Use of refractometer in lieu of time to determine when brew steps are complete

[TWS]

If one is intent on brewing to style, what are the drawbacks to using a refractometer to determine when to conclude the mash (upon reaching pre-boil gravity) and likewise conclude the boil (upon reaching OG)? Seems like this practice would help to standardize the output and potentially save time in the brew day.
Your collective thoughts?

 

[Minbari]

If one is intent on brewing to style, what are the drawbacks to using a refractometer to determine when to conclude the mash (upon reaching pre-boil gravity) and likewise conclude the boil (upon reaching OG)? Seems like this practice would help to standardize the output and potentially save time in the brew day.
Your collective thoughts?

Nothing wrong with it, pre-alcahol a refractometer will work fine.

Only drawback I can think of. If you go strictly by gravity to know when the mash is done, you would have to make sure you have exactly the right amount of water or it will be wrong and your starches might not be converted as you think.

 

[dmtaylor]

The trouble is: evaporative effects. Regardless of what many idiots will tell you about Automatic Temperature Correction (ATC) and the like, the fact is, a refractometer does not read accurately with a steaming hot sample. Even when you leave a hot sample to cool off a little bit, it is cooling by evaporation, which increases the sugar concentration, causing further inaccuracy and unpredictability, since sugar does not evaporate while the water vapor comes off. You could TRY to get accurate readings from hot samples by keeping cups cold in your refrigerator and drawing a tiny sample into a cold cup so that it is instantly cooled close to room temperature. But if this isn't done consistently, measurement might still be a crapshoot. I mean..... I'm a scientist, and I've tried to do things like this to make it work, but... real-life results have been surprisingly inconsistent to the point where I no longer bother trying to measure samples that started hot because.... it ain't easy to do it right.

 

[Donoroto]

As mentioned, there are error sources to consider.

If I wanted to brew closely to style, I'd brew a hair higher and then dilute with sterile water after it is all cooled, ignoring volume for the most part.

 

[The Brew Mentor]

Also, knowing your ingredients and equipment is the best way to predict the outcome.
And even then, I'd argue that you can't tell the difference in 2 or 3 gravity points.

 

[Craigerrr]

I think that is a perfectly acceptable method.
After drawing a small sample into a cool glass measuring cup, I draw some into a pipette and squirt it onto the refractometer.
I give it 30 seconds or so for the temperature to normalize before reading.
So this all takes place in about 60 seconds, I would be surprised if evaporation has an effect in this time.
If it did, it probably wouldn't make a discernable difference.

 

[BarbarianBrewer]

If I am mashing (in the kitchen) I'll put the wort into a 6 oz (175 ml) Pyrex dish and put that in the freezer to cool quickly. I fill it about a 1/4-1/3 full so I don't think the volume loss will be a significant percentage. Similarly when I'm outside boiling I'll let the sample cool in the Pyrex dish for a few minutes then put a few drops on the refractometer, close the cover and put is aside for a few more minutes. I figure with this method I'm not loosing too much to evaporation.

 

[Minbari]

I think that is a perfectly acceptable method.
After drawing a small sample into a cool glass measuring cup, I draw some into a pipette and squirt it onto the refractometer.
I give it 30 seconds or so for the temperature to normalize before reading.
So this all takes place in about 60 seconds, I would be surprised if evaporation has an effect in this time.
If it did, it probably wouldn't make a discernable difference.

Same here. I use a pipette to draw a 3ml sample and put two drops on the prism. By the time I close the lid, it's cool enough

 

[HighVoltageMan!]

I think that is a perfectly acceptable method.
After drawing a small sample into a cool glass measuring cup, I draw some into a pipette and squirt it onto the refractometer.
I give it 30 seconds or so for the temperature to normalize before reading.
So this all takes place in about 60 seconds, I would be surprised if evaporation has an effect in this time.
If it did, it probably wouldn't make a discernable difference.

I find this works very well. My numbers are consistent.