Sooner or later, most serious winemakers conclude that it isn’t good enough to simply follow a recipe blindly. That’s a bit too much like painting-by-numbers. The expression of one’s own skill and artistry makes the difference between an ordinary wine and something uniquely personal. But to do that, it’s necessary to understand a bit about the composition of the wine. There’s an old saying that if you can’t measure it, it doesn’t exist. So it seems to be self-evident that – if we are serious winemakers – we should understand the measurements that add up to our favorite beverage.
If you want to analyze what is right, or wrong, about your wine, you need to do some science. This can be very simple, or a little complicated, or even ridiculous. For the amateur, there are a few options that help to avoid the extremes. This means we will not be trying to emulate a research lab, but rather use readily available equipment and simplified techniques to discover what we can do to improve our wine. Your home laboratory, which may be as simple as a corner of your winemaking bench, requires a few basics. In broad terms these are measuring equipment, cleaning agents, and records of results.
The Handy Hydrometer
The hydrometer is the first, and most indispensable, measuring instrument in your home lab. This is a simple device that measures the relative density – or “specific gravity,” usually contracted to “SG” – of a liquid. This figure is important for determining, first, how much sugar is contained in the juice (and therefore what the alcohol yield should be) and, finally, when fermentation has reached completion. The hydrometer consists of a thin sealed glass tube with graduated values marked on it, usually in the form of a strip of paper inside the tube, held in place with a spot of glue. The tube has a bulbous, weighted bottom. This makes it float upright, but partially submerged, in a liquid (in our case, wine must). The method is to place the hydrometer in a “testing jar,” which is actually a glass or plastic cylinder sealed at the bottom, containing the wine or must to be tested. Ideally, the liquid should be at 60° F when the reading is made. In rough terms, 0.001 should be subtracted from the reading for each 10° F (5° C) below 60° F (15° C), and 0.001 added for each 10° F above 60° F. Since the density of a liquid changes with temperature (density decreases as the temperature rises), the readings will be incorrect if the wine must is at a temperature different from that for which the hydrometer is calibrated. In this case, if the wine must is at 70° F (21° C), a reading of 1.085 actually means a value of 1.086. It should be noted that some hydrometers may be calibrated at a different temperature (for example, 68° F); before applying a correction factor, ensure that you know what the calibration temperature is (it should be marked on the hydrometer itself).
To obtain the reading, the hydrometer is floated (not dropped into) the liquid. It is important to handle the hydrometer with reasonable care, since it is somewhat fragile. The hydrometer is then given a couple of quick twists between the fingers to dislodge any bubbles (which would otherwise affect its buoyancy, again leading to inaccurate readings), and then viewed at the point where the stem breaks the surface of the liquid. The scale marked on the hydrometer will give the specific gravity. It should be noted that the liquid actually forms what is called a “meniscus” at the edges, where surface tension causes it to climb slightly above the level. The reading should be made at the point where the surface is penetrated, not at the higher level of the sides.
Many hydrometers on the market, especially professional ones, use a different scale, known as Brix (or Balling in Europe), which directly measures sugar content. While the concept is identical, the scale is different. Roughly speaking, 1 degree Brix is equivalent to .004 specific gravity points, so that a Brix of 0 equals 1.000 specific gravity, while a Brix of 24 degrees is equal to 1.100 specific gravity.
When a fermentation is started, the liquid will consist primarily of water, fruit solids (grape solids in the case of grape wine), and sugars. The specific gravity reading, which should be in the range of 1.075 to 1.090, will – with readily-available tables – tell you not only how much alcohol may be produced, but by measurement on a frequent basis, how the must is progressing to completion. By definition, water is the standard, and has a specific gravity of 1.000. That of pure ethyl alcohol is 0.792, so that a “dry” wine – one containing no sugar, just water, alcohol and some dissolved solids -will have a specific gravity of less than 1.000 (typically in the range of 0.990).
Over the course of the fermentation, readings drop, showing that sugar is being converted to alcohol. When the readings stabilize, and the total drop indicates that alcohol conversion is complete, the new wine is ready to be removed from the fruit and yeast debris it has thrown. A wine thief can be a helpful device for the home winemaker during fermentation, since it is wide enough to accommodate a hydrometer. It can be used to take samples as well as to take hydrometer readings while you ferment in a glass carboy. You can keep a thief-hydrometer in a carboy with sanitizer so you only need to rinse it off before using it.
A number of tables have been produced that attempt to relate initial sugar content to final alcohol level, but there is considerable disagreement between them. The reason for this is that some are based on a “laboratory situation” of a pure sucrose solution in water, whereas grape juice also includes “non-fermentable” substances that add to the specific gravity, but not to the alcohol content. Further, calculation of alcohol production depends on total drop in specific gravity during fermentation, not just on the starting specific gravity (a juice that ferments out to a final specific gravity of 1.010 will have a lower alcohol content than one which finishes at 0.992, if both started at the same specific gravity). Some tables take account of this by showing that a fermenting must at SG 1.000 actually still has some sugar present, while others do not take this into account and show no sugar content at this level. However, consistent use of the same table will allow you to achieve consistent results, which is more important than accuracy to three decimal places.
The Acid Test
An acid testing kit is the next most important item in your lab. Acids, as most people know, are chemicals which, in high concentrations, are caustic and damaging. Their chemical opposites are known as bases or alkalis (such as lye). These are also, paradoxically, caustic.
When acids are dissolved in water, their molecules dissociate – break apart – with hydrogen ions being released into the liquid (some acids release more hydrogen ions than others, and thus are more “active” than others; food acids are typically very weak). Chemically, hydrogen ions have the symbol H+. Bases, on the other hand, dissociate by releasing hydroxyl ions, with the chemical symbol OH-. If the two encounter each other, they neutralize each other, combining to form plain water, while releasing energy in the form of heat.
Virtually all fruit contains acid, but fruit acids are mild, and are found in relatively small concentrations.In juices acid gives a sharpness or zest to the flavor; pineapple juice, for example, is higher in acid – and sharper in flavor – than the juice of ripe apples. In a wine, too much acid makes the taste unpleasantly sharp, but too little leaves it bland and uninteresting.
We can measure acid in two ways; in titratable acidity, which measures the total amount of fixed acid present, regardless of its strength; and in pH, which measures the activity or strength of an acid, regardless of its concentration. Although our taste is more correlated with acid activity than with its concentration, the latter is easier to measure, and – if we are dealing with the normal acids one experiences in food and drink – reasonably accurate.
Your home lab should therefore contain an acid titration kit. This consists of one or two Titrets – a syringe without needle, but calibrated in cubic centimetres (CCs), also known as milliliters (mL) – plus a plastic or glass testing jar and two containers of reagent (that’s chem-speak for chemical solutions). One of these is sodium hydroxide, at a known strength of 1/5 normal (0.2N), and the other is phenolphthalein solution, which has the interesting property of being colorless in an acidic solution, but which turns red in an alkaline solution.
The process is simply to add a measured quantity of the sodium hydroxide to a measured quantity of the wine, which is acidic, and noting exactly when the color change occurs to indicate that all of the acid has been neutralized. This is a lot simpler than it seems and the process is as follows:
Using 15 mL of wine (to which 3 drops of phenolphthalein solution has been added) one adds, a small quantity at a time, a 0.2N sodium hydroxide solution (trust me; it works). The color change from white to pink indicates the neutralization of the acid. The magic formula is that the acid content of the wine, in grams per liter (or parts per thousand), exactly equals the number of mL of sodium hydroxide used; thus, 7.5 mL equals an acid content of 7.5 grams per liter, measured “as tartaric”. Acid titration kits are available virtually wherever winemaking supplies and ingredients are sold.
Do be sure, though, that you are measuring apples with apples; British books use “as sulfuric” by their standards, and the values obtained are only 2/3 our measure of “as tartaric” equivalent. Also, as a rule of thumb, the sodium hydroxide should be replaced every six to nine months, but the phenolphthalein will last a couple of years.
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 liter (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 3.4, 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 asolution made for this purpose by the manufacturer. A reasonably-priced pH meter should be accurate to 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.
For rough measurements of pH, litmus paper is an alternative. This is a chemically-treated paper strip which changes color when dipped in a wine, with the color being an indication of the pH. One simply dips the paper in the wine, waits for a few seconds, then compares the ensuing color with that on a chart, provided with the container. Matching up the color with one on the chart indicates the pH with a reasonable approximation – but not the same as a pH meter.
It should be emphasized 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 color. 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.
Many of the measurements you will make – such as specific gravity, but also starting conditions of your wine and ongoing ambient conditions during fermentation – are temperature-dependent. Two types of thermometers are advisable: the floating kind of thermometer, to measure temperatures in the must, and one other – which can be either a standard household one, or a liquid-crystal display – to indicate room conditions. Most supply stores sell thermometers, and if not, you can try a pet store or hardware store. Another option is strip thermometers, which can be stuck to a carboy or simply tacked to a shelf. They are readily available and give reasonably accurate results.
In the Balance
Balance scales are your next item of choice. My balance scale measures down to 1/10 gram. You can’t get much finer than that. Why do you need one? Because in small quantities of wine production, which is what most home winemakers are involved in, it is sometimes necessary to measure additives in gram quantities, and an accurate scale is a great tool to have at these times – for example, when determining the quantity of oak chips to add (in an oaked white wine, typically 3 grams per liter). Kitchen scales work well for larger quantities, such as sugar addition, where gram accuracy is not really important.
For volume measure, invest also in a measuring cup and, if available in your area, a graduated cylinder with liquid measure. There will be times when you want to add a few ounces of sugar and a measuring cup is more convenient than a scale. The graduated cylinder is handy when using recipes that require, for example, the setting aside of, say, 150 ml of “sweet reserve.”
Ordinary measuring spoons will also make life easier. For conversion purposes, one teaspoon equals 5 ml (or CCs), and one tablespoon equals 15 ml/CCs. These are useful when one is adding small quantities of additives such as sulfite, tannin and yeast nutrient. You can do your own math for table and teaspoons.
Ever wondered how much S02 you have in your wine? Try using, in your home lab, a set of sulfite Titrets. These consist of glass tubes containing a colorless liquid, to which you fit a thin plastic tube that is provided with the kit. The ampoule is then inserted into a plastic tool which snaps the thin glass wand at the end of the ampoule and then functions as a pump to draw a small quantity of the wine into the it. Initially the sample will turn blue, but after successive additions of the sample, the color changes back to colorless. The ampoules are marked with gradations from 10 to 100 miligrams per liter, and it is a simple matter to read the level from the engraved numbers. Titrets are available at home-winemaking stores or from CHEMetrics in Calverton, Virginia. (See “Solving the Sulfite Puzzle“, also found in the Winter 2000 edition of WineMaker).
Advanced and serious winemakers might consider chromatography. These identify the presence of even very small concentrations of a substance in a sample to be tested, by analyzing the characteristic (and unique) color “signature” they produce. Equally important, chromatography measures the approximate amount of the substance. The most accurate (and expensive) way of doing this is by gas chromatography, a method limited generally to large research laboratories or some university facilities. However, a simpler, and fairly easy to use, alternative is paper chromatography. A paper chromatography kit can be obtained from a scientific supply store, or one of the larger suppliers to home winemakers, with a current price reportedly under $40 US. Chromatography is a particularly useful science for determining the progress (and completion point) of malolactic fermentation, which is the technique of converting sharp-tasting malic acid into milder and more complex lactic acid through the use of a lactobacilli culture. It is frequently used in red wines and Chardonnays, which have a higher than desirable level of malic acid (which has a taste reminiscent of unripe apples, and mars the flavor profile of reds and Chards). The chromatography kit can be used to determine when the malic acid has been totally converted to lactic, since the malic “signature” will disappear and the lactic “signature” will appear instead.
The technique for using the chromatograph involves putting a small drop of wine on a blotter and then standing it up in about an inch of developer liquid, preferably in a large jar with a lid. After a duration of six hours, the blotter is taken out and developed. The results are determined by using the instructions that come with the kit. The home winemaker can probably test over 100 wines with this method before needing more developer solution, which costs about $10 US.
Keep It Clean
Sterilants are a primary ingredient of your lab. A fermenting wine must provides an environment particularly suited to the growth of fungi and bacteria which, if unchecked, can spoil the wine. Dirty or contaminated equipment, or surroundings, can infect the wine either directly (in the case of equipment) or indirectly by providing a medium in which spoilage organisms can proliferate.
Sterilants come in a variety of types, each of which is specific to a particular function. Some include a detergent to assist in removing foreign matter. Examples of these are the commercial products Sanitone and Chloriclean. (Chloriclean is widely available in winemaker supply stores, but you might also want to check with your local dairy supplier for a bulk purchase; farmer co-ops also often have sterilants that those of us in the suburbs don’t know about.) When used on equipment or containers that will come in contact with the wine, these must first be thoroughly rinsed away so that no noticeable trace of the detergent remains.
Chlorine-based sterilants, such as Clorox and similar products, sterilize by bleaching the offending matter or stain. This process of denaturing destroys the integrity of the material, which can then be readily rinsed away. Chlorine bleaches are particularly useful for removing stains from bottles or carboys, or cleaning up after a spill in the winery. However, they can cause irritation of the nasal passages or eyes in a confined space and, when used on equipment with which the wine will come into contact, must also be thoroughly rinsed away.
Note: Chlorine bleaches should not be used on stainless-steel items because they will corrode the metal. Second-hand barrels, which are generally not a good idea (see “Wooden it be Lovely“, also found in the Fall 2000 issue of WineMaker) require different treatment if you are determined to use them. Older books suggest a combination of soda ash and household lye; others suggest washing soda at the rate of 1 pound per 3 gallons of hot water, as a means of removing scale from inside the barrel. Again it is crucial that these should be thoroughly rinsed out before using the cask.
Sulfur-based sterilants are used to destroy bacteria and fungi only, and do not convey any significant cleansing action. The old technique for keeping a clean barrel “sweet” was to burn a sulfur stick below the bung-hole of a barrel placed upside-down on its cradle; alternatively, a metal “spoon” fixed to a long handle, in an L-shaped form, was filled with powdered sulfur, set alight, and lowered into the barrel. This released a strong concentration of S02 fumes which destroyed any bacteria present.
The current sanitation method of choice for most winemaking equipment, including clean barrels, is a concentrated solution of potassium (or sodium) metabisulfite. I use one teaspoon in six U.S. gallons of water, which gives a concentration of 100 parts per million (ppm) of SO2. Other winemakers may prefer higher concentrations. When using higher concentrations, you might want to rinse your equipment with water before using it. If you use a lower concentration – say, a half-teaspoon of metabisulfite in six gallons of water, which equates to about 50 ppm – you can simply drain the equipment. The small amount that may be left after draining a sanitized wine bottle, for example, is unnoticeable and provides a measure of protection while the bottle is being filled.
Keeping a record of your results is an important, yet often overlooked, aspect of winemaking. In addition to making a list of ingredients – including source and cost of each ingredient – it’s a good idea to note the amount of acid, tannin and nutrient added, and the yeast variety used. You should also record the starting specific gravity and acid readings, the date fermentation began, any observations as fermentation progresses, dates of each racking, any additions during fermentation (such as sugar, sulfite, stabilizer and sweet reserve), fining agents or filtering, and any temperature corrections.
Depending on your expectations or level of motivation, your records may be as elaborate as a computer database or a commercially-produced log book, or as simple as a card index. (Also see the downloadable log chart here at the website.) Having tried all three versions, I prefer the latter. A book of tasting results, which can be used both for your own wine and commercially-produced wine, will also bring back fond memories of the superior wines you have encountered, and, of course, enhance your bragging rights.
The Nose Knows
The most important instrument you can employ is your nose. Sadly, we often fail to use the best instrument we possess … our own senses!