A couple of weeks ago, I discussed about the additives employed in molecular gastronomy, mentioning pectins. You might have heard about them or found them listed among the ingredients of some food.
Pectins are complex carbohydrates, namely long-chain sugars. Together with celluloses, pectins form the wall of vegetable cells. People who commonly prepare home-made jams might use pectins to help the jam to set. One of the main properties of pectines is, indeed, to be a gelling agent (I told you that discussion on gels was far from being completed :)).
Pectins, jams and fruit pastes
One of the most common use of petins is, doubtlessly, preparation of jams, jello and fruit pastes (all gels). When making cooked-jams, we simply extract the pectins that are naturally contained in the fruits. Certain fruits as apples, pear, quince, are richer in pectins than others. You might have heard about the old-fashioned tip of adding some apple peel when preparing a jam. The apple peel adds more pectins to the mixture and help the jam to set.
Traditional preparations of jams requires a long time, as the mixture must simmer for a few hours. That is the phase when pectins get extracted from fruit. Furthermore, the sugar added to the mixture make a syrup that, because of osmosis, attracts the water from the fruit. The jam is then let cool down and the pectin chains take contact and associate with each other, forming a net that traps water. The gel, better known with the name of jam, is so formed.
Commercially available pectins are usually extracted from fruit peel, in particular, from citrus. They have a crystalline appearance, quite similar to sucrose, the common table sugar. Adding pectins speeds up the preparation of jam, as there is no need to extract them from fruit by simmering for hours. You just add them to the fruit mixture and, voilà, your jam is ready in a couple a minutes. Some people look at this method in a suspicious way, probably because it diverts from tradition. However, addition of pectins has advantages:
- short preparation time: you do not have to simmer for hours
- appearance: the jam looks fresher and the taste is more authentic, as fruit is not boiled for hours
What affects the gelling properties of pectins?
Pectin gels are more sensitive than those made of collagen (gelatin). Concentration of certain ions, pH and sugar percentage are all factors that must be taken into consideration when dealing with pectins. I hate to be a stickler, but underestimating even one of this parameter can leave you with a lot of disappointment. Let’s discuss them more in detail.
You might have heard the old tip of making jams in a cupper pot. It is not an urban legend: there is, actually, an explanation behind the story. Pectins contain carboxylic groups that are negatively charged above certain values of pH. Bivalent positively charged ions, namely ions carrying two positive charges (e.g. Cu2+, Ca2+), electrostatically interact with the pectin chains and bring them closer. However, given the toxicity of copper, I would avoid using it to make jams :P (our body just requires trace amount of copper). I believe no one uses copper pots to prepare jams, anymore.
A similar effect is, however, induced by calcium ions (Ca2+). I read about a popular French pastry chef who replaced tap water with a purer one to prepare an apricot confiture. As a result, the confiture didn’t jell. Waters with higher concentration of calcium are, therefore, more indicated in the preparation of jams.
pH is measure of acidity. Below, I reported the pH scale that, as a convention, goes from 0 to 14. The value of 7 refers to neutrality. Below 7, we have acidic substances, while above 7 basic ones.
pH significantly affects pectin gels and has a crucial role in the preparation of fruit pastes. Do not underestimate it: I did it once and I have learnt my lesson. But this is anther story, for another time ;)
Pectines form gels in acidic environments, usually in a pH between 3 and 4. If the pH is acidic enough, carboxylic groups get protonated and do not repulse each other. This promotes the association of pectin chains, which form the gel net.
R-COO- + H+ → R-COOH
This explains why acidifying agents, as tartaric, ascorbic or citric acid, are used to make fruit pastes. They maintain both pH around 3-4 and carboxylic groups protonated, helping thus the formation of the gel.
Concentration of sugars
Simple sugars as sucrose, the common table sugar, determine the good outcome of jams and fruit pastes.
Sugars dissolve and form a syrup that attract water from cells, because of osmosis mechanism. Moreover, they play a role in jam setting and are good preserving agents. It was calculated that sugar content in jams should be around 50-65% for a good outcome.
Type of pectin
There are several types of pectins, but in pastry two are commonly used: LM (low methoxylation) and HM (high methoxylation). What do they mean?
Carboxylic groups can react with alcohols as, for instance, methanol. This reaction is called esterification. After this reaction, the carboxylic groups (that are now esters) are not charged anymore and do not repulse each other.
LM pectins have a low degree of esterification, while the HM types bring a higher percentage of esters. LM pectines jell in the presence of calcium ions. If you purchase this kind of pectins, you should find a pouch of calcium salt to be added to the preparation. On the other hand, HM pectins require only an acidic environment to jell and are often added of acidifying agents.
As you might have understood, pectins are not easy to handle. Pectin gels are affected by several parameters, sometimes interdependent. For such a reason, I strongly recommend to stick to the recipes you find. If you start to replace this with that and/or changing doses, you might end up with a disappointing results. Unfortunately, not all recipes with pectins are so accurate. Sometimes, the type of pectin (LM or HM) is not indicated. You can, however, guess the kind of pectin by the presence of calcium ions: if they are not listed, the pectin is probably a HM type.
Have you ever tried to use pectins for your jams? How did it go?
Hervé This, Les précisions culinaires, pag. 30, 40, 179-180, Edizioni Quae Belin
Hervé This, Pentole e provette, pag. 48-49, Edizioni Gambero Rosso
Leonardo Di Carlo, Tradizione in evoluzione, pag. 592-593, Chiriotti Editori
M. Migliori, Reactive and Functional Polymers, 2010, 863-867