THE SCIENCE OF CIDERMAKING Part 4 (2024)

Updated version now available in book form!

Part 4 - Customising your cider

In the last article we looked at the production of a straightforwarddry,still cider. In this part we shall look at the production of sparklingand sweetened versions, concluding with an outline of a traditionalFrenchand English technique which many regard as the pinnacle of thecidermaker'sart.

Dry carbonated cider

To get some bubbles into our cider we need to incorporate excess carbondioxide under pressure and to put the cider into bottles or into a kegwhich will withstand it. Then, when the pressure is released and thecideris dispensed, out come the bubbles! This is done commercially bychillingthe cider and dissolving two or three volumes of carbon dioxide in theliquid using special equipment. Small scale commercial carbonationunitscan be bought or, on a domestic scale, a bottle or two can becarbonatedusing a soda-syphon and a 'Sparklets' bulb.

It is more satisfying, however, to allow the fermentation itself togenerate the carbon dioxide by 'natural conditioning'. One way of doingthis is by racking and bottling the fermentation early, say at agravityof 1.003, and allowing the cider to finish fermenting and to mature inthe bottle. The CO₂ produced will dissolve in the cider toproducebubbles when the bottle is opened. A drawback to this technique is thatthe yeast deposit in the bottle may be rather heavy and coarselyflavoured.An alternative is to rack the cider into bottles after fermentation todryness, adding a small amount (10 g per litre) of priming sugar toeachbottle, and allowing a secondary yeast fermentation of the added sugarto produce the gas. This can be very successful although the bottom ofeach bottle will inevitably be a little cloudy when poured, becausetherewill always be some yeast deposit which will be roused up when thepressureis released. This problem can be lessened on a domestic scale bystoringthe conditioned cider in a pressurised keg or barrel similar to thoseusedfor home-made beer. In these devices the yeast drops to a below belowthedraw-off tap and a bulk, sparkling and clear cider is easily achieved.The ultimate way of avoiding the yeast problem is to produce a cider bythe 'methode champenoise', in which the yeast is removed by invertingandturning the bottle in stages until it is all collected in the neck.Thisis then frozen in an ice-salt mixture, the bottle is opened, the frozenyeast plug is forced out by gas pressure, and the bottle is topped upandresealed before the majority of the gas can escape. The quality of suchciders is legendary, although for obvious reasons they are labour-intensive to produce and therefore expensive to purchase!

Any bottles used for carbonated ciders must be designed to withstandthe pressure generated by the gas, or there is a serious risk of themburstingand causing injury (not to mention the mess!). Some years ago thereusedto be quart cider bottles with internal screw threads and specialthreadedstoppers, but these no longer exist. An alternative is to use glassbeerbottles which are sealed with a crown cork - these and the cappingtoolsare widely available from home-brewing suppliers. The industry has nowgone over almost entirely to PET (polyethyleneterephthalate) bottleswhichare lightweight and hold a moderate pressure well. Also, if they doburst,there is no risk of injury from flying glass. If you are making a smallamount of cider for home use, you can recover, rinse and re-use thesebottlesseveral times if they have previously contained other carbonateddrinks.If you cannot scrounge sufficient secondhand bottles or you are workingon a larger scale, you may have to buy new PET bottles from aspecialistsupplier. Non-carbonated ciders can of course be bottled in winebottleswith regular corks if required, but the bottles must be stored on theirsides to prevent the corks drying out and the air getting in (whichwillcause spoilage). Normal plastic (PET) bottles do allowoxygen inthrough their walls and so the flavour of the cider does alter overtime compared to natural conditioning in glass. However, there are PETbottles sold into thehome brew trade which do incorporate anoxygen barrier e.g. Coopers Oxbar brand, and it is well worth huntingthese out.

Sweet still cider

Even the 'dry' ciders described above may have a little residualsweetness,from the small amounts of non-fermentable sugars which exist in theoriginaljuice. However, many people prefer an overtly sweeter cider and so someway often has to be found of adding or retaining some sugar withoutrunningthe risk of it re-fermenting. This is difficult if any yeast remains inthe presence of an adequate supply of nutrients, because it willimmediatelyget to work on the added sugar. This will produce carbon dioxide gas,and if the bottle is sealed and the sugar level is too high then a"bottle bomb" will result, which could explode and take somebody's eyeout. Commercially, the problem is tackled bycentrifugation and filtration of dry cider to remove most of the yeast,followed by pasteurisation to eliminate the remainder after theadditionof sugar. This is not so easy to do on a small scale, althoughdisposable-sheetfilter units which can give near-sterile filtration (if properlyoperated)are available.The sweetenedcider is then treated through aflow-throughheat exchanger operating at 90^oC with a residence time of30seconds so that the pasteurised cider is filled directly into warmedbottles.Equipment of this sort does not come cheap and can usually only bejustifiedin the context of a commercial operation. Many large commercialcidermakers now use the techniques of sterile filtration and asepticbottling in place of pasteurisation but this is not within the scope ofthe amateur. The microbiological requirements are just toostringent, and even a few residual or stray yeasts may beenoughto cause an entire batch of sweetened cider to re-ferment.

Fortunatelyon a domestic scale youcan successfullysweeten your still cider to taste and thenpasteurise the filledbut unsealed bottles in a tank of hot water on a stove top, holdingthem until the cider reaches 66^oC. Use a digital thermometer in the bottles to be sure that the contentsreach the specified temperature.Then capthe bottles, take them out of the water bath and leave them to cool ontheir sides to sterilise the inside of the bottle neck and the cap.Crown or screw cap glass bottles can be used, but not plastic becauseit will not stand the heat. You can reduce the development of any'cooked' flavours by not overheating and by adding 30 - 50 ppm of SO₂before bottling. You can also pasteurise "bag in box" ciders in asimilar way - in the UK, such bags are avaialble in sizes from 3 to 20litres.

Ifyou don't want to pasteurise a sugar-sweetened cider, then your onlyreliableroute is to usea non-fermentable syntheticsweetener instead of sugar. Saccharin has been used to sweetenUK'farmhouse' ciders since the 1890's - for so long, in fact,that many unsuspecting people believe it to be a traditional andnatural ingredient. However, saccharin also has a nastyliquoricetaste and a long bitter aftertaste. The most successful artificialsweetener is the more recently introduced Sucralose,sold under the brand name "Splenda". The small compressed tablets areeach equivalent to one teaspoon of sugar in terms of sweetening powerand are ideal for just one glass of cider at a time, although they donot have the 'body' of sugar. Other sweeteners you might wish toconsider as an amateur are extracts of the herb Stevia (which is a high intensity natural sweetener) and Xylitol(which is a non-fermentable sugar alcohol with about the samesweetening power as sugar). Both are safe but neitherarepermitted for sweetening of commercial ciders in the EU at thepresent time.

Ifyou really want to sweeten dry ciders with added sugar (or with frozenorconcentrated apple juice) but you do not want to pasteurise or filterthem,itis important that they should be racked and stored for several monthsafterfermentation is complete, to allow the yeast to die outbeforethe sugar is added. But the shelf-life will be short and eventualre-fermentation isalmost inevitable, since some yeast cells will always survive and willmultiply.The chances of re-fermentation can be somewhat reduced by keeping thecider at refrigerator temperature (4 C) and by the addition of yeastinhibitors such as potassium sorbate and benzoate at levels up to 200ppm.(Both these materials occur naturally in rowan berries and cranberriesrespectively). Potassium sorbate may be bought from home winemakingsuppliers. It is most effective ifcombinedwith say 50 ppm of SO₂addedat the same time. In the absence of sulphite, sorbate is not soeffective and may alsolead to 'geranium-like'off-flavoursin the presence of malo-lactic bacteria. This sort of procedure issometimes recommended by people who keep and dispensetheir ciderfrom CO2-pressurised metal kegs which are stored in the refrigerator.ButI do notadvise the 'preservative' route for longkeeping of sweetened cider, and certainly not when using glass bottles- the risk of instability and explosion isjust too great. If you are using apple juice concentrate forsweetening, be aware that this is not sterile and containsosmo-tolerant and preservative-resistant yeasts such as Zygosaccharomyces bailii which will grow quite happily in the presence of sorbate and SO₂.

Traditionally, naturally sweet ciders were made from slowfermentationswhich are poor in nutrients. Ciders which show an S.G. loss of lessthanone degree per day may besuitable for this treatment. The cider is rackedinitially into a new clean tank at say S.G. 1.030, leaving most of theyeast behind. The fermentation will then become even slower, and thesweetcider is racked again (and preferably filtered) at S.G. 1.020 - 1.025.(Racking at S.G. 1.015 will give a medium sweet cider). After thisrackingit is worth waiting several weeks (under an air lock) to ensure that nofurther fermentation takes place, before sealing the vat tightly orbottlingoff.

Sweet carbonated cider

This, which mimics most commericalcider, is the most difficult sort of cider to make at home. Theequipment and discipline needed to achieve force carbonation(togain bubbles) and pasteurisation or sterile filtration (toprevent refermentation) in the same bottle is simply not available tothe amateur. There are a number of posssible workarounds, though:

1.If you have a very slow natural fementation as described above, you mayget a certain degree of light carbonation in bottle. Taking this onestage further, you can employ the old technique of"keeving" as described below.

2.If you use an unfermentable sweetener like saccharin, sucralose, steviaor xylitol, you can combinethis with the technique for 'natural conditioning'described above, to produce a non sugar-sweetened but carbonated cider.(The sugar you add for carbonation will not contribute to thesweetnessbecause it will be fermented out).

3. You canbottle ferment with added sugar, and then pasteurise the sealed bottlesafter daily testing when you have got to the required sweetness level.This is described in the Ag Canada booklet here. But beware because exploding bottles are a very real possibility. Goggles should beworn!

Blending

Blending of ciders, if required, should always be carried out wellbeforethe final racking for storage or bottling. This is because the changesin acidity, nutrients and yeast levels, which occur when differentbatchesare mixed, may affect the stability of the bulked cider and allow it toferment further, even if the individual ciders were stable beforeblending.Similarly, if clear ciders are blended together they are quite likelytothrow down a new haze or deposit which may need time to settle down.Thegeneral principle of blending is to ensure a flavour balance which isunobtrusive,particularly in terms of its acidity and tannin. It is best to takesmalltest quantities of the ciders to be blended, and sweeten these first tothe S.G. which will be required for the final blend (1.025 for sweet,1.015for medium sweet). Then a measuring cylinder should be used to blendequalparts of those ciders which are highest and lowest in tannin. Theproportionsshould be varied until acceptable tannin levels are achieved, and theoperationrepeated for any other ciders which are unbalanced in tannincomposition.If the tannin levels are too low because no bittersweet fruit was used,it is possible to increase them by the addition of grape or other foodgrade tannin (in 0.1% steps) until a satisfactory level is achieved.Carefulnote should of course be taken of the volumes used for blending and theamount of any tannin added. If the tannin levels are too high becauseofa large proportion of bittersweets, then fining with gelatin can beconsidered.This is covered in the next article.

The trial blends which are now balanced for tannin can be blendedforacidity following a similar routine. If the addition of acid isrequired,malic acid may be used in 0.1% steps. Removal of acid is difficult atthisstage, but may be done if necessary by the addition of potassiumcarbonate- calcium carbonate used here tends to leave a residual chalky flavourin the cider. The trial blends now have the correct tannin and acidbalance,and they can finally be corrected for other more subtle flavours andaromasby blending amongst each other. Finally, the main bulk of ciders can beblended according to the proportions determined by the trials butwithoutthe addition of the sugar at this stage. For reasons explained above,theciders must be allowed to stabilise further in bulk store beforecorrectingthe sweetness (unless filtration and pasteurisation are used to preventall possibility of re-fermentation).

French and English tradition ("keeving")

We have now seen how to ferment, blend and bottle a number of styles ofcider. It is now worth looking at the production of high qualitynaturallysweet ciders by the best traditional French and English methods. Theobjectiveof these is to lower the nutrient status in various ways so that thefermentationremains slow and the natural sugar can be retained without fear ofre-fermentation.

A blend of fully ripened sharp and bittersweet fruit is used fortheseciders, taken from mature orchards which are naturally low in nutrientsbut fairly high in tannin. Dessert fruit is much less likely to besuccessfulhere, due to its generally low tannin and high nutrient levels. Thesugarlevel should be at least 12% (SG 1.055). The fruit is stored until acoldday late in the year when the temperature is about 5^o C andexpected to remain so for a week or more. The fruit is washed andmilledin the normal way, but the pulp is then packed into barrels (or,better,plastic containers) to stand for up to 24 hours. This is the procedureof 'maceration' or 'cuvage', terms with no particular Englishequivalent.During this time, oxidation slowly proceeds which develops the juicecolour,and pectin leaches out of the apple cells into the juice. The juice isthen pressed out, rich in colour and thick in texture, and is run intoclean tanks which are allowed to stand without sulphiting or theadditionof yeast (author's note: If the pH is around 4, which it is likely tobe,I do actually add 100 ppm sulphite at this stage to provide someinhibitionof bacterial infection. The 'official' French recommendation is to burn10 grams of sulphurated string in the barrel!!)

Since the temperature is low, no significant yeast fermentationtakesplace, but the natural pectic enzymes in apple juice slowly change thepectin to pectic acid. This forms a gel with the natural calcium in thejuice and a 'brown head' (the 'chapeau brun') rises slowly to thesurface.Some of the pectin also combines with juice protein and tannin andfallsas a sediment to the bottom, leaving a clear juice between the two. Tomake this process more reliable, a mixture of calcium carbonate (3 gper10 litres) and sodium chloride (4 g per 10 litres) is often added tothefresh-pressed juice - the calcium helps to form the gel, while thechloridehelps to inhibit the growth of any yeast (author's note: I add 400 ppm(4 g per 10 litres) of calcium chloride which is a one-shot way ofachievingthe same thing). A specially prepared pectin methyl esterase enzyme(whichis not the same as a regular pectinase) can also be added as described here. This process isknown inFrench as 'debourbage' or 'defecation' (for obvious reasons!) and inEnglishas 'keeving', and generally takes about a week. If things go wrong, anda yeast fermentation starts too early, a 'white head' (the 'chapeaublanc')is formed. This means that the whole vat has become turbulent and thekeevinghas failed!

If the keeving has been successful, however, the clear juice betweenthe top cap and the bottom sediment is very carefully pumped orsyphonedinto a fermentation vat. It is now allowed to ferment under an air-lockin the normal way (with its own yeast), but this fermentation will beveryslow because most of the nutrients in the juice will have been leftbehindin the 'brown head' and in the sediment. In fact, scientific study hasshown that the pectin and the amino nitrogen nutrients are reduced byatleast 50% during keeving. With such a slow fermentation it should be noproblem to make a naturally sweet cider, by racking at S.G. 1.030 andproceedingas described earlier. Preferably the ciders should be bottled incrown-capbeer bottles which are stored in a cool place for maturation -they CANget quite fizzy if allowed to warm up too much during the summer!

The advantage of this process is that it can produce a naturallysweetand well-coloured cider, brilliantly clear due to the removal of pectinduring keeving, and full of flavour because of the low nutrient levelsduring fermentation. The disadvantage is that a lot of it depends onluck- the correct fruit, cold weather, benevolent strains of wild yeast andfreedom from bacterial infections! What actually happens is that thefermentationbegins with so-called apiculate' yeasts from inside the applespredominanting- these then slowly die out as the alcohol level rises and the Saccharomyces( wine yeasts') slowly take over to complete the job. If you get thechanceto look at the yeasts under the microscope, as I have done, you'll seeall shapes and sizes of organisms imagineable. This is quite differentfrom a fermentation with an added yeast, where all the cells areidentical.

(Author's note: In my experience, the flavour immediately after evena well-conducted 'natural' fermentation is heavily dominated by ethylacetate,and can be really quite unbalanced and unpleasant to drink. A fewmonthsstorage in bottle, however, can work wonders in blending out theseflavoursto something really magnificent. Not everybody likes it, though - afriendof mine described my best quality cider as 'tasting like smoky bacon'(whichis due to the natural tannins breaking down to give 'spicy'flavours)!!)

There is plenty of scope here for anyone who wishes to experimentwithdifferent parts of the process. For instance, the final colour andclarityof the cider is critically dependent on the length of 'cuvage', duringwhich the oxidising enzymes produce colour from the tannin, and thepectinslowly migrates out of the fruit into the juice. If the pulp is heldtoolong a time, the rich orange colour of the final juice will actuallydiminishand the flavour will become insipid due to excessive adsorption ofoxidisedtannin back onto the pulp. If the pulp is held too short a time, notenoughpectin will migrate out into the juice to form a good 'head' duringsubsequentkeeving and so, paradoxically, effective clarification and nutrientremovalwill not be achieved. If the pulp is tightly packed and too little airis present during 'cuvage', too little colour will be developed - butifthe pulp is loosely packed and too much air is present, spoilageorganisms(vinegar bacteria) will quickly take hold. If the weather is too cold,none of the desirable enzyme activity will take place - but ifconditionsare too warm, yeast fermentation will begin too early and the keevingwillfail. If the pH of the fruit is too low (less than 3.6) the naturalpectinaseactivity may be too slow to form a successful 'brown head' - but if thepH is too high (greater than 4) undesirable film yeasts will develop tothe detriment of the required Saccharomyces species.

Balancing these factors (and many more) relies on judgement andexperienceand was part of the skill of the traditional cider maker, although heknewnothing of the biochemistry behind it. The new traditionalist should beable to build on this skill the better, if he only bears in mind thescientificprinciples of what he is trying to do!

So far we have considered cidermaking when everything goes accordingto plan. In the next part of the series we shall look at some of themorecommon things that may go wrong, and what we can do about them.

Menu and Home Page

Back to Part 3

Forward to Part 5