Question about gravity, mash temp and wort fermentability

[CHans3]

Today I did my third brew in a bag attempt of a pale ale I am trying to dial in. The malt bill has been the same every time, only hop additions are different. First time I was way off my og. Last time it went perfectly. I hit all of my numbers and I am drinking the beer now.

This time around, my pre boil gravity was off about twelve points. I added some starter dme I had to get to my correct post boil og, but it got me thinking. This time, I focused more on proper mash temperature versus stirring the mash a lot. Mash in temperature was 153 and after an hour it was still at 150. I only stirred it when mashing in. Previously when I got good efficiency, I stirred quite a bit but my final mash temp was about 140. Next time, I will likely focus on stirring a bunch and squeezing the hell out of the bag to hit my numbers.

Sorry for the long winded post, but this all led me to think about mash temperature, gravity and wort fermentability. If I mash high, and have less fermentable sugars in my wort versus I larger amount of fermentable sugars, does this result in a lower gravity of the wort? In other words, is gravity like a colligative property from the stand point that it is related to the amount of molecules in solution but not the kind of molecules?

Cheers,

Chans

 

[unionrdr]

Basically,the higher the temp,the less fermentable sugars you get. Stirring the dough balls out of the mash & getting it all evenly wetted is important to higher efficiency. And thus,higher OG.

 

[Ondori]

I have never done brew in a bag, but I brew AG, and I watched the episode of BTV on BIAB. I know when I mash, I stir the hell out of it, and I even give my mash tun a few rocks every 20-30 minutes to get the liquid moving. In the episode I saw they did a mini sparge, by just pouring some hot water (close to 170) over the grain bag while they had it propped up with a strainer. I would try to do a little sparge next time instead of squeezing the bag.

 

[unionrdr]

I sparge mine with 1.5 gallons of 165F water. This after mashing 5lbs of grains in 2 gallons of water at 152 for 1 hour. It's PB/PM BIAB by the way...

 

[CHans3]

I know what you guys are saying. I will focus on stirring more next time and I always sparge with about three gallons of water.

The question is whether or not gravity is dependent on the amount of sugar in solution? Ie: if I pour the same amount of starch into two solutions, mash one at 154 and the other at 146, will I see a difference in gravity? If I break down the sugars in one solution more than those in the other, I will see a difference In gravity right?

This is a very geeking out on beer question, but I am just trying to understand the process better.

 

[CHans3]

This question stems from whether or not my lower gravity resulted from less stirring or from the fact that more stirring led to a greater temperature loss and therefore a lower gravity.

 

[climateboy]

The closer your temperature is to 148, the more fermentable sugars you will have. The starting gravity (SG) can be the same at 156 or 148, but the mash at 148 will result in a lower FG, because it is a more fermentable wort. If you drop much below 146, the enzymes will not really activate and you will have a lower SG because there hasn't been much conversion.

Stirring makes a difference to the extent that all the grains have gotten wet with the appropriate degree water, so conversion will obtain. It also makes a difference in evening out the temperature of the mash. If you don't stir well, you could potentially have one portion of the mash at conversion temperature, and other portions that are below conversion ranges.

Another thing that can affect conversion is mash thickness. If you mash too thin, the enzymes are too dilute, and don't get the contact with the starches necessary for conversion.

Does that help?

 

[CHans3]

That is interesting about mash thickness. Maybe I will try mashing thicker next time.

I understand the mash temperature versus wort fermentability thing. The question is if I have the same amount of maltose molecules in one solution and the same amount of a more complex sugar in another solution, will they read the same gravity? Is gravity fundamentally a measure of the amount of molecules in solution independent of the type of molecule?

 

[unionrdr]

Gravity basically measures the amount of sugars in solution,not fermentability.

 

[climateboy]

Gravity basically measures the amount of sugars in solution,not fermentability.

That's correct. The hydrometer or refractometer doesn't know what kind of sugar you have in there, just that there are sugars.