This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
A quantity of extract equal to 10 c.c. of the original beer may be taken, and the dextrin hydrolysed by boiling for four hours with 40 c.c. of normal sulphuric acid. After neutralising the acidity, the total reducing sugars are determined with Fehling's solution as before. Deducting the " apparent maltose," as above determined, the remainder is calculated to dextrin.
Otherwise, the optical rotatory power of the beer is determined. From the angular value is deducted the number of grams of maltose per 100 c.c. X 137. The remainder, divided by 2, gives the number of grams of dextrin in 100 c.c. of the beer.
The total nitrogen is estimated by Kjeldahl's process on 20 or 25 c.c. of the beer, evaporated to near dryness in the long-necked flask used for the digestion with sulphuric acid. Percentage of nitrogen x 6.25 = per cent. of proteids.
A convenient quantity - 10 to 20 c.c. according to the amount of solid matter in the extract - is diluted with water to 250 c.c, and the sugars are determined on 50 c.c. of the diluted liquid. The gravimetric Fehling process is generally adopted, and the results are expressed in terms of maltose.