Consistency, Efficiency, and Squeezing the Bag

[AlexKay]

Is the wort pressed out of the bag while squeezing the same gravity as the wort already in the pot?

I'm trying to understand my SG measurements today, which were 1.030 at the end of the mash (with the bag and grain still in the pot) and 1.040 after I'd removed and squeezed the bag. (The wort seemed to taste sweeter, too, though it's hard to be sure.) Refractometer both times, on cooled wort.

If the squeezed-out wort actually was higher gravity, I'd think this would cause consistency problems, since the overall SG would depend on how hard one squeezed the bag. (And, as it happens, I do have consistency problems.)

Is this crazy? Am I crazy?

 

[DBhomebrew]

Did you thoroughly mix the mash just before pulling the 1.030 sample?

 

[palmtrees]

I have found this to also be the case, the one or two times I measured before pulling the bag and then after. I didn't necessarily attribute it to water outside the bag versus inside. I had assumed that I probably had stratification within my mash, since high gravity wort should be heavier than low gravity wort. And it can be difficult to get things really mixed well when the grain is in the water. But there definitely might be some difference in gravity between the wort left in the pot and the wort squeezed from the bag, since the grain itself is the source of the sugar. Next time I brew, I might test things by taking a reading of the wort in the pot before i pull, the wort left after I pull, and then the runnings from the squeezed bag.

Regarding consistency, I bet you can minimize any impact this has by doing the same process every time. For example, every brew, I put my bag in a colander and let it naturally drain for a while, then squeeze the bag as much as possible with a metal spoon. I don't notice any consistency issues that I would attribute to the squeeze. My mash temps seem to have a much bigger impact.

 

[odie]

unless you are doing recirc during the mash...I can easily see the sample from outside the bag being lower.

If you had mixed well and kept the mash circulating then all the samples should be uniform.

but what matters is the SG after the bag is drained and your wort thoroughly mixed.

 

[AlexKay]

It could be poor mixing. There's no recirculation, and all I did was stir (somewhat vigorously) with a spoon before pulling a sample.

I do try for consistency, but squeezing "as hard as I can" seems like something that could change from brew day to brew day. And my numbers do fluctuate 10% or 20% from batch to batch.

 

[doug293cz]

Is the wort pressed out of the bag while squeezing the same gravity as the wort already in the pot?

I'm trying to understand my SG measurements today, which were 1.030 at the end of the mash (with the bag and grain still in the pot) and 1.040 after I'd removed and squeezed the bag. (The wort seemed to taste sweeter, too, though it's hard to be sure.) Refractometer both times, on cooled wort.

If the squeezed-out wort actually was higher gravity, I'd think this would cause consistency problems, since the overall SG would depend on how hard one squeezed the bag. (And, as it happens, I do have consistency problems.)

Is this crazy? Am I crazy?

There are two things that can make the squeezed wort higher gravity than the initially drained wort:

1. All the wort in the mash was not homogenized prior to initial draining. Due to the mechanics of gelatinization and conversion, the wort at the surface of the grits will normally be higher in sugar concentration (higher SG) than the bulk of the wort (not in direct contact with the grits.) In a straight BIAB (bag completely fills the mash vessel) this can be remedied by aggressive stirring of the mash prior to pulling the bag. In a system with a mash/malt pipe, where you have wort outside/under the pipe, then stirring the mash inside the pipe is ineffective at homogenizing the wort. People have had success with wort mixing by lifting and draining the pipe, reimmersing the pipe completely, stirring, and repeating a few times.
2. The conversion of starch to sugar was not complete when the draining started. In this case additional conversion can occur in the mash prior/during squeezing. The additional sugar created, prior to the end of the squeeze, will make the SG of the squeezed wort higher. You can remedy this by mashing longer, or doing a mash out. The mash out is functionally an extension of the mash time - at increased temperature that increases the rate of gelatinization and conversion (until all of the amylase enzymes are denatured.)

Brew on

 

[Birrus]

What they've said. Assuming conversion is done, if you thoroughly mix the wort before pulling the bag out, gravity should be uniform throughout the mash; and how much you squeeze the bag should not change this. On a side note; consistency is achieved by following the same routine every time you brew, especially where your process affects parameters which have an impact on the resulting starting gravity (thus, efficiency). If you normally have a variation of 10-20% in SG from what you've calculated, try adopting a method that ensures you do the same every time you brew, and change the efficiency used to calculate your recipes to approximate what you get in reality. FWIW, I always "rinse" (at this point I don't really know how to call this, "mash out" I guess ) the grains in the bag after pulling it out. I use a gallon or two of water @ 170 F, and simply let it drain in a colander when done. I know what efficiency I get with this system, and that's what I use on calculations, darn being concerned for what's left in the bag when pulled out.

 

[odie]

It could be poor mixing. There's no recirculation, and all I did was stir (somewhat vigorously) with a spoon before pulling a sample.

this is why...nothing more, nothing less...

 

[beerisyummy]

What I have been doing is similar to Birrus... I do da mash in da bag. Then, after draining the bag a bit I do a dunk sparge in about 2 gal of 170° water. Drain the bag again in a colander over the dunking pot, then squeeze. For the squeeze I use three 5 gallon buckets. The middle one has holes drilled in it, I stand in the top one to squish it, and it drains into the bottom one. I combine the sum total of the mashing, dunking, and squeezing, all in the kettle, then measure gravity BEFORE topping up the volume for the boil (if needed). I'm not sure why I should be interested in gravity readings of any of the individual steps. Seems to work.

 

[doug293cz]

What I have been doing is similar to Birrus... I do da mash in da bag. Then, after draining the bag a bit I do a dunk sparge in about 2 gal of 170° water. Drain the bag again in a colander over the dunking pot, then squeeze. For the squeeze I use three 5 gallon buckets. The middle one has holes drilled in it, I stand in the top one to squish it, and it drains into the bottom one. I combine the sum total of the mashing, dunking, and squeezing, all in the kettle, then measure gravity BEFORE topping up the volume for the boil (if needed). I'm not sure why I should be interested in gravity readings of any of the individual steps. Seems to work.

You are better off, from a lauter efficiency standpoint, squeezing the bag before you sparge, rather than after you sparge. The less sugar left in the grain mass before the sparge starts, the less sugar will be left after the sparge.

The reason to measure your end of mash SG (prior to adding any sparge water) is to be able to calculate your conversion efficiency. Mash efficiency is equal to conversion efficiency times lauter efficiency. If you have efficiency issues, you need to know your conversion efficiency and lauter efficiency, not just your mash efficiency, in order to know where your problem originates.

Brew on

 

[beerisyummy]

You are better off, from a lauter efficiency standpoint, squeezing the bag before you sparge, rather than after you sparge. The less sugar left in the grain mass before the sparge starts, the less sugar will be left after the sparge.

The reason to measure your end of mash SG (prior to adding any sparge water) is to be able to calculate your conversion efficiency. Mash efficiency is equal to conversion efficiency times lauter efficiency. If you have efficiency issues, you need to know your conversion efficiency and lauter efficiency, not just your mash efficiency, in order to know where your problem originates.

Brew on

Hmmm good point. I'm measuring my pre-boil gravity then which ≠ mash efficiency.
Soooo .... should the pre-sparge bag squeezings be included in the gravity reading to determine mash efficiency?

 

[doug293cz]

Hmmm good point. I'm measuring my pre-boil gravity then which ≠ mash efficiency.
Soooo .... should the pre-sparge bag squeezings be included in the gravity reading to determine mash efficiency?

Pre-boil SG (after a good mixing) and pre-boil volume are used to determine mash efficiency, in combination with grain bill weight and grain bill potential.

Mash efficiency can also be determined from post boil SG (aka OG) and post boil volume, as long as you didn't add any fermentables after the mash.

Conversion efficiency is calculated from end of mash boil, strike water volume, grain bill weight, and grain bill potential.

Lauter efficiency is calculated as: Lauter Efficiency = Mash Efficiency / Conversion Efficiency.

Brew on