Jim's Beer Kit

Determination of alkalinity using CRS and methyl orange indicator

This is a procedure for the determination of the alkalinity of brewing liquor. Once determined a calculation is given for the reduction of the alkalinity to a predetermined quantity.

Equipment and reagents required

• 10ml syringe (usually found in the home as part of an ink jet refill)
• 1 litre bottle of distilled or deionised water
• digital scales preferably readable to 2g
• Carbonate Reducing Solution (also known as AMS)
• methyl orange indicator 0.04% (see note 5 at end)
• suitable glass container for carrying out determination (pint glass, pyrex jug etc)
• stirring implement (tea spoon)

Preparation of dilute acid solution

Place the bottle of distilled water on the scales and note the weight in grams (W1). Subtract 25 from this figure (W1 - 25 = W2). Pour off about 50ml into a clean glass and then carefully pour some of it back until the scales read the value of W2. CRS is a fairly strong acid so the use of gloves, appropriate clothing and eye protection are advisable for the following part. Using a clean dry 10ml syringe carefully draw up CRS solution to about the 5ml mark. Invert the syringe and hold a piece of kitchen towel over the exit, push the plunger in until all of the air is expelled. Now draw CRS solution into the syringe to the 10ml mark. Exhaust the contents of the syringe into the distilled water and repeat with another 10ml lot and a 5 ml lot so that 25ml of CRS have been added in total. Cap the bottle, mix well and label the bottle as CRS diluted 1/40 together with the date of preparation.

Flush the syringe well with plenty of tap water and then either flush several times with distilled water or take the syringe apart and dry with kitchen towel. Leaving the syringe to dry with traces of water that has high alkalinity will affect the final result.

Every 1ml of this dilute solution will neutralise 4.5mg of calcium carbonate.

Determination of alkalinity

Place the suitable glass container on the scales and tare. Add an appropriate amount of brewing liquor to the container and record the weight.

(The quantity to take should be such that it will require less than one 10ml syringe full of dilute CRS to neutralise the alkalinity and this would generally be: anywhere in the chalky regions about 125 to 175g, everywhere else about 250g.)

Using a clean dry 10ml syringe carefully draw up diluted CRS solution to about the 5ml mark. Invert the syringe and hold a piece of kitchen towel over the exit, push the plunger in until all of the air is expelled. Now draw CRS solution into the syringe to the 10ml mark.

Place glass container with the liquor in on a piece of white paper, add about 6 drops of methyl orange and stir. The colour should be pale yellow.

Now add the dilute CRS from the syringe to the liquor in approximately 1/2 ml aliquots and stir. If at anytime the colour from the indicator begins to fade (action of hypochlorous acid on the indicator) add a couple more drops. Continue adding dilute CRS and stirring until the colour just takes on a faint red tinge. This is the end point and the value on the syringe should be recorded.

Additional dilute CRS will cause the colour to become more red.

The alkalinity may now be calculated as follows:

Alkalinity as CaCO3 (ppm) = 1000 x volume of dilute CRS x 4.5/weight of liquor taken

Volume of undiluted CRS to add to brewing liquor:

(alkalinity from above equation - required alkalinity) x volume of liquor to be treated/180

Example

• weight of water taken = 238g
• volume of dilute CRS = 7.6ml

Then alkalinity = 1000 x 7.6 x 4.5/238  = 144ppm as CaCO₃

• Required alkalinity = 30
• Quantity of liquor = 27 litres

Volume of CRS required = (144 - 30) x 27/180  = 17.1ml

ONCE this has been added and the liquor stirred well to ensure complete reaction carry out the procedure again to ensure that you have not over or under dosed the liquor.

Notes:

1. This procedure may also be used with screened methyl red which is the preferred indicator for this determination but is more difficult to get hold of in a stable form outside of a laboratory environment.

2. The figure 180 was determined on a sample of CRS where it was found that it is a mix of hydrochloric and sulphuric acids. For this sample they were present as 1.6 moles of hydrochloric acid and 1 mole of sulphuric. It is not known if these are kept in constant proportion but the acid strength should be constant. Feel free to use 183 instead of 180.

3. Whilst not strictly interchangeable you may substitute mg/litre for ppm. Parts per million is correct for the determination because the quantity of sample (liquor) was weighed out and the answer is in weight form (milligrams) so we get mg/kg not mg/L

4. All images courtesy of Scroogemonster

Thanks to Wallybrew for the text and and Scroogemonster for the pictures on this page.