The harvest season is here. We realize that this is the busiest and most critical period of the year for winemakers. Organizing the harvest and planning the work is vital to a successful and trouble-free vintage. Preparation for the analytical measurements relied upon to make winemaking decisions can sometimes be missed. To ensure success, it is important to prepare the equipment necessary to test pH, SO2, TA and Brix.
Here’s our Winemakers' Guide to making sure that you are ready for the season.
All buffers, solutions and reagents that open for more than six months should be replaced. Make sure that you have fresh product on hand. Calibrations and titrations performed are only as good as the buffers, solutions, and reagents being used.
Calibration buffers: Buffers, by definition, should resist change. But overtime, an opened bottle will degrade and the value on the bottle is not the actual value of the solution.
Hanna Tip: When measuring pH in wine, it is best to calibrate to two points. Most meters will allow for pH 7.01 and pH 4.01 calibration. Ideally the calibration should be done to pH 7.01 and pH 3.00. This allows for calibration to bracket the expected value which for wine is less than pH 4. Some meters are pre-programmed or allow for a custom calibration point (i.e. pH 3.00).
A clean electrode is critical to both an accurate and stable pH reading. Any stains or coatings on the sensitive glass surface cause a shift in potential generated by the pH electrode in a solution. Clogging of the junction (barrier between the inside of the electrode and the sample) increases resistance and affects the junction potential. Any coatings on the glass or clogging of the junction will result in sluggish and erratic readings. Electrodes should be cleaned periodically.
Hanna Tip: Specially formulated cleaning solutions are available to remove stains and deposits from the electrode. These solutions are preferred over a general purpose cleaning solution since they are formulated for a specific purpose.
A storage solution is designed to keep the pH bulb hydrated and to maintain free flowing junction. The hydration of a pH electrode takes 3-4 hours to completely form. Without this layer, the pH calibration will drift over time. It is also important to maintain a free flowing junction. If the junction is allowed to dry out then the diffusion of the internal electrolyte through the junction will be impeded. Not only will the junction potential be affected but also the stability/response of the electrode. Properly stored electrodes exhibit higher accuracy and have a longer lifespan.
Hanna Tip: Never store a pH or ORP electrode in purified (deionized, distilled, reverse osmosis) water. Purified water increases the diffusion of reference electrolyte into the solution and causes water to move into the reference cell by osmosis. Both will change the composition of reference electrolyte. If the solution cannot be replaced then the probe will.
Hanna Tip: Storage solutions are formulated to minimize any concentration gradient between the internal reference and the sample but also prevent any organic growth.
For a refillable pH or ORP electrode, a refill solution or electrolyte, is available. It is important that adequate level be maintained in order to provided adequate amount of head pressure. A positive head pressure (refill cap removed) allows for the flow of electrolyte through the junction into the sample. This is important since the ions in the electrolyte electrically connect the meter and electrode with the wine sample being tested. Levels of electrolyte should regularly be checked.
Hanna Tip: Single junction pH and ORP electrodes will use a potassium chloride (KCl) solution saturated with silver chloride (AgCl) while double junction electrodes use only KCl. The diagram below that will help identify what type of electrode that you have.
Having fresh solutions is essential but it is equally important that the electrodes be checked for functionality.
pH / TA / Formal Number (Nitrogen) determinations all use a pH electrode. The following is a quick way to determine the overall condition of a pH electrode. The overall condition is based on offset (pH7.01 mV value) and slope (difference between pH 7.01 mV and pH 4.01 mV). Both are of equal importance and any deviation from recommended values will result in erroneous readings of the sample.
SO2 potentiometric titrations use an ORP electrode for determining the equivalence endpoint. Even though the endpoint does not rely on a specific value to be reached (i.e. TA titration to pH 8.2) the mV response of an ORP electrode will provide an indication to its sensitivity in measuring a redox potential. It is important to periodically check the ORP electrode using an ORP test solution.
To check an ORP electrode the probe is placed in an ORP test solution of a known value. The HI7021L is a 500 ml bottle of 240 mV @ 25 ºC ORP test solution. A properly functioning electrode will read 240 mV +/- 20 mV. Readings outside this range indicate that the platinum tip/band needs to be polished or the electrolyte fill solution needs to be changed. If the ORP electrode cannot be brought within range then it should be replaced.
Hanna Tip: Very fine sand paper (i.e. 2000 grit) can be used to polish a tarnished ORP tip or band. The ORP sensing portion of the electrode should be shiny and not tarnished.
Hanna Instruments offers a variety of pH and ORP electrodes for various applications. What makes an electrode specific for any particular application is the design criteria required including body type, junction material, type of junction, fill solution, and for pH electrodes the type of sensitive glass used. For analytical measurements of wine juice and must it is important to have an electrode that resists clogging of the junction by the solids in the sample. The following are the pH and ORP electrodes recommended for pH/mV meters and titration systems:
The HI1048 series of electrodes are for wine juice and must. It is a glass body, double junction, refillable pH electrode. At the heart of the HI1048 is the unique outer junction made of PTFE.
CPS™ (Clogging Prevention System) is an innovation in electrode technology. Conventional pH electrodes use ceramic junctions that clog quickly when used in wine. When the junction is clogged, the electrode does not function. CPS™ technology utilizes the porousness of ground glass coupled with a PTFE sleeve to prevent clogging of the junction. The ground glass allows proper flow of the liquid, while the PTFE sleeve repels dirt. As a result, pH electrodes with CPS™ stay fresh up to 20 times longer than conventional electrodes.
A double junction electrode has an internal compartment surrounding the reference wire. Silver ions are present in the electrolyte of the internal compartment, which houses the Ag/AgCl reference wire; the electrolyte outside this compartment is silver free. The double junction design means that virtually no silver from the electrode enters the sample. This design allows measurement in applications where silver ions in the sample are undesirable or silver precipitates on the junction are likely to form.
The HI1048 is a refillable probe. Since it is a double junction pH electrode the fill solution is the HI7082 3.5M KCl. This solution does not contain any silver as with single junction electrode. The absence of silver will prevent any silver precipitate from forming at the junction surface and clogging it. Clogging of the junction will result in drifty and erratic readings.
The HI1048 electrodes are available with a variety of connectors based on the meter being used.
This connector is universal and can be used with any meter that has a BNC connector. It is the original probe supplied with the HI84102 and HI 84502 acidity mini titrator. It was also supplied with the HI9126V portable pH/mV meter.
This probe is the same as the HI1048B but has a pin connector used to enable the calibration check feature of the HI222W and HI2222W benchtop pH/mV meters.
This connector is proprietary for the HI99111 portable pH/Temperature meter. The HI1048D has a built in temperature sensor for temperature compensated measurements.
Much like a pH electrode, ORP electrodes also have their own design criteria. Since the ORP electrode is used with the same type of samples in wine testing as a pH electrode, the favorable criteria are similar.
The HI3148 is a double junction, refillable ORP electrode with a platinum ring for a sensor. The HI1048 also has the CPS™ (Clogging Prevention System) technology with the same unique outer junction made of PTFE as the HI1048 pH electrode.
The HI3148B has a BNC connector and can be used with any titrator that has a BNC input. The HI3148B is supplied with the HI84500 free and total sulfur dioxide titrator. It was also supplied with the HI84100 mini titrator.
Click the part number below for a complete list of titrants, reagents and replacement parts for Hanna Instruments wine specific titration system.
HI84500 – Piston driven syringe Free and Total SO2 Mini Titrator
Download quick guide for HI84500
HI84502 – Piston driven syringe TA Mini Titrator
Download quick guide for HI84502
Follow manufacturer recommendations for calibration and maintenance.
A well designed refractometer needs very little maintenance. If you are using a mechanical refractometer then you may want to consider upgrading to a digital refractometer for improved accuracy and ease-of-use.
The HI96811 and HI96813 wine specific digital refractometers are manufactured by Hanna.
HI96811 measures from 0 to 50% Brix with an accuracy of +/- 0.2% Brix.
HI96813 is the same as the HI96811 but also has an algorithm to predict the potential alcohol from the refractive index of the sample. The potential alcohol range is 0 to 25% V/V.
Both meters convert the refractive index of a wine, juice or must sample to % Brix. This conversion is based on the tables found in the ICUMSA Methods Book (International Commission for Uniform Methods of Sugar Analysis) that documents the changes in refractive index with temperature for a percent by weight sucrose solution. Since the majority of sugar in grape juice and must is fructose and glucose instead of sucrose, the reading is sometimes referred to as “Apparent Brix”. Common features for both meters are::
All the best for a successful harvest!