Via Hydrometer. A first reading (OG) at the start of fermentation and a second reading (FG) at the end of fermentation then divide the difference by 7.36.
That's the alcohol produced, For example a Start reading of 1085 and an end reading of 1005 will give a difference of 80 and dividing this by 7.36 will give an alcohol content of 10.9% by volume.
Another method is to multiply by 131. For example a Start reading of 1085 and an end reading of 1005 will give a difference of 80 and multiplied by 131 will give an alcohol content of 10.48% by volume
A Third method is to multiply by 132.715. For example a Start reading of 1085 and an end reading of 1005 will give a difference of 80 and multiplied by 132.715. will give an alcohol content of 10.62% by volume
For beer, wine, cider, Ginger Beer, Water Kefir and other Lacto-Ferments
Testing the alcohol level, and the potential alcohol levels ofGinger Beer, Japanese Water Crystals, Water Kefir can be done with a Hydrometer. These ferments although principally bacteria most often have yeasts contributing. A 3-4 day or longer ferment may produce 4-5% alcohol comparable to beer. As testified in a German drunk driving case.
Hydrometers are not accurate by themselves for alcohol readings of Kombucha Mushroom Tea, The margin of error of a Hydrometer is close to the alcohol level of these ferments which range from 1/2 of 1% to maybe 2 or 3% The acetobacter are busy converting the alcohol to acetic and other beneficial acids. The exchange rate of alcohol to acetic acid is basically 1:1. Therefore it is important to understand that the potential alcohol will produce the potential beneficial acids. You may get closer with these readings if you also calculate the Total Acids (TA) of the ferment and then subtract. But testing alcohol levels < 1% are difficult.
However if you bottle your Kombucha and/or do a Second Ferment and want to see if your alcohol is greater than 1% then the Hydrometer may be useful. Bottling and doing a second ferment most often do increase the alcohol percentage. As Lucy Lohan unfortunately discovered a few years back.
We can use starting SG (Starting Gravity) and the ending FG (final gravity) to determine if there are any fermentable sugars left or if we have a "stuck ferment". Important indicators for calories watchers, diabetics, sweetness / dryness of the brew and for bottling considerations.
The Hydrometer and the pH meter are two of the most important tools for judging and determining fermentation of our bacteria / yeasts ferments. These also allow us to correct mistakes and make course corrections and to talk to other brewers who may be experiencing similar brewing problems.
A Refractor Meter which reads in BRIX is another instrument that measures sugar levels. Typically used for wine and fruit. Easier to use, especially outside.
For Total Acids (TA)
Acid Test Kit - Titration Method is the simplest home method of testing for acids.
Acids produced during the ferment affect the balance of your brew. For example acetic acid has the sharp vinegar taste. While no one really enjoys drinking a bottle of vinegar, acetic acid is healthy and beneficial. For those wishing lowest-alcohol levels, acetic acid is produced by the acteobacter species of bacteria which are busy converting alcohol to acetic acid (wine to vinegar). In a sense the more acetic acid the less alcohol. You can actually have enjoyable high levels of acetic acid when balanced with Gluconic ACid (produced by the acetobacter strain : gluconobacter. Lactic Acid, produced by lactobacillus species of bacteria produce the more pleasant sourness and also balances the acetic acid.
You can taste the level of acetic acid (vinegar). You can also do a simple home test for Lactic Acid (two different test one for L-Lactic Acid and one for D-Lactic acid). Those tests are usually for wines, who do not want to sour their wines. Beer, Kombucha, and Lacto-ferments usually appreciate the sourness, and a swe said lactic acid balances out the harshness of the acetic acid. There is no home testing for gluconic acid and it is difficult to taste. Therefore a Total ACid test (TA) which reads typically as Tannic acid is a very reasonable guide to the acidity of your brew. You can add adjustments to raise or lower the TA.
pH is the Potential Hydrogen of whatever it is you are testing.A pH of 7 is neutral. Below 7 is acid and above alkaline. FDA and safety reasons food and drink ferments should have a pH below 4.6. Below 4.0 as read by a pH meter, which is far more accurate than paper pH is our recommendation. Yeasts, bacteria, molds and pathogens all do better or worse depending upon the pH. It is another tool to see how well your ferment is doing and if any corrections are necessary. Just because the pH is below 7.0 (acid) does not tell you your total acids. For example Braggs Apple Cider Vinegar has a pH of ~ 3, with 5% acidity. While Kombucha Tea a pH of ~ 2.5 and only a 3% acidity (Cornell University Study)
Another advantage of a Acid Test Kit is in helping to determine the alcohol level of your Kombucha Tea.
1. First determine your final reading of your ferment. Using a Hydrometer or Brix as stated above.
2. Then subtract your TA.
3. The remaining value can be predicted to be remaining alcohol.
Why do all this?
Remember these are only best estimates as almost any test <1% is subject to a margin of error typically greater than 1/2%. However the critical factor here is in determining your brewing parameters. These tests (sugar, alcohol, acids) along with your pH readings and Temperature records will give you a great record of where your ferment has been, is, and will be. Predictability and Consistency is value. These markers also provide a framework where home brewers across different brews can help and offer advice, where otherwise you're left to toss it out and repeat disaster after disaster.
For Personal Health
urine specific gravity
We also have included some information on determining sugar levels which is of interest to many of us, even though we are not diabetic. The hydrometer may test one's own urine, which may indicate dehydration or improper water metabolism. The hydrometer was not made for these purposes and therefore should not be concluded as a accurate test but as a relative means to judge where your kombucha ferment (or yourself) are.
Kombucha Modified Technique for Diabetics
to test their kombucha sugar content
the alcohol must be removed first by boiling,
Measure off 200 ml
Boil it until there is 100 ml left.
Add water to revert to the original volume.
Cool to room temperature,
Read the hydrometer
Multiply by 2 (the reading)
For example, if the hydrometer reads 1003 degrees, then the residual sugar will be 6 grams of sugar per liter, (1003 - 1000 x 2).
sugar converts almost one for one into alcohol, so a 5% sugar solution will yield roughly a 5% alcohol. The alcohol converts almost one to one into acetic and gluconic and other acids (leaving about 1/2 of 1 % residual alcohol. The highest alcohol reading for kombucha is really low compared to beer and wine. That is usually within the first 3 days. Thereafter it steadily drops typically ends with 1/2 of 1 %. A longer than typical ferment may result in all the sucrose (sugar) except for a small percentage of fructose and unfermentable sugars such as pentose. Typical expectations would be about 3-4 grams per liter. Every batch would be different.
The hydrometer may also read one's urine and be a early indicator of a disorder. This of course, is not FDA approved
Specific Gravity Urine: The specific gravity test permits the determination of urine specific gravity between 1.000 and 1.030. In general, it correlates within 0.005 with values obtained with the refractive index method. For increased accuracy, 0.005 maybe added to readings from urine with pHequal to or greater than 6.5. Elevated specific gravity readings may be obtained in the presence of moderate quantities (1ÛÔ7.5 g/L) of protein. The specific gravity of urine is a measurement of the density of urine; the relative proportions of dissolved solids in relationship to the total volume of the specimen. It reflects how concentrated or diluted a sample may be. Water has a specific gravity of 1.000. Urine will always have a value greater than 1.000 depending upon the amount of dissolved substances (salts, minerals, etc.) that may be present. Very dilute urine has a low specific gravity value and very concentrated urine has a high value. Specific gravity measures the ability of the kidneys to concentrate or dilute urine depending on fluctuating conditions. Normal range 1.005 - 1.030, average range 1.010 - 1.025. Low specific gravity is associated with conditions like diabetes insipidus, excessive water intake, diuretic use or chronic renal failure.