Paper filter for use with refractometer

[Birrofilo]

Hallo,
I am new here and this is my first post, so I would like first to express my pleasure in being part of this very knowledgeable community.

And now let me come to the question: I have a stupid problem which I cannot solve.

Any time I take a measure of a beer sample with the refractometer I obtain swinging results: one moment is let's say 5,0 °B and ten seconds later it's 5,5 °B. That frustrates me. I attribute this to the yeast in suspension, which clouds the sample and makes the refractometer's work uncertain.

I do let all things involved (refractometer, sample) get to room temperature for a few hours, and I filter the sample with some paper towels, but I see that the result is not clear enough. I am looking for some paper filter which would give me a clear sample so that the refractometer gives me an unambiguous measure.

I understand yeast cells are in the 5-8 micron diameter range, and that a coffee filter is totally inadequate for the purpose, having a typical porosity of 20 microns. I am looking for some kind of paper filter (or cloth filter) with a porosity of 3-4 microns. I cannot manage to find any: when the porosity is declared it is typically around 10 microns, and sometimes I see descriptions such as "qualitative" paper filters, but with no declaration regarding the dimension of filtered particles.

I only need this for the refractometer. It's not important to me that the filtered liquid is drinkable etc. it's not beer for myself

Also, it is not important that the filter is fast, I can wait one hour or two before taking the measure, not problem. If the filter is made out of cloth, I would like something reusable.

What do you use to solve this problem? What would you suggest?

Thanks in advance

 

[eric19312]

ive never heard of needing to do this. I don't for my samples and really have no issue getting a decent reading off a visibly cloudy sample. What type of refractometer are you using? Can you link to it?

I have a cheap one I bought off Amazon. I use it for brew day measurements and for sampling during fermentation and it works fine. A very murky sample might not give me a super crisp line but it is easy enough to estimate the mid point of the fuzz and I go with that. I only consider post fermentation refractometer samples to be directional indicators of progress, if I care to know final gravity I get that with a final gravity hydrometer.

 

[Birrofilo]

ive never heard of needing to do this. I don't for my samples and really have no issue getting a decent reading off a visibly cloudy sample. What type of refractometer are you using? Can you link to it?

I have a Milwaukee MA871.
It's basically this: Milwaukee MA871 Digital Brix Refractometer
(my one is green, I bought it a few years ago, but I believe it is the same instrument).

As you see, being a digital refractometer, I cannot evaluate the reading by looking at a line in the visor, which can probably have less defined margins, but it is still readable. I can only read a numeric value, and that fluctuates, which is frustrating, hence the need of a way to clear the sample of any solid.

When I use it with sugar wash for distilling, which is coming out of my fermenter decently clear, the instrument has no doubts and always tell me the same value.

 

[eric19312]

interesting. id been thinking about getting one of those but can see that would be frustrating. how about cold crashing the sample in an ice bath and decanting?

edited to add ... or get a centrifuge?

 

[eric19312]

https://www.southernlabware.com/min...CrO94kP1fYhE3JcAc1wIS_tLqSuNs9wBoCBD0QAvD_BwE

 

[Spartan1979]

I have a similar refractometer. If I'm reading samples from the kettle, I cool them first, but even then my readings may change over the next minute as the refractometer and the sample reach the same temp.

If I use it to read fermenting wort, I often have an issue with getting consistent readings. I imagine it must have something to do with the alcohol in the wort. It's not really designed for that purpose. I'm only using those readings so I can decide if it's time to start my diacetyl rest (after plugging the numbers into a correction algorithm).

 

[jddevinn]

I use a coffee filter

 

[jddevinn]

I attribute this to the yeast in suspension

Refractometers will not give correct measurements post fermentation. A calculator can give an estimate, but is dependent on a beer specific constant.

 

[Birrofilo]

@eric19312

Wow, that centrifuge is interesting! If I find working paper filters I think I would prefer them, but this new toy might be exciting.

@all

Yes I know how to use a refractometer to evaluate density of a fermenting beer. It works extremely well, when the wort is clear. I use this calculator: Refractometer Calculator - Brewer's Friend but a ton of others exist. They are all quite reliable to up to 1, maybe rarely 2 density points (in relative density terms). I use the refractometer to check the progress of the fermentation and when I see that it is the time to bottle, and take a sample for the hydrometer, I see that the hydrometer reading coincides, or is 1 point off, from the hydrometer "adjusted and calculated" number.

@jddevinn

Do you use specific, or generic coffee filters? Do I have to look for specific numbers, grades, writings?
Do they solve this exact problem? I can easily find coffee filters even here in Italy (where almost nobody brews that kind of coffee, but they can be found easily on the internet).

 

[BrewnWKopperKat]

Refractometers will not give correct measurements post fermentation. A calculator can give an estimate, but is dependent on a beer specific constant.

One of the forum moderators over in /r/homebrewing is tracking this (link) (sorry, don't have a direct link to something more substantial). One the other hand, a couple of people over here in HBT have had great results with their refractometer(s) (for example: Refractometers and final gravity (link))

I suspect (but don't know how to "prove") that "best practices" for a refractometer may be brand (and maybe model) specific.

FWIW, I use my refractometer pre-frementation and a final gravity hydrometer post-fermentation & scale the batch size to account for the measurement losses.

 

[jddevinn]

Regular paper coffee filters. Take a couple oz sample and let it filter through, takes a minute or two. Try to get the temp the same, I'll pour some of the sample onto the refractometer, remove it and then add the actual sample to help with temp. I'm using a digital refractometer..

 

[bracconiere]

https://www.ebay.com/itm/1000mL-24-...496897?hash=item44575d1fc1:g:ORMAAOSwjdFeemEt
and :

https://www.ebay.com/itm/5um-Hydrop...934572?hash=item364fe977ac:g:F84AAOSwnyNdEFCs
(just tossing an idea out...)

 

[A1sportsdad]

I take my sample in a 10 ml graduated cylinder and let it sit for an hour or two so that enough of the top clears that I can draw a sample from that. Helps a lot with a cloudy sample.

 

[Birrofilo]

I will go for ordinary coffee filters, as they are reported as sufficiently useful for my purpose.

This was very instructive and made me learn some new toys I did not know.

Thanks to all.

 

[youngdh]

I use an optical refractometer (look thru the view Finder). Other than the occasional challenge of guesstimating a reading due to a fuzzy line (I had to guesstimate the meniscus line on my glass hydrometer too) I’ve found it to be in agreement with my glass hydrometer reading at end of fermentation. I use the calculator at brewersfriend.com to adjust for alcohol and I always check calibration before a reading. I no longer double check using glass hydrometer as I trust my refractometer now and it’s so much faster to get a reading with limited waste of beer. If your refractometer adjust for temp, there’s no need to wait a long time for a sample to cool. By the time you’ve transferred a couple of drops with a sampling pippet and get the eye piece to your eye, the sample is at or near room temp.

 

[cheesebach]

I have the same Milwaukee refractometer as the OP, and while I've only used it for 2 batches so far, I have noticed similar difficulty in getting a stable reading when the sample has been cloudy. I think I'll try running it through my aeropress with a paper filter the next time and hopefully that will filter well enough to resolve the issue.

 

[moorejl57]

The coffee world uses refractometers and syringe filters to measure extraction. The filters are very expensive in my mind, but you can take a look at: VSTAPPS STORE — Syringe Filters for Espresso / Coffee

I have an optical refractometer, the VEE GEE BTX-1 and with it I can take a reading within a minute. It has a lot of thermal mass and stabilizes the sample in seconds.

 

[micraftbeer]

I have the same Milwaukee refractometer. When I was first using it, I got wild swings from measurement to measurement. But I bought a little ultra fine mesh strainer to pass the sample through before measuring and that solved the problem for me. I tried coffee filters but that was just a mess, too slow.

My process is to let the sample cool a bit if hot, to get closer to room temperature. Then I use my sample syringe to stir the sample up good, then I drip it on the mesh strainer which filters out hop debris. I watch the temperature display to make sure temperature is stable and then push the button to get a reading.

I wipe the sample dish out with a paper towel and do it again. I sometimes will see the first measurement 0.1 brix different. If so, I do it a third time and get a consistent reading.

Same process for pre-boil, OG, and FG (of course using refractometer correction calculator of fermented wort via Brewfather).

But this works with cloudy worts or clearer worts.

 

[micraftbeer]

I guess I can add how I collect the FG sample, as maybe that could be contributing to your issue. I use a Tilt to monitor fermentation progress and know when the beer is finished. When transferring that finished beer from fermentor to cold crash keg, after a couple seconds of flow from the transfer pump into an empty bucket (to push out any air in my transfer lines), I pump about 4 oz into a cup. And I get my refractometer sample from that 4 oz sample.

If you're sampling from your fermentor while still in fermentation, I'm guessing you might get more variation.

 

[Birrofilo]

@micraftbeer

That's interesting. I wouldn't mind waiting for my FG measure because I wait hours in any case for temperature equalization, but I will soon make my first all grain beer, and I think using the refractometer for pre-boil and post-boil density measurement would certainly benefit from speed. If something is out of order, I can remedy on the spot.

What kind of mesh strainer for hop debris do you use? Is it tissue of metallic?

I have a hop basket with 300 microns porosity but i guess that would not be enough tight.

Can you point to the strainer that you use? Maybe a tissue strainer can be much more filtering.

I am surprised that yeast cells can actually pass through paper towels, but they do, so I had ruled out strainers. Maybe when they are hot they tend to "clump" together.

 

[micraftbeer]

It was a stainless steel mesh strainer. Attached are some pictures. I don't know the details of micron mesh, etc.

 

[day_trippr]

There's some humor here. One person is using coffee filters while another advocated a window screen

I'm still not getting the crux of the problem here. I brew some hella chunky beers and have not had any problems getting periodic status readings from a refract with fermenting wort. I've been checking a triple chocolate imperial stout over the last couple of weeks and the plot line is perfectly linear.

I'm wondering if the OP's erratic readings aren't due to a dodgy tool - maybe the prism is loose or something...

Cheers!

 

[Birrofilo]

@micraftbeer

That's a very normal tee or milk strainer, I suppose you use it on your hot wort and it will filter the hop debris. Yeast cells will certainly pass through it though.

@day_trippr

As I mentioned already earlier in this conversation, I have a digital refractometer and I see no "plot line", linear or not. The display of the instrument gives me directly a number (5.6 °B or 5.0 °B) and if the sample is not clear because of the yeast cells in suspension it will give me inconsistent readings a few seconds apart.

Today I will take some measurements on three fermentations and I will try a different procedure:

a) A microwave cloth (never tried that) as a filter. I have ordered the coffee filters online, but have still to receive them;

b) I want to try to put a minute layer of sample on the crystal. Normally I make a "small hill" of liquid on the crystal: I just drop the liquid on the crystal and the superficial tension makes the small hill, the drops will not spread themselves spontaneously. But, thinking about it, the normal kind of refractomer spreads the layer of the sample extremely thin, so I should try to do it myself on my digital refractomer, I will try to use just an extremely thin layer of sample. Maybe that's my mistake. I'll keep up updated.

 

[micraftbeer]

I can add in some feedback I had from Milwaukee, as I was working with the as I was doing my hands-on review of the MA871. I had a few discussions with them on the variation in gravity readings. Unfortunately, most of it was over the phone, so reliant on my memory. He mentioned two things to me to be aware of. One was particulate in the sample can throw off the reading, and the other was something about "letting the sugars settle" can give different readings.

He said that they'd get people complaining about variability when they'd take a sample, collect a reading, and then keep hitting the button to take a reading on the same sample, and seeing it change over time. He said this would give you variable readings because of the "sugars settling". It seemed odd, but whether this was the cause or not, they did not recommend taking multiple readings of the same sample sitting on the dish. They said if you want another reading, clean off the first sample, and get another one. I have found that a rapidly cooling sample can give unreliable readings, surely because they use temperature compensation as an input to their calculation of gravity readings.

On the subject of particulate matter, he said it was a problem. I was expressing how it being a problem, would be a problem for beer brewing because of hop debris. Below is a cut & paste from our email exchange on that specific topic. As I mentioned, I bought some paper disposable coffee filters and tried that once before bailing and buying that stainless fine mesh strainer.

• You mentioned that particulate in the sample can throw off readings. But you also mentioned while we were talking that if you let a sample sit too long, the sugars start to settle out. The pre-boil sample has no hops added so that one’s easy. But at the end of the boil, you need to take a gravity reading, at which point, there’s likely to be hop debris floating in the sample. I was letting it settle in a sample glass before siphoning some off to measure to avoid hop debris from skewing the measurement. But I was thinking of your comment about the sugars settling. Any recommendations for how to best deal with that?
  • Filter the sample through cheese cloth or coffee filter to remove particulate mater and then take a reading with the vol on the pan 1/3 to ½ full – if you feel it is necessary to retest then dump the sample, clean the lens of flush with distilled water and create an new sample using the same filtering process

 

[Birrofilo]

@micraftbeer

Very interesting, thanks. I see I was not the only person to have the problem of inconsistent readings. This reinforces my recent idea that the thin layer strategy might be the way to go. If the layer is very thin, as is the case with an analogic refractometer, there is no place where the sugar can "settle". The sugars "settle" because the sample is too high in height.

 

[micraftbeer]

Except note that he specifically said to have the sample bowl 1/3 to 1/2 full. Although it's still using "refractometer technology", I don't know if a thin layer would be a problem or not. But that should be super easy to try out, and then you'd know for sure.

 

[Birrofilo]

The "sample bowl" is probably, going by eyesight, 2 or 3 mm high. That means putting in the bowl a 1mm high sample or less. This is probably the right direction to go. Either a very thin "foil" as is the case with an analogic refractometer, or, if the instrument wants more height, keeping the sample very very thin in any case. We will know in a few hours.

 

[Vale71]

He said that they'd get people complaining about variability when they'd take a sample, collect a reading, and then keep hitting the button to take a reading on the same sample, and seeing it change over time. He said this would give you variable readings because of the "sugars settling".

That's complete poppycock. Sugars or any other fully dissolved solids won't "settle" even if you were to wait literally a thousand years. The guy you talked to was clearly totally incompetent, so I'm guessing either sales rep or customer care?

What can and does settle is particulate (yeast and whatnot) and that will cause spurious reflections that will interfere with the actual reading.

 

[Birrofilo]

I am testing the "thin layer" strategy. I cannot arrive at a definitive conclusion. The instrument appears to give fairly constant results (maximum deviation is 0,1 °B, but that's acceptable, because let's say an oscillation between 5,05 and 5,06, which is only 0,01 °B, would be rounded as 5,0 and 5,1). But then, if I let the sample sit for let's say 20 minutes, the measure change and I don't know whether to attribute this to some evaporation, some residual yeast settling down, or the adjustement of temperature, which I can observe in the digital thermometer provided by the instrument (from 19,1 °C to 18,9 for instance).

What I can say is that a thin layer of sample certainly constitutes an improvement. I put one or two drops and spread them over the cristal. The liquid reaches the metal edge and completely covers the crystal, but doesn't go higher than that.

I proceed now to filtering with the microfiber cloth... done. The wort goes through the microfiber very fast (as expected) and the result is visually not different from the unfiltered one.

The solution to the problem is probably coffee filters & thin layer.

At this final density, 0,1°B is more or less half a density point, not something to lose sleep for. If coffee filters narrow the variation to 0,1 °B, that's fine.

 

[jrgtr42]

I've had good results with my refractometer - it is an optical, though.
the first half-dozen batches I checked before and after as a backup with hydrometer, punching it in the brewers friend calculator. I found that my readings were spot on, except for one user error (code ID-10T,) so don't bother anymore backing up.
One thing i did notice is that it's harder to get a crisp line with flourescent lights compared to incandescent or LED.

 

[Birrofilo]

@jrgtr42

Actually one of the reasons why I bought a digital refractometer rather than an analogic one is that the digital refractometer has its own light source. An analogue refractometer is dependent on the light source you use. I had read that they are precise only with solar light. More probably, they can work well also with artificial light provided that the calibration is made in that light conditions.

If I had to buy a refractometer now I would buy an analogue one as I see that it is ultimately more practical.

 

[moorejl57]

I would imagine that evaporation plays a big role in a changing reading over time if you have a very thin layer. There are some fairly cheap non sterile syringe filters on amazon that you could try.

 

[Birrofilo]

I used the coffee paper filters yesterday for the first time, and I have to say that, after judicious waiting for temperature equalization, the sample gave readings within 0,1°B and actually agreeing with the hydrometer. I actually filtered the beer twice through the same filter, because it was decently fast.

I will go with the coffee filters until I consume them, which will take a lot. If I encounter problems down the road, I will examine more sophisticated solutions. For the moment, the humble and cheap paper coffee filter is OK. Thanks to all for the help and for having reconciled me with my refractometer (which is not humble and not cheap).