Editing Brix (section)

==Brix and actual dissolved solids content==
When a sugar solution is measured by [[refractometer]] or density meter, the °Bx or °P value obtained by entry into the appropriate table only represents the amount of dry solids dissolved in the sample if the dry solids are exclusively sucrose. This is seldom the case. Grape juice ([[must]]), for example, contains little sucrose but does contain glucose, fructose, acids, and other substances. In such cases, the °Bx value clearly cannot be equated with the sucrose content, but it may represent a good approximation to the total sugar content. For example, an 11.0% by mass D-Glucose ("grape sugar") solution measured 10.9 °Bx using a hand held instrument.{{citation needed|date=September 2014}} For these reasons, the sugar content of a solution obtained by use of refractometry with the ICUMSA table is often reported as "Refractometric Dry Substance" (RDS),<ref>"ICUMSA Methods Book, op. cit. Method GS4/3/8-13 (2009) "The Determination of Refractometric Dry Substance (RDS %) of Molasses – Accepted and Very Pure Syrups (Liquid Sugars), Thick Juice and Run-off Syrups – Official"</ref> which could be thought of as an equivalent sucrose content. Where it is desirable to know the actual dry solids content, empirical correction formulas can be developed based on calibrations with solutions similar to those being tested. For example, in sugar refining, dissolved solids can be accurately estimated from refractive index measurement corrected by an optical rotation (polarization) measurement.<ref>{{cite journal |last1=Sgualdino |first1=G. |last2=Vaccari |first2=G. |last3=Mantovani |first3=G. |title=Conversion of refractometric dry substance into real dry substance for quentin molasses [Sugar syrups] |journal=Journal of the American Society of Sugar Beet Technologists  |date=1982 |url=https://bsdf-assbt.org/jsbr/volume-21-1981/jsbrvol21no4p395to401conversionofrefractometricdrysubstanceintorealdrysubstanceforquentinmolasses/ |language=English |issn=0003-1216 |access-date=2022-07-20 |archive-date=2022-07-20 |archive-url=https://web.archive.org/web/20220720054741/https://bsdf-assbt.org/jsbr/volume-21-1981/jsbrvol21no4p395to401conversionofrefractometricdrysubstanceintorealdrysubstanceforquentinmolasses/ |url-status=live }}</ref>

Alcohol has a higher refractive index (1.361) than water (1.333). As a consequence, a refractometer measurement made on a sugar solution once fermentation has begun results in a reading substantially higher than the actual solids content. Thus, an operator must be certain that the sample they are testing has not begun to ferment. (If fermentation has indeed started, a correction can be made by estimating alcohol concentration from the original, pre-fermentation reading, termed "OG" by homebrewers.)<ref>{{cite web |title=Using your Refractometer Correctly for Maximum Accuracy in Home Brewing - Brewer's Friend |url=https://www.brewersfriend.com/2013/04/24/using-your-refractometer-correctly-for-maximum-accuracy-in-home-brewing/ |website=Brewer's Friend |date=24 April 2013 |access-date=20 July 2022 |archive-date=20 July 2022 |archive-url=https://web.archive.org/web/20220720054942/https://www.brewersfriend.com/2013/04/24/using-your-refractometer-correctly-for-maximum-accuracy-in-home-brewing/ |url-status=live }}</ref> Brix or Plato measurements based on specific gravity are also affected by fermentation, but in the opposite direction; as ethanol is less dense than water, an ethanol/sugar/water solution gives a Brix or Plato reading that is artificially low.