The Brixacid Ratio

As mentioned previously, the juice of a ripe fruit has a dissolved solids content (Brix) characteristic of that particular fruit species. This is also the case for the acid content of a fruit juice. The levels of both of these items in the juice may vary in a narrow range depending on climatic and environmental conditions in which the fruit was grown as well as on the ripeness state of the fruit when harvested.

As these two values of Brix and acidity are more or less distinctive for each fruit species, the consequence will follow that the ratio of the two values will also have a distinctive value typical for the fruit species. This ratio is termed the Brix/acid ratio (sometimes also referred to as the dissolved solids/acid ratio). This ratio of Brix to acidity could be described as the "sweetness to sourness" relationship in the taste of the juice.

In lemon juice, the Brix (corrected for acidity) of single-strength juice is, on average, 7.5°B, and the acidity is at around 5.0% (as citric acid anhydrous w/w). Therefore, the Brix/acid ratio of lemon juice will work out to 1.50. In another fruit juice, orange for example, the Brix/acid ratio can be in the range of 8.0 to 12.0.

What do these two figures tell us? They indicate that the orange is much sweeter to the taste than the lemon. Well, we do not really need the Brix/acid ratio to tell us such a well-known fact. What then is the purpose and importance of the Brix/acid ratio concept?

The fruit juice processing industry together with international government agricultural and food organizations established the standards of Brix/acid ratio specifications for most of the world's known edible fruits. The values established are expressed as a Brix/acid ratio range or a minimum

The ratio of juice Brix to acidity is characteristic of a particular fruit species.

(or maximum) limit. If a fruit juice is tested for its Brix/acid ratio value, and the result obtained does not meet the specification of that particular fruit species juice, then something is wrong. Either the juice is not of the fruit it purports to have been derived from, or the juice has somehow, deliberately or unwittingly, been modified from its natural composition.

In this sense, the Brix/acid ratio specification serves as a A deviation from the Brix/acid ratio simple "fingerprint-type" parameter for the identification of a specification indicates that some- fruit juice and for products derived from these juices. If we take thing is amiss with the juice. our lemon juice as an example and find that its Brix/acid ratio is 3.5, well above the stipulated 1.5 value, one reasonable conclusion is that it was sweetened with extra added sugar. This added sugar will increase the value of the Brix/acid ratio value. This is no great train smash — it is permitted to sweeten a lemon juice product, but it can no longer be called pure lemon juice. It would most probably be described on the label as "sweetened lemon juice." If not, then the most likely conclusion would be that the lemon juice was adulterated.

Adulteration of fruit juices is of major concern to the public and industry authorities all over the world. The Brix/acid ratio is the first step in identifying this unscrupulous practice. Other steps are much more sophisticated but will not be discussed in this handbook.

The link of the Brix/acid ratio concept to soft drink technology, the real subject of this chapter, is somewhat less dramatic and can be briefly described as follows. In the soft drinks industry, other than in the companies that have a core business in the fruit juices and nectars category, the intricacies and quirks of juice technology are not commonly known to technical and other involved staff who may be dealing with juice ingredients present in some of their company's ranges of products. They cannot be blamed or faulted in this respect, as they are most probably very much involved with their own core nonjuice business technology issues. This is particularly true of the smaller independent and private companies that do not usually have the luxury of head office boffins and specialists to help them out.

Here is where the Brix/acid ratio can be of some assistance. An "out of spec" Brix/acid ratio Every batch of incoming fruit juice should have the supplier's should be immediately queried with blessing in the form of a certificate of analysis (COA) specifying the supplier. the Brix/acid ratio value of the batch. If in-house routine testing of Brix and acidity by the QC staff of the company results in a calculated Brix/acid ratio out of the stipulated specification, then something is amiss with the batch. It is not necessarily a case of deliberate adulteration but rather, most probably, a processing error on the part of the supplier or processor. For instance, it may be a case of the processor having used fruit that was harvested too early and had not ripened fully, in which case the Brix/acid ratio would be much lower than usual. Alternatively, if the juice is of the sweetened type, too much sugar may have been added in error. Then the Brix/acid ratio would be too high.

It could be argued, and justifiably so, that if the Brix and acidity quality parameters of a juice are found to be within specification, the corollary of a Brix/acid ratio within specification should follow. So why use the Brix/acid ratio parameter? The answer is that this is not altogether quite true. The Brix as an individual specification may be at its highest permitted value and the acidity, also as a specification on its own, at its lowest tolerance value. The ratio then may exceed the prescribed Brix/acid ratio for which the processor must be held responsible. The same applies to the reverse — lowest Brix and highest acidity could result in a ratio lower than specified.

A second argument in this respect is that an individual Brix (or acidity) value of the juice may be slightly higher than the allowed specification, and the consignment could still be released for use in production, as no great calamity could be caused by an extra bit of dissolved sugar in the juice (after all, it would be a case of "money for nothing"). But, the Brix/acid ratio calculated could well be out of specification. This implies that something is wrong and needs to be addressed with the supplier. The Brix/acid ratio, therefore, serves as a cherry on top of the cake of your confidence in that the processor used good, wholesome, ripe, and fresh fruit for processing your juice, and he has processed it correctly. After all, as with all ingredients used in your facility, you are interested in juice of the highest quality available.

Strictly speaking, a deviation in one of the parameters, as in both arguments above, should always be accompanied by an equivalent change in the other, and in the same direction. This is the boon of a ratio-type specification between two individual parameters — they should always go hand in hand together. If not, "something is wrong." To sum it up in another way, if you draw your juice supplier's attention to Brix/acid ratio issues you may come across, he will only develop more respect for your technical acumen, and that is not a bad thing at all.

Last but not least on the subject of the Brix/acid ratio of juices: If you are involved in new product development and want to formulate products with little-known exotic-sounding fruit species, the knowledge of their Brix/acid ratio values could well serve as an indication of their potential sweetness and sourness effects on the new products. This, in turn, could guide your overall taste profile design of new products in respect of what target sugar and acid levels these should have. If, for instance, the exotic obscure fruit of a new planned beverage has the same Brix/acid ratio of orange, build your new product formulation on a composition template similar to an existing orange formulation in your company's range of products. This will save you a lot of time in trial and error steps to achieve a reasonable prototype formulation on which to work.

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