Ask The Brewmasters

Hi Brewmasters,

I'm sure this question has been posed before but I couldn't find the answer. We are seeing a reasonably wide range of stratification in our boil kettle when taking gravity readings post boil. We are using a digital refractometer that is calibrated daily as well as a pH meter calibrated at least every brew day. Our method is to pull 3-4 samples post whirlpool and rest as we transfer to our fermenter, usually at approx 10BBLs remaining (full), 7BBLs remaining, 5 BBLs remaining and 3 BBLs remaining (usually approximately 20 minnutes between first and last reading. The samples are pulled (temp usually around 185F) and cooled to room temp so readings are uniform and evaporation rates a minimal. We typically see pH's within an acceptable range across the samples (+/- 0.03). However, we see a wider range on our gravities. Yesterday we had readings of 16.2, 16.4, 17.1 and 17.2P. We typically just average out the samples but I'm not sure how accurate this is. I wanted to see if anyone had an ideas of best practices when pulling samples or ideas about best way to determine a uniform gravity reading, unless averaging across several samples is best. Thanks in advance! Cody

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Cody Higginbottom
Denver CO
(303) 917-3000
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Cody,

I see that you have a 10-bbl kettle. I am in many Craft Breweries, and one of the significant issues with small breweries is Boiler Carryover, which is associated with improper boiler/steam systems installations. In most cases, space is an issue, so the boiler is too close to the major point of use, the kettle. When this is the case, the rapid demand for steam causes water to be pulled out of the boiler and mixed with the steam. Now you no longer have a steam boiler but a hot water boiler with a lower temperature affecting the boil. This event is not constant and usually happens with a change in steam demand. For instance, at kettle boil start, as steam jackets come on, or demand elsewhere in the production. I know from experience how vital wort boil and evaporation rates are, so an interpretation of the thermal process will cause problems. I use the example of trying to bake a cake in an oven that goes off and on. I wonder if a steam carryover contributes to your stratification issue, but it is possible.

If you need to learn about Boiler Carryover and proper steam distribution, several sites online explain the cause.

Cheers
Jerry Alvey
Senior Technical Consultant
Clarity Water Technologies
jalvey@claritywatertech.com
859-750-7817

Hi Cody,

Assuming your Kettle Boil is sufficiently robust, I doubt you have a stratification issue.

I suspect your hand-held refractometer is the issue.

The sample volume is so small that even a small cross contamination from the previous sample or sample evaporation on the prism can throw off your reading.

Make sure that you rinse the entire sample surface including the cover plate with fresh water. Then, using a soft tissue, wipe off all surfaces until completely dry before next sample.

Then, the sample itself can be problematic. You are pulling a boiling wort that will continue to evaporate and thus concentrate in the refractometer. So, you either need to let the wort cool a bit before placing drop in device or be very fast AND CONSISTENT when placing drop, closing cover and reading. A deviation in this time will affect evaporation and thus your reading.

Cheers,

Daniel Carey

New Glarus Brewing Company

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Daniel Carey
Brewmaster
New Glarus Brewing Company
New Glarus WI
(608) 527-5850
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