, and it measures optical refraction, nothing else.

This thread has good reading on the subject. See post #38 for a nice discussion of how these things work. These instruments are useful, but only to estimate the stuff we're really after. We have to know about other variables and make certain assumptions along the way.

 

[Wynne-R]

The point is, the starch is not in solution. So it doesn’t affect the density of the liquid.

You can throw a marble in there, it won’t change the specific gravity.

 

[GuldTuborg]

The point is, the starch is not in solution. So it doesn’t affect the density of the liquid.

You can throw a marble in there, it won’t change the specific gravity.

You're joking, right? Starches aren't soluble in water? How do you think mashing works? Starches from the barley dissolve in water, so do enzymes, then they get together and do their thing. The gravity changes as soon as things dissolve.

Next time you're brewing, try this crazy thing called an iodine test. Mash in, 5 minutes later draw a sample and add iodine. The worth will turn black as it reacts with the dissolved starches in the water. I'm not denying that insoluble starches exist, but that's not the point of this debate. Gravity changes or refractive indexes need not have anything in the world to do with starch conversion.

 

[GuldTuborg]

Sorry, OP. I've been so busy with the rest of this, um, discussion, that I never got around to giving actual answers.

Is conversion necessary to alter the gravity? (I think the answer is no.)

You're correct; conversion is not necessary.

Shouldn't the starch itself change the gravity before conversion? (I think yes.)

Yes, it does.

Would a gravity reading taken before conversion is complete, but after all the starches are thoroughly dissolved in the wort, be an accurate measure of pre-boil gravity? (I'm really now sure, but I think yes.)

This is where things get tricky. As long as we know nothing about the starch conversion process causes a reaction which creates an insoluble substance, then yes. I don't know that for a fact, but I can't think of anything that would play that role.

The other factor in this is the timing. How do you know when all the starches, proteins, and so forth are dissolved? I don't have an answer to this. Maybe there's an increase all the way through the process, but obviously slower as things go on. Maybe there's a point after which the increase in dissolved material is negligible for our purposes. I just don't know. I'd be curious to find out.

The third element of this is, why do you ask? Is it just curiosity, or is there a problem in your process you're trying to work out? If so, what is it?


Anyway, I hope this is helpful. It's also pretty straightforward stuff, and shouldn't really need any defense, but if I need to provide evidence on any point, I'm happy to do so. Let me know.

 

[Phunhog]

OK, several things are wrong here.

First, I never said anything about refractometers in my post, you you can't claim I said anything "false" by talking about them. Since you brought it up, I'll go there.

We use both hydrometers and refractometers measure the same thing, through different means (and some conversions have to take place). Did you bother to use your instruments to measure salinity, like I suggested? If you did, you'd see that I'm correct, and have provided a very easy to observe and understand counterexample. Seriously, try it. Your statement that these instruments only measure sugar is 100% false.

Consider this: when both instruments are calibrated, distilled water must be used, right? That's because the unknown amounts of dissolved solids in other types of water make it unusable to calibrate with. You could calibrate an instrument with other types of water, if you knew exactly the density or refractive index of the solution, but it's rare that we have anything like that on hand.

If you can't bother with taking 5 minutes to drag out your equipment and try this, consider these points. The reason we can rely upon the measurements we do, even though we're measuring all dissolved solids, is that a properly made wort is mostly fermentable sugar, and we're generally not adding or taking away any dissolved solids other than what gets fermented. We make wort to be that way so it makes better beer, but it means that the gravity changes are mostly due to increases or decreases in sugars.

Since I said I'd talk about refractometers as well, look over this link. People who work with salt water aquariums and in ocean water environments use the very same refractometers we do to measure salinity. Refractometers are used in commercial industries, medicine, an other fields to determine the purity of a solution with known ingredients. Even the Wikipedia entry for refractometers states this. The only difference in the "types" of handheld refractometers is the difference in scale, which is tweaked to suit the needs of the user (i.e., the refractive scale measured and the assumptions and calculations that are used to determine what the "scale" looks like in the viewable readout). The base product is the same, and it measures optical refraction, nothing else.

This thread has good reading on the subject. See post #38 for a nice discussion of how these things work. These instruments are useful, but only to estimate the stuff we're really after. We have to know about other variables and make certain assumptions along the way.

Thanks for the info. Now something is bothering me....the "stuff" you refer to. I often take gravity readings during the boil when there are still a lot of stuff(hop particles) floating around in the wort. Would the presense of those solids effect the gravity reading vs. taking a "clean" sample post-whirlpool? Obviously the more particles there are the denser the solution...I am thinking of "hop sludge" or even a yeast slurry.

Anyways back to the OP's question So I guess on technical level No you can't guarantee that a SG number equals conversion. I put some liquid soap on my refractometer on got 1.090 which obviously isn't fermentable. On a practical brewing level though Yes you can.

 

[Phunhog]

You're joking, right? Starches aren't soluble in water? How do you think mashing works? Starches from the barley dissolve in water, so do enzymes, then they get together and do their thing. The gravity changes as soon as things dissolve.

Next time you're brewing, try this crazy thing called an iodine test. Mash in, 5 minutes later draw a sample and add iodine. The worth will turn black as it reacts with the dissolved starches in the water. I'm not denying that insoluble starches exist, but that's not the point of this debate. Gravity changes or refractive indexes need not have anything in the world to do with starch conversion.

You bring up an interesting point. Is there a possibility of extracting starches into a solution but NOT converting them into sugars? What would make this possible? Low temperatures?Getting back to the OP's question.... As brewers what is the PRACTICAL application?

 

[GuldTuborg]

Thanks for the info.

Not a problem. I'm glad that all got cleared up. Looking around a bit, it seems to be a common misconception, and I can tell why. Every brewing/winemaking site out there refers to these devices as measuring sugars. In a sense, you are, only very indirectly, and with many assumptions and conversions happening between what you actually see happening with your device and what you then think about the sugars in your wort/must. I think it's good to be clear on the process, as it makes questions like the OP's easier to navigate.

Now something is bothering me....the "stuff" you refer to. I often take gravity readings during the boil when there are still a lot of stuff(hop particles) floating around in the wort. Would the presense of those solids effect the gravity reading vs. taking a "clean" sample post-whirlpool? Obviously the more particles there are the denser the solution...I am thinking of "hop sludge" or even a yeast slurry.

I think the answer is these can affect readings. Most of these particles you're talking about (large bits of hop sludge, etc.) never get dissolved, so they don't affect the density of the wort as such, but they can adhere to a hydrometer, and can affect the reading that way. That's why we're taught to spin the hydrometer to get a good reading; it releases gas bubbles, particulate matter, and other things that can stick to the hydrometer and give a skewed reading.

Then there are smaller bits, that might not dissolve as such, but can form a colloid. That's interesting because most of these particles are small enough to affect a reading, but heavy enough that many of them will fall out of solution into the trub eventually. This means that part of the typical OG->FG change has to do with these bits falling out of solution, and not fermentation. How much this affects everything probably has a lot to do with wort composition, exactly when you take measurements, etc. I'm afraid I just don't know enough to know how much of an issue this actually is. I guess it depends upon how precise you need your measurements to be. For most of us, we just want a feel for if fermentation went roughly as expected, and generally how much alcohol is in the beer, so I guess we can often ignore this aspect.

I also don't really know how much these factors affect the refractive properties of a sample, so I can't tell you how it will affect a refractometer. Part of me suspects that larger particulates will not affect the refractive index as much as completely dissolved solids, and readings might be a bit different than with a hydrometer, but that's pure conjecture on my part.

You bring up an interesting point. Is there a possibility of extracting starches into a solution but NOT converting them into sugars? What would make this possible? Low temperatures?Getting back to the OP's question.... As brewers what is the PRACTICAL application?

That's absolutely possible. Boil water, add grain. You've just made starch tea. The high temperatures will denature the starch quickly enough that there will be very little time or opportunity for conversion.

A low temperature might work, but there are two obviously complicating factors. First, the lower the temperature, the slower the starches will move into solution, and at those low temperatures, enzymatic activity does happen, just at a much slower rate than at the temperatures we mash at. I don't know which process would tend to happen faster, so maybe there would be a point where a significant amount of starch would be in solution before much conversion took place, or maybe there wouldn't. I'm sure you could find out by mashing at a cold temp and testing for starch every couple of minutes.

You could achieve the same with a pH that's way out of whack, or something akin to that. Basically, any element that makes the "wort" hostile to enzymes (hostile isn't the right word, as enzymes aren't alive, but I'm tired and can't think of a better one) would allow some level of starch into solution without conversion.

The practical application of all this is, don't let gravity alone be your sole determining element of if proper conversion took place. Under the right conditions (meaning, if you do everything else right) it is a helpful piece of the puzzle, but it's not the only one. Keep good data about your process, and bits like this will help you figure out what's going on in the event that there is a problem.

 

[McCoy]

Sorry, OP. I've been so busy with the rest of this, um, discussion, that I never got around to giving actual answers.

The third element of this is, why do you ask? Is it just curiosity, or is there a problem in your process you're trying to work out? If so, what is it?


Anyway, I hope this is helpful. It's also pretty straightforward stuff, and shouldn't really need any defense, but if I need to provide evidence on any point, I'm happy to do so. Let me know.

Thanks for your answers. I think the side discussion was also useful. Even though I knew the physical mechanisms by which the instruments worked, it's still good to have you intuitions confirmed.

My question was really out of curiosity. I'm a physicist and tend to think about measurements a lot, especially since so often we have to measure something a proxy for quantity we're actually interested in. I like to reconcile many of my everyday activities with my scientific intuitions, and this week my curiosity was sparked when I was mashing and wondering if there was a way to get a better picture of what my pre-boil gravity would be earlier on in the process, and if there was any way to know if/how much of the dissolved solids were fermentable other than by an iodine test.

Oh, and more specifically, I wasn't really thinking about continued dissolution of starches into solution (the rate should probably decay exponentially with some time constant that might be possible to measure in a mash by just taking repeated gravity readings) and was instead thinking of all the starches dissolving right away. That's obviously a silly way to think of it, but at the time was causing me to puzzle over how one could end up with differing mash efficiencies.

 

[GuldTuborg]

Oh, and more specifically, I wasn't really thinking about continued dissolution of starches into solution (the rate should probably decay exponentially with some time constant that might be possible to measure in a mash by just taking repeated gravity readings) and was instead thinking of all the starches dissolving right away. That's obviously a silly way to think of it, but at the time was causing me to puzzle over how one could end up with differing mash efficiencies.

That makes sense. As for differing mash efficiencies, I suppose there are several factors that might explain it. The crush may allow more or fewer particles to get mixed into solution or suspension, based on how much the water is able to penetrate the grains over time. I imagine a good many larger starches do get suspended in the wort during mashing, but would fall out if not converted to something smaller that could dissolve (or form a colloid) eventually. Maybe much of this does depend upon when and how we take a sample.

Perhaps there are other factors at work, too. I'm sure estimations involved in water measurement for the mash affect things, and do cause some differences. Lautering and sparging methods definitely will affect OG measurements, unless you're talking about the gravity of the first runnings. Maybe something about the enzymatic process helps free some starch/sugar molecules from the grain itself, that otherwise would not be in solution. I wish I understood these processes better. I'm just guessing here, really.

 

[McCoy]

It definitely gives one an appreciation for the fact that there are people who get advanced degrees in brewing science.