Date: Fri, 12 Dec 1997 23:06:09 +1100
From: "Andy Walsh" <awalsh@crl.com.au>
Subject: clini-to-rest
I just had to stick my pointy little head into Clinitest.
I felt what was missing in this debate was some actual data. The question is - can Clinitest accurately measure the wort sugars, or just glucose, which is what it is supposedly calibrated for?
The wort sugars are generally fermented in the following order-
glucose, fructose and sucrose
maltose
maltotriose
Some super-attenuating strains also ferment a little maltotetraose. Maltotriose is really a key sugar to monitor for fermentation, since most strains do not completely ferment it out. It is also the last to be fermented. Any decent fermentation monitor should be sensitive to maltotriose.
Although yeast generally ferments in the above order, this is not strictly true. Maltose will not be fermented only after *all* glucose is gone. Some yeasts will not glucose repress maltose and will ferment maltose right away. Some may not ferment 100% of glucose, or maltose. It all depends on the strain, the original wort composition and the fermentation conditions. ie. At the end of fermentation we would generally expect beer to contain mainly dextrins, maltotriose, maltose, fructose and glucose (approximate decreasing order), but it may contain any or all of these to some extent. You just don't know.
The Clinitest is based on the reaction of copper sulphate with a reducing sugar. Pretty much all of wort carbohydrates are reducing sugars, since they all contain glucose units at the end of the polymer chain. (Fructose doesn't, but is still a reducing sugar. Sucrose isn't a reducing sugar, but is *rapidly* converted by invertase to fructose and glucose, which are reducing sugars). The thing is, that the extent of the reaction decreases with the length of the polymer chain.
I tested Clinitest with 1% by weight of each of the following-
glucose (ACS grade - Sigma Aldrich)
glucose (homebrewing grade)
fructose (Select Foods - healthfood shop)
maltose (90% - balance is glucose and maltotriose - Sigma Aldrich)
maltotriose (95% - Sigma Aldrich)
maltodextrin powder (homebrew shop - known as corn syrup in Australia)
malt extract (Coopers)
The accuracy to 1% would be well within 5% of that for all except the last. I used a 0.01g accurate scale to measure weights (usually ~0.8g in 80g total to give 1%). The last I just diluted a 1.032 wort, as measured by hydrometer. I also measured sugar level as measured by Diastix glucose reagent strips, which are specific to glucose only. I would have liked to include maltotetraose but it cost too much! (I was extremely careful with dissolving/mixing, and prerinsing equipment first with the solution to be measured before measuring. All reagents were freshly opened. ie. no water)
I would first like to say I found the colour interpretation difficult. Even when using 1% ACS glucose I thought the mixture colour was a bit different from 1% on the chart. Also, one must measure exactly 15 seconds after boiling stops. Colour changes after this should be disregarded. Here are the results -
sugar Clinitest Diastix glucose ******* ********** ***************** ACS glucose 1% 1% homebrew glucose 1% 1% healthfood fructose 0.75-1% 0 90% maltose 0.5 - 0.75% 0 95% maltotriose 0.25% 0 maltodextrin 0.25% 0.1% malt extract 0.5 - 0.75% 0.1%
Clinitest reads low for the major sugars left after fermentation. Maltotriose typically forms 10% of wort gravity in an all malt wort. eg. 1.050 wort has ~5 SG points of maltotriose.The lowest measure on Clinitest is 0.25%, corresponding to about 4SG points of maltotriose as being the minimum resolution for this sugar. One of the most common fermentation disorders is an inability to ferment this sugar. Clinitest will not normally detect this. In addition, as one does not know the final sugar composition, a reading on Clinitest of 0.25% could mean very different things since it does not measure the different sugars to the same degree of accuracy.
Conclusion - Clinitest does not give an accurate portrayal of final sugar concentrations. It may be useful as a general fermentation indicator, but I won't rush out to buy one. However, if you want a glucose monitor, Diastix are great! Anybody know how to measure maltotriose?
Clinitest - courtesy of Calvin Perilloux homebrew sugars - courtesy Regan Pallandi of Eastern Suburbs Brewmaker also Sigma Aldrich (I paid for these! OUCH!) note- I am not defending hydrometers here either
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Another note on George Fix's recent post on sugar conversion during a step mash. Apart from the rapid conversion at or below 60C (as I commented on before), I would suggest the initial jump at 40C is due mainly to soluble carbohydrates already present in grain. The amylase enzymes are active during the germination and malting process (particularly beta amylase) and convert some of the starch into sugars during this period. This is significant and is why malted barley tastes sweet (forget the silly conversion in the mouth theory!).
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In the interests of accuracy I would suggest people are a little more careful when stating where they come from in relation to each other. I found a great website so you can get it just right. See
Andy.
from Dave Draper's house, go
8583 miles (13814 km) (7459 nautical miles)
west-southwest (248.8 degrees) as the crow flies
and there I am (or maybe that's Calvin's place!)