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  • Testing PH

    THE PH METER


    The strength of both acids and bases is measured by a yardstick known as pH, which is defined as the "common logarithm of the reciprocal of the hydrogen ion concentration" (don't worry about that, it won't be on the final exam; this mathematical legerdemain is required in order to yield a usable numeric range. Otherwise the number would have so many zeros as to be virtually incomprehensible). The value of pH ranges from 1 (highly caustic acid) to 14 (highly caustic base). Water - being neutral - lies in the middle with a pH of 7.0. The total amount of acid can also be measured as a percentage of the total volume of the must or wine, usually expressed in grams per litre (g/L), which is equal to parts per thousand, the measure used in industry. Total acid in this article means total titratable acid, or fixed acid.

    We measure pH using a pH meter. These meters come in various configurations, but unless one is prepared to pay top dollar for a laboratory model, check at a Winemaking store or a scientific-supply firm for a vest-pocket styled model with digital readout. Typically, a red wine should show a pH of between 3.2 and 3.6, while a slightly lower value, representing a more acidic solution - between 3.0 and 3.2 - works well for whites.

    You will need to calibrate a pH meter before each use; this is typically done by immersing the electrode in two solutions of known pH, one at pH 7.0 and the other at pH 4.0, and adjusting the reading on the meter until it reads accurately starting with the pH 7.0 standard. These solutions are made using distilled water and capsules of reagent, usually available from the same source as the meter. Since the standard solutions are not stable over time, they should be recreated each time the meter is put into use, unless the previous occasion was within several days. In addition, the adjusting mechanism on some meters is flimsy, for example, a countersunk screw made of soft metal that deforms after several uses, so the meter can become impossible to calibrate.

    All pH meters should be stored with the electrode kept damp, preferably in a solution made for this purpose by the manufacturer. A reasonably-priced pH meter should be accurate to at least one decimal place, for example, able to distinguish 3.2 from 3.3. It doesn't need to be as good as proper lab equipment, but it should be perfectly adequate for us amateurs. Be careful to check the difference between accuracy and resolution, for example if the meter is accurate to +/=0.2 but displays resolution to 0.01 then the overall accuracy is 0.2

    For rough measurements of pH, litmus paper is an alternative. This is a chemically-treated paper strip which changes colour when dipped in a wine, with the colour being an indication of the pH. One simply dips the paper in the wine, waits for a few seconds, then compares the ensuing colour with that on a chart, provided with the container. Matching up the colour with one on the chart indicates the pH with a reasonable approximation - but not the same as a pH meter. (thought by many to be useless in fact as they are too inaccurate)

    It should be emphasised that litmus paper only gives approximate results, depending as it does on both the quality of the product and your own ability to discriminate slight differences in colour. However, as a fast means of determining changes in acidity during fermentation, and the direction in which the change is occurring, it is useful for a quick, rough-and-ready determination. For absolute accuracy, however, a pH meter is highly recommended when you are making the final determination.
    Last edited by lockwood1956; 18-04-2007, 08:57 PM. Reason: feedback from Ben Rotter
    N.G.W.B.J.
    Member of 5 Towns Wine and Beer Makers Society (Yorkshire's newest)
    Wine, mead and beer maker

  • #2
    pH is a fundamental element of the winemaking industry. pH strongly influences wine properties such as colour, oxidation, biological and chemical stability.

    pH measures the quantity of acids present, the strength of the acids, and the effects of minerals and other ingredients in the wine. Wine pH depends on three main factors: the total amount of acid present, the ratio of malic acid to tartaric acid, and the amount of potassium present. Wines that contain little acid and excess potassium show high pH values. Wine with more tartaric acid, less malic acid, less potassium and more titratable acid has lower pH values.
    pH values range from 2.9 to 4.2 in wine. Wine’s chemical and biological stability are very dependent on pH value. Lower pH values are known to improve the stability, so winemakers usually prefer a pH range of 3.0 to 3.5. The wine is so stable in this range that many winemakers believe pH is a crucial guideline in wine making.
    There are many advantages to low pH values in wine. Low pH inhibits bacteria, causes sugar fermentation to progress more evenly and makes malolactic fermentation easier to control. Low pH also has a direct influence on the hot stability of wine. When bottled wines are stored in warm areas, protein precipitates out of them, causing serious problems. These wines are then treated with bentonite, which removes excess protein. pH is important to the treatment because bentonite successfully removes more protein when the pH value is low. If wine pH increases, bentonite is less effective, making it necessary to add larger amounts. The danger is adding too much bentonite because it can strip wines of their unique aromas and flavours.
    An example of the importance of low pH is displayed with Sauvignon Blanc. Sauvignon Blanc grapes normally have large amounts of protein, so they can be difficult to sufficiently stabilize when pH values are too high.
    Low wine pH results in better visual qualities as well. When pH is lower, both red and white wines maintain better colour intensity. Red wines have more and better colour and white wines do not brown as easily.
    When wine has high pH values, bacteria grow rapidly and undesirable bacterial fermentation is more problematic. This condition causes less biological and chemical stability, and poorer colour. Wines with a high pH always need more attention and greater care.

    Refer to the table below as to the effects of pH levels on wine quality:
    Attached Files
    Last edited by lockwood1956; 24-01-2007, 10:13 PM.
    N.G.W.B.J.
    Member of 5 Towns Wine and Beer Makers Society (Yorkshire's newest)
    Wine, mead and beer maker

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