Here are the basics of Keeving and the French production methods we have gleaned so far in our trip to France and England.
By David Takush, 2 Towns Ciderhouse
We have found that only approximately half of the producers actually try to achieve a 'chapeau brun' -the 'brown hat' that forms at the top of a juice tank and results in an over-clarified must essential for a keeved cider. We found both large and small producers using the chapeau brun method as well as the alternative method of 'sedimentation'. Only larger producers are pasteurizing their final product in bottle, however many of the smaller producers have issues with over carbonated cider, undercarbonated cider, or cider that is slightly off of the ending target gravity.
In general, we have seen chapeau brun achieved by harvesting mature fruit from the orchard floor. Most growers are letting fruit naturally fall off the tree, and making up to three harvests under each tree. Sometimes the tree receives a shake if needed. This fruit is usually processed the same day or the following day of harvest. Some producers have a slightly extended storage time for apples, but usually just a few days. The number one aspect of achieving chapeau brun was said to be the maturity of the apples, but we have no quantitative measure for this level of maturity, only visual inspection of seeds and taste, and the fact that most of the fruit has fallen or is falling out of the tree. After washing, sorting, and grinding the apples, the pomace is left to sit for 1-4 hours (usually while the previous press is finishing). This time of maceration seems dependent on temperature and process flow through the cidery. Larger operations trying to achieve chapeau brun will actively mix the pomace for oxidation purposes before pressing. Some English producers will leave the pomace to sit overnight.
We have seen three types of presses in use: belt presses, wine bladder presses, and bucher-type pneumatic presses. The wine and bucher type presses take 1.5-2.5hours to press a batch. It has been suggested that belt presses press too quickly and do not allow enough oxidation to occur, however we saw people achieving chapeau brun with belt presses, usually in conjunction with extended maceration (though sometimes not).
The juice after pressing is usually cooled (if cooling equipment is available) in a mixing tank or a tube and tube heat exchanger down to 8-12c before pumping into a tank. Sometimes juice is sulfited in minor quantities of 5mg/HL. PME (pectin methyl esterase) is added upon the filling of the keeving tank at a rate of 1L per 300hL (depending on concentration of enzyme and manufacturers suggestion). Usually the next day CaCl is added to the tank at a rate of 15L per 300L (again, dependent on manufacturer's recommendation) then sometimes mixed by pumping 20min-1hour.
After 1-3 days a chapeau brun (coagulated and aggregated pectin) begins to form in the juice and 5 days and up to 2 weeks later (depending on temperature, which is usually 8-12c) the chapeau brun has fully formed at the top of the tank and clear juice is ready to be racked out the middle of the tank.
Another form of clarification known as sedimentation can be used to achieve a clear and nutrient deficient juice. Pectinase (polygalacturonase) can be added in-lieu of the PME and CaCl, which will drop all sediment and degrade pectin causing the particulates to drop to the bottom of the tank. The clear juice is then racked off the top.
Once a clear juice has been achieved and racked to a fermentation tank, sulfites may be added in very small quantities of 5mg/hL, if desired. After a number of days depending on temperature, fermentation will begin. Optimum temperature is 8-12c. The optimum rate of fermentation is 1-3 gravity points (specific gravity, aka density) per week. The slower rate the better and 4 points/week and over is too much. This rate of fermentation is managed (slowed) by temperature and racking from tank to tank, centrifugation, or by filtering 90% of the liquid (DE or cross flow).
The regrowth of new yeast generations after each subsequent racking or clarification uses up yeast available nitrogen, the lack of which will play a part in allowing residual sugars to remain in the unpasteurized finished product.
One remaining question is how to know when to do the racking or filtration steps during fermentation. Some producers have specific density readings: such as 5 or 10 points of gravity loss, some observe the fermentation getting too cloudy or going too fast.
After fermenting and reaching the ending density required for Demi-sec, brut, etc., a final crossflow or DE filtration or plate-and-frame step may be applied along with an optional 3-5mg/hL of sulfites. This usually occurs between 2-4 points above their final target gravity, allowing for a drop during re-fermentation in the bottle to hopefully arrive at 2.5-3.5vol co2. Some producers do more extensive bottle conditioning testing or final YAN counts, most do not. Some producers, especially those who do a final crossflow step, may need to add an extremely small amount of commercial yeast to their cider for proper bottle conditioning to occur. Most bottle conditioning is around 3+ months in bottle at 8-12c.
YAN levels at juicing are usually 40-60. 80ppm appears to be too high. Yan levels at bottling appear to be 20-40 depending on ending gravity (less for brut, more for demi-sec).
Most producers prefer pH not to go over 3.84pH and will sometimes add malic acid to lower their numbers. 3.7pH seems to be optimum. Some producers track Malo-lactic fermentation, most assume it will complete all the way, but hope it will happen later in the fermentation process or in the bottle.
We have been told a variety of ranges of pH you can keeve at. Some said down to 3.4-3.5. Most said the lowest pH for keeving was 3.6. Most producers in France and England do not seem to track total acidity, nor care. It has not been answered whether T.A. also plays a role in the formation of chapeau brun, but it is assumed that too high of total acidity and/or too low of pH can inhibit chapeau brun formation. One note is that multiple English producers appear to be getting chapeau brun formation with a significantly higher proportion bittersharp apples than what the French commonly use, which is no more than 10% sharp apples and a majority sub-acid apples. Additionally it has not been answered if tannins are a required part of the formation of chapeau brun, since nobody ferments without tannic cider fruit in France or England.