Winemaking Notes......acid, pH and malolactic fermentation
These notes are directed at red wine making. It is possible to make a wonderful wine without knowing anything about these issues. However, as in any complex science, it is easier to appreciate and trouble shoot with knowledge. I'm just giving you a bit of information to work with. As always, keep your equipment clean, protect your finished wine from air and extreme temperatures, make sure the wine ferments dry and taste often.
Tartaric and malic acids comprise 95% of the total acids present in the grape... As the sugars increase, the acid drops and the pH rises
What does acid do? It affects the color ,flavor, balance, body, aging ability, the microbial stability and oxidation. With the high sugars we deal with these days, it isn 't unusual to have juice with acid of .4gm/100ml (%) or less and a pH of 3.8 and above. Most commercially made red wines have acids around .6gm/100ml and pH less than 3.8
Why adjust acid? Although wine doesn't harbor human pathogens...it can grow bacteria and yeasts that make your wine smell and taste bad if conditions are right. Being "right", I mean any or all of the following: too warm, acid too low, pH too high, too much air contact, left on lees too long and dirty equipment . We'll talk about bad wine later under" problems".
Acid drops out of your wine in the form of tartrate crystals during its lifetime...so wineries constantly monitor acid and make additions(almost always tartaric) as necessary.
Home winemakers can add purchased dry tartaric acid or add some second crop or blend with a high acid juice/wine to raise the acid.
Trying an addition in a small amount of wine prior to the actually addition is a good idea. California red wines seldom need to have acid lowered but that can be done too by the addition of calcium carbonate or by putting it through malolactic fermentation. High acid reds are found in cool growing regions.
As you know pH is tied to the acid of your juice/wine and ranges in wine from 2.9 to 4.0. PH can be lowered by the addition of TARTARIC acid. A high pH wine is more susceptible to microbial growth and it takes more SO2 to protect it... which leads us to the next topic...
Red wines can go through a second fermentation where bacteria(not yeasts) convert malic acid to lactic acid. It is fairly common practice for commercial wineries to inoculate their red wines and some whites with strains of this bacteria (just like with yeasts some strains of the bacteria improve the wine others cause off characters). Why do this????????
Malolactic bacteria like warm temperatures, low alcohol, low acid, low sulfur,high pH and lees....During the ml fermentation, CO2 is formed (gassy)and the wine develops a spoiled milk/sauerkraut smell. YO WINEMAKER! do you want this to happen to your prize wine IN THE BOTTLE?
So... how do you prevent it????? Well maybe you can't. so if you can't beat it, try to join it.
If you have your wine in an oak barrel that had wine in it that had gone through ml fermentation.... it will go through on its own! If not you can buy a freeze dried culture and you can inoculate at the latter part of yeast fermentation (or after) while the wine meets the above criteria. DO NOT ADD sulfur or acid or clean up your wine too much if you plan to put it through ml.. If it doesn't finish in two weeks.. give up...clean up the wine and .it will finish next spring!
SO.......... How do you know it's finished (or even started)? In the commercial wineries, ml progress is monitored by paper chromatography.
If you put a paper towel on its edge in water, you will see the water gradually move up the paper towel. In chromatography, the" water" is a fluid (solvent) that dissolves different acids and as it "wicks" up the special chromatography paper, each of the acids has a spot where it gets "stuck". After an overnight stay in the solvent, the paper is dried and each acid. (You use tartaric, malic and lactic standards to identify where the spot will be) will become visible at its place on the paper. If I remember, a kit to do this is about $30 at the wine supply store. cheaper to have it done at a lab... or join with friends! The solvent is nasty stuff...so be very careful if you decide to try this!
Commercial wine labs buy thin layer chromatography paper which speeds things up to about 20 minutes developing time.
The ultimate is enzymatic analysis which requires a spectrophotometer ( mega bucks!!!) but is the most accurate.
With practice ml fermentation can be monitored by observing the drop in pH...which is slight but still occurs and you need a pH meter. If you listen to your wine you will hear soft "pops" as the ml fermentation produces CO2.
For the home winemaker, it is important to know ml fermentation exists and if you want to induce it...the results will be a drop in acid, increase in pH, softening of the taste and your prize wine won't become gassy and smell like sour milk in the bottle.
If you want more info., email me! Don't panic...go back and read the first paragraph in the winemaking notes!